Bees and wasps: some myths and how to tell them apart

Despite being part of the same order of insects (Hymenoptera), bees and wasps have well differentiated traits and habits; however, it is very common for people to confuse them. In this post, we will give some simple clues to differentiate between them, and deny some of the most common myths that revolve around these organisms.

Bees and wasps: how to tell them apart

Before differentiating them visually, we should start by classifying them.

Both bees and wasps are part of the Hymenoptera order, which are characterized by two pairs of membranous wings that remain coupled during the flight thanks to a series of tiny hooks (hamuli); in addition, they usually present antennae more or less long, of 9-10 segments at minimum, and an ovopositor that, in certain groups, has evolved to become a sting. Within this order, both bees and wasps are classified within the Apocrita suborder, which are characterized by having a “waist” that separates the thorax from the abdomen.

As for Apocrita, this suborder is traditionally divided in two groups: “Parasitica” and “Aculeata”, which we’ve already mentioned in the post “What are parasitoid insects and what are they useful for?“:

• “Parasitica”: very abundant superfamilies of wasps that parasite arthropods (chalcidoidea, ichneumonoidea, cynipoidea, etc.), except for the family Cynipidae (gall wasps), which parasite plants. None of these wasps have a sting, so no worries!
• “Aculeata”: includes most of the so-called wasps and bees (as well as ants), most of which have stings.

So far, we can see that there are a large number of parasitic wasps that differ clearly from the rest of bees and wasps with sting. If we continue to deepen, within the “Aculeata” we typically distinguish three superfamilies:

• Chrysidoidea: group formed by parasite wasps (many of them kleptoparasites) and parasitoids. The Chrysididae family (cuckoo wasps) is very popular due to its metallic coloration.
• Apoidea: includes bees and bumblebees, as well as the formerly known as “sphecoid wasps”, most of which have become part of another family of Apoidea (Crabronidae)
• Vespoidea: mostly formed by the typical stinged wasps (eg Vespidae family) and ants.

Cuckoo wasp (Chrysididae). Author: Judy Gallagher on Flickr, CC.

Simple keys to differentiate

After this review, many will think that this separation of wasps and bees is not so simple; and those of you who do will be right. While bees and bumblebees belong to a monophyletic lineage (this is, a group that includes the most recent common ancestor and all their descendants) and their characters are quite clear, the concept of wasp is somewhat vaguer.

Here are some basic morphological and behavioral traits to differentiate the most common wasps and bees. These traits are easy to spot in a simple way, and in the eyes of expert entomologists, they may be very general (there are many other complex characters that make it possible to differentiate them); however, they can be useful when you do not have much experience:

• Bees (and specially bumblebees) tend to be more robust and hairy than wasps. Wasps do not show “hair” and tend to be slender, with thorax and abdomen more widely separated.

Left: western honey bee (Apis mellifera); author: Kate Russell on Flickr, CC. Right: wasp from the genus Polistes; author: Daniel Schiersner on Flickr, CC.

• Most of bees present corporal adaptations for the collection of pollen, which they receive the name of scopa. In most, these are limited to the presence of many hairs on the hind legs. However, there are special cases: in the western honey bee (Apis mellifera), in addition to having pilosities, the tibias of the hind legs are very widened, forming a kind of blades with which they collect the pollen; on the other hand, the solitary bees of the Megachilidae family do not have pilosities on the hind legs, but a series of hairs on the ventral side of the abdomen.

Left: western honey bee (Apis mellifera) with the hind legs full of pollen; author: Bob Peterson on Flickr, CC. Right: Megachile versicolor, with the scopa in the ventral side of the abdomen; author: janet graham on Flickr, CC.

• Most wasps have chewing mouthparts (jaws retain their function), while in most bees mouthparts are lapping type, as we explained in the post “Evolutionary adaptations of feeding in insects”.
• Some wasps, especially certain parasites and parasitoids, present a much simpler wing venation, represented by a few marginal veins. This is the case, for example, of the families Chalcidoidea and Cynipidae.

Halticoptera flavicornis male, Chalcidoidea (a parasitoid wasp); author: Martin Cooper on Flickr, CC.

• If you see a slender hymenopteran with a very long “sting”, do not be afraid: it is probably the female of a parasitoid (eg a member of the family Ichneumonidae), and that long “sting” its ovipositor.

Ichneumonidae female of the species Rhyssa persuasoria; author: Hectonichus, CC.

• Many wasps fly with legs more or less extended because, with rare exceptions, they are hunters.
• As we approach a plant with flowers, we will observe a large number of insects flying and perching on them. Almost certainly, most hymenopterans we will observe will be bees, since all adults and almost all larvae are phytophagous (they feed on plant products), namely nectar and pollen.

Western honey bee. Public domain (Zero-CC0).

• If you’ve ever left food in the open, you must have seen a hymenopteran come to it. The larvae of most wasps are carnivorous, so adults take the least opportunity to catch prey for their offspring … or bits of something that you are eating.

Author: rupp.de, CC.

This is not over yet: myth busting

Now that we know how to differentiate them roughly, let’s confirm or deny some of the most common myths around bees and wasps:

• “Wasps do not pollinate plants“

False. It is true that bees play a very important role in pollination: their feeding based on the intake of nectar and pollen makes them visit many flowers and, in addition, they present many pilosities in which it is adhered. However, most adult wasps also ingest nectar, in addition to other foods. Although they do not present as many pilosities as bees, the mere fact of visiting flowers causes that their body comes in contact with pollen and part of it is adhered.

There is also the opposite case: some bees such as Hylaeus and Nomada (the latter known as cuckoo bees, kleptoparasite bees whose larvae feed on pollen stored in nests of other solitary bees) do not have adaptations for pollen transport, and their appearance is closer to that of a wasp.

