Arxiu d'etiquetes: insect

Some insects and other arthropods you should not confuse

Untrustworthy and sensational news about insects and arthropods are constantly shared through social networks, spreading tergiversated data and confusing amateur users. As a result, this usually leads to misidentifications and unnecessary alarmism toward harmless organisms.

Here we bring you a brief list of some insects and other arthropods that are usually confused and how to tell them apart. Don’t get tricked!

Spiders VS ‘Anything resembling them’

Spiders (Order Araneae) probably are some of the most feared arthropods among users for two main reasons: they are venomous and there are a lot of other arachnids that resemble them. So, it is quite understandable some people have serious doubts when finding an organism with eight long legs and a grim face.

However, most of these spider-like organisms are harmless and  unable to weave webs:

Harvestmen: unlike other arachnids, harvestmen or daddy longlegs (Order Opiliones) don’t have their body divided into two parts (prosoma and opisthosoma) by a thin waist, so they remind off a ‘ball with legs’. Also, they only have a pair of central eyes very close to each other. They neither have venom glands nor silk glands, so they can’t bite nor weave webs. They live in moist places, caves and near to streams and harvests. They are usually confused with spiders of the Pholcidae family because of their long legs.

Pholcus phalangioides (Pholcidae) (Picture by Olaf Leillinger, CC 2.5)

Harvestman (Picture by Dalavich, CC 3.0)

Solifugae: also known as camel spiders, Solifugae is an order of tropical arachnids characterized for having a segmented body and a pair of conspicuously large chelicerae forwardly projected. However, and despite their menacing appearance, they aren’t venomous (even though they bite can be very painful) nor weave webs. They inhabit desert and arid places, some of them are nocturnal and the diurnal ones move quickly looking for shadows to escape from sunlight.

Camel spider (Picture by Swen Langel, CC 2.0).

Amblypygi: also known as whip spiders or tailless whip scorpions, Amblypygi is an order of tropical arachnids that are neither spiders nor scorpions. Despite their menacing appearance, as it happens with camel spiders, whip scorpions don’t have venom glands. They have a pair of big thorny pedipalps ended in a pincer for grabbing preys, while the first pair of legs, which are filiform and segmented, act as sensory organs (not for walk). They don’t weave webs and have nocturnal habits.

Amblypygi (Picture by José Eugenio Gómez Rodríguez on Flickr, CC 2.0)

Pill bugs VS Pill millipedes

When playing in a park or in some natural place as a kid, you some time probably found a small animal, full of legs that rolled up when being touched.

These organisms are commonly known as woodlice. Woodlice belong to the suborder Oniscidea, a group of terrestrial crustaceans within the order Isopoda. They have a tough, calcarean and segmented exoskeleton, and inhabit moist places.

Armadillidium vulgare, Oniscidea (Picture by Franco Folini, CC 2.5)

Woodlice of the family Armadillidae, also known as pill bugs, are usually confused with pill millipedes (Subphylum Myriapoda, Class Diplopoda, Superorder Oniscomorpha), both groups with a similar external appearance and able to roll up into an almost perfect sphere as a defensive mechanism (convergent evolution).

Glomeris marginata, Oniscomorpha (Picture by Stemonitis, CC 2.5).

To tell them apart, you have to count the total number of legs per segment: if it has only a pair of legs per segment (one at each side of the segment), it is a pill bug; if it has two pairs, it is a pill millipede.

Bees and wasps VS Hoverflies

We talked widely about the main differences between bees and wasps (Order Hymenoptera) in this postThis time, we introduce you the hoverflies or syrphid flies (Order Diptera, Suborder Brachycera, Family Syrphidae), which resemble a lot to bees and wasps.

Resemblance of hoverflies to bees, wasps and bumblebees is a clear example of Batesian mimicry, which we explained widely in this post about animal mimicry. Moreover, hoverflies mimicry goes even further, since some of them also imitate the flight and the hum of these hymenopterans.

Hoverfly (Public domain picture, CC0).

Honey bee (Picture by Andy Murray on Flickr, CC 2.0)

To tell them apart, you have to pay attention to their eyes, antennae and wings: since they are flies, hoverflies have a pair of big compound eyes that occupy almost all their head, very short antennae with eight or less segments and a single pair of wings (the second pair has evolved into small equilibrium organs, the halteres), while wasps, bees and bumblebees have smaller compound eyes that occupy only the sides of the head, longer antennae with ten or more segments and two pairs of functional wings. Moreover, female hoverflies don’t have the abdomen ended in a stinger, so they are completely harmless.

Ladybugs VS Pyrrhocoris apterus

If you look for ladybugs pictures on Internet, you’d probably find a picture of this insect:

Public domain picture (CC0)

This is Pyrrhocoris apterus, a very common insect in the Palearctic area (from Europe to China) and recorded to the USA, Central America and India. You can find it on common mallows (Malva sylvestris), from which they eat seeds and sap, and they usually congregate in big groups because of their gregarious behavior.