Left: Hylaeus signatus male; author: Sarefo, CC. Right: solitary bee of the genus Nomada; author: Judy Gallagher, CC.

• “All bees are herbivorous, and all wasps carnivorous“

False. Although almost all bee larvae feed on pollen and nectar, while wasp larvae do on prey that adults hunt or parasite, there are exceptions. The larvae of gall wasps (Cynipidae family) feed on the plant tissue of the gall itself where they develop, whereas the larvae of a small group of bees of the Meliponini tribe (genus Trigona), present in the Neotropics and in The Indo-Australian region, feed on carrion, the only bees are known non-herbivorous.

• “Bees form colonies, and wasps are solitary“

False. There are both colonial and solitary wasps and bees. Honey bees are the most typical colonial bee, but there is an enormous diversity of solitary bees that build small nests in pre-established cavities or ones they dig. In the same way, there are also colonial wasps, like some of the genus Polistes (paper wasps) that build hives in which certain hierarchical roles are established (although they are usually smaller than those of bees).

• “All bees and wasps can sting“

False. The bees of the Meliponini tribe, also called stingless bees, have a sting so small that it lacks a defensive function, so they present other methods to defend themselves (biting with their jaws). In addition, females of some bees (eg Andrenidae family) do not present sting. Of course, all male bees and wasps have no sting, as that it is the modified ovipositor.

• “Bees die when they sting; wasps can sting several times”

Partly true. In honey bees of the species Apis mellifera, the surface of the sting is covered with a series of beards that give it the look of a saw, so that when removed, the sting is nailed to the surface of its victim, dragging behind it all the abdominal content to which the sting is adhered. In wasps, solitary bees and bumblebees, on the other hand, the surface of the sting is almost smooth or the beards are very small, being able to retract them and thus remove the sting without problems.

Sting of Apis mellifera; author: Landcare Research, CC.

• “Wasps are more aggressive than bees“

It depends. Wasps commonly nest anywhere, so people and other animals are more likely to come into contact with them. By contrast, bees often have preferences for certain places, usually more protected, not being so exposed. However, this is not always how it happens: the african bees, to which we dedicated a post, can nest almost anywhere and they are very aggressive!

• “Wasps are more colorful than bees“

False. In fact, partially false. Having no apparent hair, the color of wasps is usually more striking in general terms. However, there are genera of bees, such as the solitary Anthidium (which present a very striking abdominal coloration) or the orchid bees, which look similiar to wasps. In the same way, there are wasps of dark coloration and less jazzy.

Anthidium florentium male; author: Alvesgaspar, CC.

.        .         .

Despite there are much more differences between bees and wasps, we hope these tips can help you to tell them apart…and to love them the same way!

REFERENCES

• Michener, C. D. (2000). The bees of the world (Vol. 1). JHU press.
• Landcare Research (landcareresearch.co.nz): Stings.
• United States Department of Agriculture (USDA): Wasp pollination.

Main images property of Kate Russell, CC (Left) and Daniel Schiersner, CC (Right).

 

Plants and animals can also live in marriage

When we think about the life of plants it is difficult to imagine without interaction with the animals, as they establish different symbiotic relationships day after day. These symbiotic relationships include all the herbivores, or in the contradictory way, all the carnivorous plants. But there are many other super important interactions between plants and animals, such as the relationships that allow them to help each other and to live together. So, this time I want to present mutualism between plants and animals.

And, what is mutualism? it is the relationship established between two organisms in which both benefit from living together, i.e., the two get a reward when they live with the other. This relationship increase their biological effectiveness (fitness), so there is a tendency to live always together.

According to this definition, both pollination and seed dispersal by animals are cases of mutualism. Let’s see.

POLLINATION BY ANIMALS

Many plants are visited by animals seeking to feed on nectar, pollen or other sugars they produce in their flowers and, during this process, the animals carry pollen from one flower to others, allowing it reaches the stigma in a very effective way. Thus, the plant gets the benefit of fertilization with a lower cost of pollen production, which would be higher if it was dispersed through the air. And the animals, in exchange, obtain food. Therefore, a true relationship of mutualism is stablished between the two organisms.

 “Video:The Beauty of Pollination” – Super Soul Sunday – Oprah Winfrey Network (www.youtube.com)

The extreme mutualism occurs when the species evolve depending on the other organism, i.e., when there is coevolution. We define the coevolution such as these evolutionary adaptations that allow two or more organisms to establish a deep relationship of symbiosis, due that the evolutionary adaptations of one specie influence the evolutionary adaptations of another organism. For example, this occurs between various orchids and their pollinators, as is the well- known case of Darwin’s orchid. But there are many other plants that also have co-evolved with their pollinators, as a fig tree or cassava.

In no way, this should be confused with the trickery produced by some plants to their pollinators, that is, when they do not obtain any direct benefit. For example, some orchids can attract their pollinators through odours (pheromones) and their curious forms that resemble female pollinator, stimulating them to visit their flowers. The pollinators will be impregnated with pollen, which will be transported to other flowers due to the same trickery.

Bee orchid (Ophrys apifera) (Autnor: Bernard DUPONT, flickr).

SEED DISPERSAL BY ANIMALS

The origin of seed dispersal by animals probably had occurred thanks to a co-evolutionary process between animals and mechanisms of seed dispersal in which both plants and animals obtain a profit. The most probably is that this process began in the Carboniferous (~ 300MA), as it is believed that some plants like cycads developed a false fleshy fruits that could be consumed by primitive reptiles that would act as seed dispersers. This process could have intensified the diversification of flowering plants (angiosperms), small mammals and birds during the Cretaceous (65-12MA).

The mutualism can occur in two ways within the seed dispersal by animals.

The first case is carried out by animals that eat seeds or fruits. These seeds or some parts of the fruits (diaspores) are expelled without being damaged, by defecation or regurgitation, allowing the seed germination. In this case, diaspores are carriers of rewards or lures that result very attractive to animals. That is the reason why fruits are usually fleshy, sweet and often have bright colours or emit scents to attract them.

For example, the red-eyed wattle (Acacia cyclops) produces seeds with elaiosomes (a very nutritive substance usually made of lipids) that are bigger than the own seed. This suppose an elevated energy cost to the plant, because it doesn’t only have to produce seeds, as it has to generate the award too. But in return, the rose-breasted or galah cockatoo (Eolophus roseicapillus) transports their seeds in long distances. Because when the galah cockatoo eats elaiosomes, it also ingest seeds which will be transported by its flight until they are expelled elsewhere.

On the left,  Galah  cockatoo (Eolophus roseicapillus) (Autnor: Richard Fisher, flickr) ; On the right, red-eyed wattle’s seeds (black) with the elaiosome (pink) ( Acacia cyclops) (Autnor: Sydney Oats, flickr).

And the other type of seed dispersal by animals that establishes a mutualistic relationship occurs when the seeds or fruits are collected by the animal in times of abundance and then are buried as a food storage to be used when needed. As long as not all seed will be eaten, some will be able to germinate.

A squirrel that is recollecting som nuts (Author: William Murphy, flickr)

But this has not finished yet, since there are other curious and less well-known examples that have somehow made that both animals and plants can live together in a perfect “marriage.” Let’s see examples:

Azteca and Cecropia

Plants of the genus Cecropia live in tropical rain forests of Central and South America and they are very big fighters. The strategy that allow them to grow quickly and capture sunlight, avoiding competition with other plants, resides in the strong relationship they have with Azteca ants. Plants provide nests to the ants, since their stems are normally hollow and with separations, allowing ants to inhabit inside. Furthermore, these plants also produce Müllerian bodies, which are small but very nutritive substances rich in glycogen that ants can eat. In return, the ants protect Cecropia from vines and lianas, allowing them to success as a pioneer plants.

Ant Plants: Cecropia – Azteca Symbiosis (www.youtube.com)

Marcgravia and Bats

Few years ago, an interesting plant has been discovered in Cuba. This plant is pollinated by bats, and it has evolved giving rise to modified leaves that act as satellite dish for echolocation performed by these animals. That is, their shape allow bats to locate them quickly, so they can collect nectar more efficiently. And at the same time, bats also pollinate plants more efficiently, as these animals move very quickly each night to visit hundreds of flowers to feed.

Marcgravia (Author: Alex Popovkin, Bahia, Brazil, Flickr)

In general, we see that the life of plants depends largely on the life of animals, since they are connected in one way or another. All the interactions we have presented are part of an even larger set that make life a more complex and peculiar one, in which one’s life cannot be explained without the other’s life. For this reason, we can say that life of some animals and some plants resembles a marriage.

REFERENCES

• Notes from the Environmental Biology degree (Universitat Autònoma de Barcelona) and the Master’s degree in Biodiversity (Universitat de Barcelona).
• Bascompte, J. & Jordano, P. (2013) Mutualistic Networks (Chapter 1. Biodiversity and Plant-Animal Coevolution). Princeton University Press, pp 224.
• Dansereau, P. (1957): Biogeography: an Ecological Perspective. The Ronald Press, New York., pp. 394.
• Fenner M. & Thompson K. (2005). The Ecology of seeds. Cambridge: Cambridge University Press, 2005. pp. 250.
• Font Quer, P. (1953): Diccionario de Botánica. Editorial Labor, Barcelona.
• Izco, J., Barreno, E., Brugués, M., Costa, M., Devesa, J. A., Fernández, F., Gallardo, T., Llimona, X., Parada, C., Talavera, S. & Valdés, B. (2004) Botánica ªEdición. McGraw-Hill, pp. 906.
• Murray D. R. (2012). Seed dispersal. Academy Press. 322 pp.
• Tiffney B. (2004). Vertebrate dispersal of seed plants through time. Annual Review of Ecology, Evolution and Systematics. 35:1-29.
• Willis, K.J. & McElwain, J.C. (2014) The Evolution of Plants (second edition). Oxford University Press, pp. 424.
• National Geographic (2011). Bats Drawn to Plant via “Echo Beacon”. http://news.nationalgeographic.com/news/2011/07/110728-plants-bats-sonar-pollination-animals-environment/

Evolution for beginners 2: coevolution

After the success of Evolution for beginners, today we’ll continue  knowing the basics of biological evolution. Why  exist insects that seem orchids and vice versa? Why gazelles and cheetahs are almost equally fast? Why your dog understands you? In other words, what is coevolution?

WHAT IS COEVOLUTION?

We know that it is inevitable that living beings establish symbiotic relationships between them. Some depend on others to survive, and at the same time, on elements of their environtment as water, light or air. These mutual pressures between species make that evolve together, and as one evolve as a species, in turn it forces the other to evolve. Let’s see some examples:

POLLINATION

The most known process of coevolution is pollination. It was actually the first co-evolutionary study (1859) by Darwin, although he didn’t use that term. The first to use the word coevolution were Ehrlich and Raven (1964).

Insects existed long before the appearance of flowering plants, but their success was due to the discovery that nectar is a good reserve of energy. In turn, the plants found in the insects another way more effectively to carry pollen to another flower. Pollination by the wind (anemophily) requires more production of pollen and a good dose of luck to at least fertilize some flowers of the same species. Many plants have developed flowers that trap insects until they are covered with pollen and then set them free. These insects have hairs in their body to enable this process. In turn some animals have developed long appendages (beaks of hummingbirds, butterflies’ proboscis…) to access the nectar.