Ladybugs are coleopterans (Order Coleoptera) with a more or less globular shape; they are carnivorous (with a diet based mainly on the intake of aphids) and can fly. Their first pair of wings are hard (elytra) and form a kind of shield that encloses the second pair of membranous wings.

Ladybug Coccinella septempunctata (Public domain picture, CC0)

On the other hand, Pyrrhocoris apterus is a bug (Order Heteroptera) with a depressed body, phytophagous habits and, unlike ladybugs and other bugs, it is unable to fly. Moreover, it doesn’t have a hardened shield.

Mantises VS Mantidflies

Mantises (Order Dyctioptera), which were widely addressed in this post, are very alike to this insect:

Mantispa styriaca (Picture by Gilles San Martin on Flickr, CC 2.0)

This insect belongs to the family Mantispidae (Order Neuroptera), also known as mantidflies or mantispids. This group is very well represented in tropical and subtropical countries, and just a few species are known from Europe. They have a pair of raptorial legs like those of Mantodea which they use for grabbing their preys.

Neuropterans, like mantidflies, green lacewings and antlions, have two pairs of similar sized wings with a very complex and branched venation. In Mantodea, the first pair of wings are smaller and harder than the second one, which are membranous and functional for flying; also, this second pair doesn’t have such a complex venation like that of neuropterans.

Mantodea (Picture by Shiva shankar, CC 2.0)

Mantidflies of the genera Climaciella and Entanoneura have a body coloration like that of some wasps, but they are totally harmless.

Climaciella brunnea (Picture by Judy Gallagher on Flickr, CC 2.0)

Mosquitoes VS Crane flies

Have you ever seen a giant mosquito and dreaded its bite? Well, you can stop being afraid of it.

These giant ‘mosquitoes’ (Order Diptera), which are commonly known as crane flies or daddy longlegs (Family Tipulidae), are totally inoffensive (and somewhat clumsy). They are distributed all over the world and inhabit moist places, like meadows and streams. Adults feed on nectar or don’t feed; in any case, they don’t suck blood!

Females have the abdomen ended in a kind of stinger; however, it is only their sharp ovipositor (not a stinger like those of bees or wasps).

Female crane fly (Picture by Irene Lobato Vila)

Dragonflies VS Damselflies

Both groups belong to the Order Odonata and have very similar appearance and behavior, being very common near sitting waters and lakes.

Two thirds of the Odonata are dragonflies (suborder Anisoptera), while the other third are damselflies (suborder Zygoptera). An easy way to tell them apart is by paying attention to their wings at rest: in dragonflies, wings are held flat and away from the body, while in damselflies they are held folded, along or above the abdomen.

On the other hand, eyes of dragonflies are large and touch in the vertex of the head, of which they occupy most of its surface, while those of dragonflies are smaller and are usually located on the sides of the head.

Dragonfly (Public domain image, CC0)

Damselfly (Picture by Xosema, CC 4.0)

.         .         .

If you know about any other insect or arthropod that can be confused, let us know it by leaving a comment!

References

Check the evolution in your own body

42% of the US population and 11.5% of the Spanish people do not believe in evolution. However, there are different evidence that Darwin was right, some of them in your own body. Have you had your appendix or wisdom teeth removed? Find out in this post which vestigial organs you have inherited from your ancestors.

WHAT ARE VESTIGIAL STRUCTURES?

Vestigial structures (often called organs althouth they are not organs properly) are body parts that have been reduced or have lost its original function during the evolution of a species. They can be found in many animals, including humans.

Esqueleto de orca en el que se observan vestigios de las extremidades traseras. Foto: Patrick Gries
Orca skeleton in which vestiges of the hind limbs can be seen. This is a proof of its terrestrial origins. Photo: Patrick Gries

Vestigial structures were fully functional in the ancestors of these species (and in the homologous structures of other existing species), but currently its function is practically useless or it has changed. For example, the second pair of flying wings in some insects such as flies have lost their function and they have been reduced to balance organs (halteres). If you want to know more about the evolution of flight in insects click here.

Besides physical structures, vestigial features can also manifest itself in behavior or biochemistry processes.

WHY ARE THEY  EVIDENCE OF EVOLUTION?

Natural selection acts on species favoring features that increase their survival and eliminating the ones with no benefits, for example when changes appear in the habitat. Individuals with unfavorable characteristics will die or will breed less and that feature will be removed after some generations, while favorable traits will remain as their carriers can pass them to the next generation.

Sometimes there are features that are neither favorable nor unfavorable, so they continue appearing in the next generations. But all has a cost structure (energy, risk to become infected, develop tumors…), so selective pressure continues acting to eliminate something that is not conducive to the success of the species. This is the case of vestigial structures, which “take longer” disappear throughout evolution. Their existence reveal that in the past these structures had an important role in our ancestors.