Darwin’s moth (Xantophan morganii praedicta). Photo by Minden Pictures/Superstock

It is the famous case of the Darwin’s moth (Xanthopan morganii praedicta) of which we have already talked about. Charles Darwin, studying orchid Christmas (Angraecum sesquipedale) saw that the nectar was 29 cm inside the flower. He sensed that there should exist an animal with a proboscis of this size. Eleven years later, Alfred Russell Wallace reported him that the Morgan’s sphinxs had proboscis over 20 cm long, and a time later they were found in the same area where Darwin had studied that species of orchid (Madagascar). In honor of both it was added “praedicta” to the scientific name.

There are also bee orchids that mimic female insects to ensure their pollination. To learn more about these orchids and the Christmas one, do not miss this post by Adriel.

The bat Anoura fistulata and its long tongue. Photo by Nathan Muchhala

But many plants not only depend on insects, also some birds (like humming birds) and mammals (such as bats) are essential to pollination. The record for the longest mammal tongue in the world is for a bat from Ecuador (Anoura fistulata); its tongue measures 8 cm (150% of the length of its body). It is the only who pollinates one plant called Centropogon nigricans, despite the existence of other species of bats in the same habitat of the plant. This raises the question of whether evolution is well defined, and occurs between pairs of species or it is diffuse due to the interaction of multiple species.

PREDATOR-PREY RELATIONSHIPS

The cheetah (Acinonyx jubatus) is the fastest vertebrate on land (up to 115 km/h). Thomson’s gazelle (Eudorcas thomsonii), the second (up to 80 km/h). Cheetahs have to be fast enough to catch a gazelle (but not all, at risk of disappearing themselves) and gazelles fast enough to escape almost once and reproduce. The fastest gaelles survive, so nature selects in turn faster cheetahs, which are who eat to survive. The pressure from predators is an important factor that determines the survival of a population and what strategies should follow the population to survive. Also, the predators will find solutions to possible new ways of life of their prey to succeed.

Cheetah hunting a Thomson’s gazelle in Kenya. Photo by Federico Veronesi

The same applies to other predator-prey relationships, parasite-host relationships, plants-herbivores, improving their speed or other survival strategies like poison, spikes…

HUMAN AND DOGS … AND BACTERIA

Our relationship with dogs since prehistoric times, it is also a case of coevolution. This allows, for example, to create bonds with just looking at them. If you want more information, we invite you to read this post where we talk about the issue of the evolution of dogs and humans in depth.

Another example is the relationship we have established with the bacteria in our digestive system, essential for our survival. Or with pathogens: they have co-evolved with our antibiotics, so using them indiscriminately has favored these species of bacteria to develop resistance to antibiotics.

THE IMPORTANCE OF COEVOLUTION

Coevolution is one of the main processes responsible for the great biodiversity of the Earth. According to Thompson, is responsible for the millions of species that exist instead of thousands.

The interactions that have been developed with coevolution are important for the conservation of species. In cases where evolution has been very close between two species, if one become extint will lead to the extinction of the other almost certainly. Humans constantly alter ecosystems and therefore biodiversity and evolution of species. Just declining one species, we are affecting many more. This is the case of the sea otter (Enhydra lutris), which feeds on sea urchins.

Sea otter (Enhydra lutris) eating sea urchins. Photo by Vancouver Aquarium

Being hunted for their fur, urchins increased number, devastated entire populations of algae (consumer of CO2, one of the responsible of global warming), seals who found refuge in the algae nonexistent now were more hunted by killer whales… the sea otter is therefore a key species for the balance of this ecosystem and the planet, as it has evolved along with urchins and algae.

Coevolutive relations between flowers and animals depend on the pollination of thousands of species, including many of agricultural interest, so we must not lose sight of the seriousness of the issue of the disappearance of a large number of bees and other insects in recent years. A complex case of coevolution that directly affects us is the reproduction of fig.

TO SUMMARIZE

As we have seen, coevolution is the evolutionary change through natural selection between two or more species that interact reciprocally.

It is needed:

• Specificity: the evolution of each feature of a species is due  to selective pressures of the feature of the other species.
• Reciprocity: features evolve together.
• Simultaneity: features evolve simultaneously.

REFERENCES

• Massa R (2007). Atlas ilustrado del origen de la vida: La evolución de las especies. Jaca Book spa, Milano.
• Muchhala N. Nectar bat stows huge tongue in its rib cage. Nature (2006) vol. 444 (7120) pp. 701-702
• Coevolución: patrones y procesos
• Celebrando a Darwin
• Los 10 mamíferos más rápidos de la tierra
• La coevolución y las enseñanzas de Darwin
• Coevolución
• Las nutrias marinas pueden salvar nuestro planeta

The fig and its reproduction

Has anyone ever seen a fig flower? Surely even if you really look for it, you will not find any of them. In fact, neither Linnaeus, the great Swedish botanist, could discover the enigma of fig flowers and when he described the species and gave him a scientific name (Ficus carica L.), he said the fig had no flowers! But then how does the fig reproduce himself and origins its delicious summer fruit; the fig?

A CASE OF OBLIGATE MUTUALISM

The flowers of the fig tree cannot be seen as they grow hidden inside the receptacle that supports them, the fig. They have developed a close relationship of mutualism with their pollinators so they don’t need to bloom externally offering sweet rewards. Indeed, each species of Ficus (including 750 species in family Moraceae) is pollinated by a unique wasp species (family Agaonidae; Blastophaga psenes in the case of the Mediterranean fig). It is a very complex case of coevolution between a plant and its pollinator in which neither species could survive without the other.

The mechanism of fig pollination works as a perfect gear. Female wasps are the first to visit the fig, where they arrive attracted by the smell of the mature female flowers. The female wasps possess special adaptations to penetrate the fig and achieve their ultimate goal: to leave their eggs inside. They have inverted teeth in the jaws and special hooks in the legs that let them to advance into the fruit. However, they have only one opportunity to deposit their eggs since most wasps lose their wings and antennae once they have entered the fig and therefore can no longer look for another. Once the eggs hatch, the wasp larvae feed on the contents of the fig. The male wasp larvae are the first to complete its development and when they reach sexual maturity, they seek female wasps, fertilize them and die inside the fig. The female wasps leave the figs a few days later, coinciding with the male flowers maturation and thus favoring that their exit will be carrying pollen. These fertilized and full of pollen wasps will look for a fig fruit again where to leave the pollen and eggs. Then the cycle begins again.

Open fig with its pollinator wasp (Foto: Royal Society Publishing).

IS IT THE FIG ACTUALLY A FRUIT?

The fig is actually an infructescence (an ensemble of fruits that act as a single unit to facilitate the dispersion) with a special morphology called syconium. The syconium is a type of pear-shaped receptacle, thickened and fleshy with a small opening, the ostiole, that allows the entry of pollinators. Both male and female flowers (fig is monoecious) are together in the syconium, enveloped by bracts (white filaments found in the fig), but each one maturates in different time to avoid autopollination. Once the flowers are fertilized, the fruits originate within the same structure, thus flowers and fruits mix up.

Fig with the ostiole, hole by which wasps get into the flowers (Foto: barresfotonatura)

WHERE DO THE FIGS COME FROM?

Who would have said that the fig tree would have a so complex fructification mechanism? In fact, the fig tree is native to Asia but is now naturalized in the Mediterranean since prehistoric times. There is evidence of its consumption and cultivation from the Neolithic. The fig tree is considered as one of the first plants cultivated by mankind. In spring it produces fertilized figs (breba), increasing its production with two harvests per year.

Eivissa‘s fig tree (Ficus carica; Foto: barresfotonatura)

Main Ficus species grow in tropical climates. In temperate areas, some of this species were brought for its interest in gardening. Many cities have grown these giants in their public gardens because their dramatic appearance. They can reach up to 30 meters high and they develop aerial roots that end up reaching the ground acting as buttress that hold their weight. The have become unique elements of our urban landscape; such as in the Parque Genovés, Cadiz or the magnificent specimen of Ficus rubiginosa located in the Botanic Garden of Barcelona.

Ornamental fig tree at the Parque Genovés, Cadiz (Foto: barresfotonatura)

Ficus socotrana with aerial roots in Ethiopia (Foto: barresfotonatura)

REFERENCES

• Byng W (2014). The Flowering Plants Handbook: A practical guide to families and genera of the world. Plant Gateway Ltd., Hertford, UK.
• Cruaud A, Cook J, Da-Rong Y, Genson G, Jabbour-Zahab R, Kjellberg F et al. (2011). Fig-fig wasp mutualism, the fall of the strict cospeciation paradigm? In: Patiny, S., ed., Evolution of plant-pollinator relationships. Cambridge: Cambridge University Press, pp. 68–102.
• Font Quer P (1953). Diccionario de Botánica. Ed. Labor
• Machado CA, Robbins N, Gilbert MTP & Herre EA (2005). Critical review of host specificity and its coevolutionary implications in the fig/fig-wasp mutualism. Proceedings of the National Academy of Sciences of the USA 102: 6558–6565.
• Ramirez WB (1970). Host specificity of fig wasps (Agaonidae). Evolution 24: 680–691.
• Serrato A & Oyama K (2012). Ficus y las avispas Agaonidae. ContactoS 85: 5–10.

Migration in danger! The disappearance of the monarch butterfly

Generally, we tend to think of migration as an event exclusively linked to complex organisms (like mammals or birds). But there are always exceptions: the North American populations of the monarch butterfly (Danaus plexippus) cover a distance of almost 5000km (more than some complex animals!) in order to reach their hibernation areas, where there can be concentrated thousands of specimens during the winter. Unfortunately, the migration phenomenon depend on many factors that are being damaged by anthropogenic pressure nowadays, so that the future of these populations and also their migration are in danger.

Throughout this article, you will learn some of the most curious biology traits of these organisms, the main causes that could be endangering their populations and the consequences that this would entail.

INTRODUCTION

The monarch butterfly (Danaus plexippus) is a butterfly of the Nymphalidae family. It’s also probably one the most well-known butterflies of North America due to its long migration, that their specimens perform from the north of EEUU and Canada to California coast and Mexico, covering a distance of almost 5000km to reach their hibernation areas. It’s, by far, the insect that performs the widest and large migration of all.

Specimen of monarch butterfly (Danaus plexippus) with its typical color pattern: white, black and orange (Picture by Peter Miller on Flickr, Creative Commons).

Although the North American populations of this species are the most known worldwide due to their migration pattern, there are also monarch butterflies in some Atlantic islands (Canary islands, Azores and Madeira), and sometimes also as eventual migrators that reach the coasts of Western Europe (United Kingdom and Spain). Moreover, they were introduced in New Zealand and Australia during the XIX century.

LIFE CYCLE

The life cycle of this species is very unique. First of all, they’re considered specialist butterflies: they lay their eggs exclusively over plants of the Asclepias genus (also known as milkweeds), and their newborn caterpillars (which are black, white and yellow striped) feed only on these plants. This is a very interesting fact, because the plants of this genus contain cardiac glycosides that are progressively assimilated by the caterpillar tissues, which let them to acquire a disgusting taste that prevents them to be predated. This taste will last during their adult phase.

Caterpillar of a monarch butterfly (Picture by Lisa Brown on Flickr, Creative Commons).

Once completed the larva phase, the metamorphosis take place so that the caterpillars become adult butterflies colored in black, white and orange. Both caterpillar and butterfly color patterns carry out a communicative function: it’s a mechanism to warn other animal of their toxicity, fact which is known as aposematic mimicry (this phenomenon is very frequent in a lot of group of animals, even in mammals).

Phases of the metamorphosis of the monarch butterfly (Picture by Steve Greer Photography).

The adult phase also has some particularities: during the mating season (April-August) some generations of adults are generated, and each of them has a life expectancy of a few weeks, more or less. Then, an awesome event takes place: the butterflies of the generation born at the end of August (when temperatures get low and days became shorter) stops the maturing process of their reproductive organs (phenomenon known as diapause) so they can spend their energy on enlarging their life expectancy to 9 months. This generation is known as “Methuselah generation” due to its longevity.

The increase of their longevity allows this generation to cover the long distance required to reach the hibernation areas during the autumn (Mexico and California coast) and then to come back to the north of America at the end of the winter.

Hundreds of monarch butterflies flying over the place called ‘El Santuario ‘El Rosario” (Mexico) (Picture by Luna sin estrellas on Flickr, Creative Commons).

A ROUND TRIP: THE GREAT MIGRATION

Although the monarch butterfly isn’t only located in North America, there is no evidence nowadays showing that the other populations of monarch butterflies do such a long migration. It’s believed that the fact that only these populations of butterflies go on a trip this long is due to the wide spreading of plants of the Asclepias genus over all North America that took place in the past. Scientists suggest this event allowed the monarch butterflies to spread progressively to the south.

WHICH PLACES DO THE BUTTERFLIES VISIT?

A migration is always a complex process. In this case, the migration to the south is divided into two simultaneous migrations:

• The east migration: this trip is made by those butterflies that fly from the east of the Rocky Mountains, South of Canada and a big part of USA to the central part of Mexico (90% of all the monarch butterflies located in North America go on this trip).
• The west migration: this trip is made by those butterflies that fly from the west of the Rocky Mountains, South of Canada and a little part of USA to the California coast (10% of all the monarch butterflies located in North America go on this trip).

Migratory patterns of the monarch butterfly in North America (round trip) (Sources: Monarchwatch.org y Monarch Alert).

Once in the winter habitats, the butterflies plunge into a lethargic state until the next spring, when they become sexually active and start mating before heading again to the north.

It’s a very surprising event seeing all the butterflies sleeping together and covering all the plants and trees of the winter habitats!

Thousands of butterflies gather over the vegetation (Picture by Carlos Adampol Galindo on Flickr, Creative Commons).

PROTECTED AREAS

There exists a lot of protected areas all over the places where the butterflies go through.

One of the most important protected areas is the Monarch Butterfly Biosphere Reserve (Mexico City), which is considered a World Heritage Site by the UNESCO since 2008.

Monarch Butterfly Biosphere Reserve (Picture by Michelle Tribe on Flickr, Creative Commons).

And why are these butterflies so protected? Besides the fact that their migration pattern is considered an incredible phenomenon, they are pollinators that contribute to the pollination of the wild flora and also of the crops of North America.

THE ‘QUEEN’ IS IN DANGER!

Although there exists a huge effort to protect them, the migratory phenomenon of the North American monarch butterflies is in danger nowadays due to the anthropic pressure, which could also put their populations at risk in the future.

According to the data generated by the WWF, the surface of the winter habitats occupied by these butterflies has decreased 94% in 10 years, going from 27,48 acres occupied in 2003 to only 1,65 acres in 2013. This is the lower value registered in the last 20 years.

Decresing of the surface occupied by the monarch butterflies in the winter habitats (Data form WWF website).

Even though the surface occupied by these organisms has been fluctuating over the years as a part of a natural process, this pronounced decreasing that has taken place in only a few years suggests that butterflies are stopping their annual migrations to the south.

Total occupied area by the butterflies in their winter habitats since 1993 to 2013 (WWF-Telcel-CONANP).

This recession has also been registered in other species of butterflies at different emplacements all over the world, so there must exist some kind of factor in common with the ones affecting the North American monarch butterfly populations.

WHAT COULD BE THE MAIN CAUSES OF THIS RECESSION?

According to the WWF, the main causes that could being putting in danger the migration process of the monarch butterflies are:

• The reduction of the surface occupied by plants of the Asclepias genus: as we said above, the caterpillars feed exclusively on these plants. But the use of certain herbicides and the changes on the rain patterns could being limiting their dispersal over a big part of North America.
• Deforestation: cutting down trees massively and the subsequent desertization could being reducing their winter habitats.
• Extreme climate: the global change, which entails changes in temperature and rain patterns, could being putting at risk the survival of adult butterflies, preventing them to reach the longevity required to carry out complete migrations.

WHICH EFFORTS ARE MADE TO PROTECT THESE POPULATIONS?

As I said above, monarch butterflies are an essential part of the pollination net of North America and also iconic insects, so there exists a big interest on protecting them.

Nowadays, most of the protected areas of North America are making a big effort to improve the quality of their habitats. Among them, the Monarch Butterfly Biosphere Reserve (Mexico) along with the WWF are trying to restore the woods where butterflies hibernate and also promoting a sustainable tourism (enter this link to see more information).

 .            .            .

The case of the monarch butterfly is only one of a huge list of animals in danger. Nowadays, a lot of animals with complex migration patterns and wide spreading areas are suffering similar pressures, mostly of them with an anthropogenic origin. There’s still so much work to do, and it depends on all of us.

REFERENCES

• WWF – Monarch Butterfly
• Soymonarca.mx
• Monarch Butterfly information
• Monarch Butterfly Fundation
• Scientific American – “Monarch butterflies Could Gain Endangered Species Protection”
• CBC News – “Why the monarch butterfly migration may be endangered”

• National Geographic – “Migrating Monarch Butterflies in “Grave Danger,” Hit New Low“

Main picture by Carlos Adampol Galindo on Flickr.

If the nymphs were plants, they would be water lilies

This week, I’m going to introduce water lilies, some flowers very nice and known for being important in the ornamentation.

INTRODUCTION

The Nymphaeaceae family has few species and most of them are freshwater aquatic plants in quiet places and commonly are known as water lilies. Because they are aquatic plants, the family’s name is derived from the Latin word nympha, as they have some similarity with nymphs, mythological beings with a predilection for the waters.

Water nymphs, water lilies can be seen around (Painting by Henrietta Rae, 1909).

The water lilies were originated in warm regions, but they are now subcosmopolitan and can be found in several parts of the world, living in ponds, lakes and freshwater streams.

MORPHOLOGICAL CHARACTERS

The water lilies are perennial aquatic plants, they live several years, and are rhizomatous, that is, they have a thickened stem below the soil at the bottom of the water. In some species, we see that some leaves are immersed and others are floating on the water surface, being sometimes even membranous (they have raised edges perpendicularly upward to avoid the ingress of too much water). When this morphological difference happens, we talk about heteromorphous leaves.

Water lily's membranous leaves (Victoria amazonica) (Photo taken by Dirk van der Made).

Their flowers grown out of water and are constituted by a variable number of sepals, petals and stamens, which are helically born. Therefore, flowers are acyclic, that is, are asymmetrical or irregular because they have no symmetric plane. These flowers are solitary, not born grouped, and hermaphrodites, that is, both male (stamens) and female (ovary) sex organs occur in the same flower.

Pygmy waterlily (Nymphaea tetragona)(Photo taken by Miguel303xm).

These perianth parts (petals and sepals) and stamens are free among them, therefore, they are not united or fused among them, and normally appear in large numbers. The stamens are different to several of other flowers, because they are laminar stamens, similar to the petals. Therefore, they are not filamentous, are thicker and wider.

DIVERSITY

Currently, the genera of water lilies which have more relevance are Nuphar, Nymphaea and Victoria, but there are also some others. Below I present some cases of very interesting species.

The tiger lotus or Egyptian white water-lily (Nymphaea lotus) is native of the Nile Valley and eastern Africa. It is prized as an ornamental and ancient Egyptians believed that the flower could give strength and power.

Egyptian white water-lily (Nymphaea lotus) (Photo taken by Meneerke bloem).

The yellow water-lily (Nuphar lutea) is typical of Europe, North Africa and the Middle East and, as the previous one, is also very ornamental. Furthermore, it has been long used in traditional medicine. Its roots were applied on the skin and seeds and roots were eaten to treat different diseases.

Yellow water-lily (Nuphar lutea) (Photo taken by Oksana Golovko).

Finally, I’d want to introduce the genus of Victoria, whose pollinitation is very curious. It has two American species: V. cruziana in Argentina and V. amazonica in the Amazon and Brazil. Plants of this genus are very big, with floating leaves reaching to 2 meters in diameter and with showy flowers which can reach up to 30 centimeters and are opened at evening.When these flowers are opened, strong scents and a little heat are released and with the whitish and beige colours of the petals, they result very attractive to the beetles (Coleoptera) that are feed of starch extensions on the flowers (starch bodies). The next morning, flowers are closed and the beetles are captured within, causing them to be permeated of pollen. At afternoon, flowers are reopened and allow beetles to escape. Then, as the flowers have been pollinated, their colour varies to pink and they also lose scent. Therefore, the beetles feel more attracted to white flowers that have not been pollinated yet. Finally, the pink flowers are dipped.

On the left, V. cruziana (Photo taken by Greenlamplady); On the right, V. amazonica (Photo taken by frank wouters).

IMPORTANCE

Currently, several species are used as ornamentals, decorative. Furthermore, the water lilies can also be used to get food; the seeds and rhizomes of the genera Nymphaea and Victoria are edible. On the other hand, a very curious thing is that the nerves of the leaves of some species have been used to extract a liquid, which has been applied to treat snake bites.

I hope you liked the way the water lilies behave and all their tales and uses that are associated to them, although only for its beauty are charming. If you enjoyed, do not forget to share in different social networks. Thanks for your interest.

REFERENCES

• Bolòs, J. Vigo, R. M. Masalles & J. M. Ninot. 2005. Flora manual dels Països catalans. 3ed. Pòrtic Natura, Barcelona: pp. 1310.
• Notes of Botany and Phanerogamae, Degree of Environmental Biology, UAB.
• http://www.biologia.edu.ar/diversidadv/fascIII/11.%20Nymphaeaceae.pdf
• http://www.thecompositaehut.com/www_tch/webcurso_spv/familias_pv/nymphaeaceae.html
• http://web.ing.puc.cl/~ing1004/Homeworks/SeresVivos_E3/g63_Sof%C3%ADaGjuranovic_VictoriaAmaz%C3%B3nica.pdf

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The secret life of bees

If we talk about bees, the first thing that comes to mind might be the picture of a well-structured colony of insects flying around a honeycomb made of perfectly constructed wax cells full of honey.

But the truth is that not all bees known nowadays live in hierarchical communities and make honey. Actually, most species of bees develop into a solitary life-form unlike the classical and well-known honey bees (which are so appreciated in beekeeping).

Through this article, I’ll try to sum up the different life-forms of bees in order to shed light on this issue.

INTRODUCTION

Bees are a large diverse group of insects in Hymenoptera order, which also includes wasps and ants. To date, there are up to 20,000 species of bees known worldwide, although there could be more unidentified species. They can be found in most habitats with flowering plants located in every continent of the world (except for the Antarctica).

Bees pick up pollen and nectar from flowers to feed themselves and their larvae. Thanks to this, they contribute on boosting the pollination of plants. Thus, these insects have an enormous ecological interest because they contribute to maintain and even to enhance flowering plant biodiversity on their habitats.

Specimen of Apis mellifera or honey bee (Picture by Leo Oses on Flickr)

However, even though the way they feed and the sources of food they share could be similar, there exist different life-forms among bees which are interesting to focus on.

BEE LIFE-FORMS

SOLITARY BEES (ALSO KNOWN AS “WILD BEES”)

Most species of bees worldwide, contrary to the common knowledge, develop into a solitary life-form: they born and grow alone, they mate once when groups of male and female bees meet each other and, finally, they die alone too. Some solitary bees live in groups, but they never cooperate with each other.

Female of solitary life-form bees build a nest without the help of other bees. Normally, this kind of nest is composed by one or more cells, which are usually separated by partition walls made of different materials (clay, chewed vegetal material, cut leaves…). Then, they provide these cells with pollen and nectar (the perfect food for larvae) and, finally, they lay their eggs inside each cell (normally one per cell). Contrary to hives, these nests are often difficult to find and to identify with naked eyes because of its discreetness.

Solitary bee nest. In this picture we can see the partition walls, pollen and eggs inside each cell (Picture from USDA).

The place where solitary bees build their nest is highly variable: underground, inside twisted leaves, inside empty snail shells or even inside pre-established cavities made by human or left behind by other animals.

These bees don’t make hives nor honey, so these are probably the main reasons because of what they are less popular than honey bees (Apis mellifera). Although solitary bees are the major contributors on pollination due to their abundance and diversity (some of them are even exclusive pollinators of a unique plant species, which reveals a close relation between both organisms), most of the studies related with bees are focused on honey bees, because of what studies and protection of these solitary life-forms still remain in the background.

There exists a large diversity of solitary bees with different morphology:

1) Specimen of Andrena sp. (Picture by kliton hysa on Flickr). 
2) Specimen of Xylocopa violacea or violet carpenter bee (Picture by Nora Caracci fotomie2009 on Flickr).
3) Specimen of Anthidium sp. (Picture by Rosa Gambóias on Flickr).

There are also parasite life-forms among solitary bees, that is, organisms that benefit at the expense of another organism, the host; as a result, the host is damaged in some way. Parasitic bees take advantage of other insects’ resources and even resources from other bees causing them some kind of damage. This is the case of Nomada sp. genus, whose species lay their eggs inside other bee nests (that is, their hosts), so when they hatch, parasite larvae will eat the host’s resources (usually pollen and nectar) leaving them without food. Scientists named this kind of parasitism as cleptoparasitism (literally, parasitism by theft) because parasitic larvae steal food resources from the host larvae.

Specimen of Nomada sp. (Picture by Domingo Roldan on Flickr)

PSEUDOSOCIAL BEES

From now on, we are going to stop talking about solitary bees and begin to introduce the pseudosocial life-forms, that is, bees that live in relatively organized and hierarchical groups which are less complex than truly social life-forms, also known as eusocial life-forms (which is the case of Apis mellifera).

Probably, the most famous example is the bumblebee (Bombus sp.). These bees live in colonies in which the queen or queens (also known as fertilized females) are the ones who survive through the winter. Thus, the rest of the colony dies due to cold. So is thanks to the queen (or queens) that the colony can arise again the next spring.

Specimen of Bombus terrestris or buff-tailed bumblebee(Picture by Le pot-ager "Je suis Charlie" on Flickr).

EUSOCIAL BEES

Finally, the most evolved bees known nowadays in terms of social structure complexity are eusocial bees or truly social bees. Scientist have identified only one case of eusocial bee: the honey bee or Apis mellifera.

Since the objective of this article was to refute the “all bees live in colonies, build hives and make honey” myth, I will not explain further than the fact these organisms form complex and hierarchical societies (this constitutes a strange phenomenon which has also been observed in thermites and ants) normally led by a single queen, build large hives formed of honeycombs made of wax, and make honey, a very energetic substance highly appreciated by humans.

Specimens of Apis mellifera on a honeycomb full of honey (Picture by Nicolas Vereecken on Flickr).

As we have been seeing, solitary bees play an important role in terms of pollination, because of what they must be more protected than they currently are. However, honeybees, and not solitary bees, still remain being on the spotlight of most scientists and a great part of society because of the direct resources they provide to humans.

REFERENCES

• Notes taken during my college practices at CREAF (Centre de Recerca Ecològica i d’Aplicacions Forestals – Ecological Research and Forest Applications Centre). Environmental Biology degree, UAB (Universitat Autònoma de Barcelona).
• O’toole, C. & Raw A. (1999) Bees of the world. Ed Blandford
• Pfiffner L., Müller A. (2014) Wild bees and pollination. Research Institute of Organic Agriculture FiBL (Switzerland).
• Solitary Bees (Hymenoptera). Royal Entomological Society: http://www.royensoc.co.uk/insect_info/what/solitary_bees.htm
• Stevens, A. (2010) Predation, Herbivory, and Parasitism. Nature Education Knowledge 3(10):36

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