FIND YOUR VESTIGIAL TRAITS

THE NICTITATING MEMBRANE

We talked about it in How animals see the world. The third eyelid is a transparent or translucent membrane that protects and moisten the eye without losing visibility. It is common in amphibians, reptiles and birds. Among primates, it is only functional in lemurs and lorises.

membrana nictitante, nictitating membrane
Nictitating membrane or third eyelid of a masked lapwing (Vanellus miles). Photo: Toby Hudson

In humans the plica semilunaris is a remnant of the nictitating membrane. Obviously we can not move it but still has some lacrimal drainage function and helps on the eye movement (Dartt, 2006).

Plica semilunaris (pliegue semilunar). Foto: desconocido
Plica semilunaris. Photo: unknown

DARWIN’S TUBERCLE AND EAR MUSCLES

10% of the population has a thickening in the ear, a vestige of the common pointy ear in primates. This structure is called Darwin’s tubercle and has no function.

Variabilidad del Tubérculo de Darwin en la punta de la oreja (0= ausente). Puede presentarse en otras zonas del pabellón auditivo: ver publicación.
Variability of Darwin’s tubercle at the top of the ear (0 = absent).  Credit.

Comparación entre la oreja de un macaco y la nuestra. Fuente
Comparison between the ear of a yellow baboon (Papio cynocephalus) and ours. Credit

Also, primates (and other mammals) have mobile ears to lead the pinna toward the sound source: surely you have noticed it in your house dog or house cat. Humans (and chimps) no longer have that great mobility, although some people may move slightly pinna. It has been proven with electrodes these muscles are excited when we perceive a sound that comes from a particular direction (2002).

Auricular muscles responsible of movement of the pinna. Credit

The occipitofrontalis muscle has lost its function to prevent the head from falling, but participates in facial expression.

PALMARIS LONGUS MUSCLE

16% of Caucasians do not have this muscle on the wrist, neither 31% of nigerian people neither 4,6% of chinese people. It can even appear in one arm and not in the other or be double.

It is believed that this muscle actively participated in the arboreal locomotion of our ancestors, but currently has no function, because it does not provide more grip strength. This muscle is longer in completely arboreal primates (like lemurs) and shorter in land primates, like gorillas (reference).

And do you have it or not? Try it: join your thumb and pinky and raise your hand slightly.

mireia querol, mireia querol rovira, palmaris longus, musculo palmar largo, tendon
I have two palmaris longus in the left arm and one on the right. Photo: Mireia Querol

WISDOM TEETH

35% of people do not have wisdom teeth or third molar. In the rest, its appearance is usually painful and removal is necessary.

Yo no tengo el tercer molar. Foto: Mireia Querol Rovira
I don’t have the third molar. Photo: Mireia Querol Rovira

Our hominin ancestors had them, much bigger than ours. A recent research explains that when a tooth develops, emits signals that determine the size of the neighboring teeth. Reducing the mandible dentition and the other along evolution has resulted in reduced molars (and eventually the disappearance of the third).

Comparativa entre la dentición de un chimpancé, Australopithecus afarensis y Homo sapiens. Fuente
Comparison between the dentition of a chimpanzee, Australopithecus afarensis and Homo sapiens. Look at the reduction of the last three molars between afarensis and sapiens, Credit

THE TAILBONE

If you touch your spine till the end, you will reach the coccyx or tailbone. It is three to five fused vertebrae, vestige of the tail of our primate ancestors. In fact, when we were in the womb, in the early stages of embryo development a 10-12 tail vertebrae formation is observed.

Distintos estados en el desarrollo embrionmario humano y comparación con otras especies. Créditos en la imagen
Different stages in human embryonic development (1 to 8) and comparison with other species. Credits in the image.

Subsequently it is reabsorbed, but not in all cases: it has been reported 40 newborns with a tail.

Neonato nacido con cola. Una mutación ha evitado la inhibición del crecimiento de la cola durante la gestación. Fuente
Infant born with tail. A mutation has prevented the growth inhibition of the tail during pregnancy. Credit

Although we have no tail, currently these bones serve as anchors of some pelvic muscles.

mireia querol, mireia querol rovira, coxis, sacro, sacrum, tailbone, rabadilla
Tailbone position. Photo: Mireia Querol Rovira

SUPERNUMERARY NIPPLES (POLYTHELIA)

It is estimated that up to 5% of the world population has more than two nipples. These “extra” nipples can be presented in different ways so sometimes are confused with freckles or moles. They are located in the mammillary line (from the axilla to the groin), exactly in the same position as other mammals with more than two breasts (observe your house dog, for example). Usually the number of breasts corresponds to the average of offspring that has a mammal, so extra nipples would be a vestige from when our ancestors had more offspring per birth. Usual is 3 nipples, but has been documented a case of up to 8 nipples in a person.

Pezón suplementario debajo del principal. Fuente
Additional nipple below the main one. Credit

FIND YOUR VESTIGIAL REFLEXES AND BEHAVIOURS

PALMAR AND FOOT SOLE GRASP REFLEX

Surely you’ve experienced that if you bring anything into the hands of a baby, automatically he grabs it with such a force that would be able to hold his own weight. This reflex disappears at 3-4 months of age and is a remnant of our arboreal past and the way to grab the hair of the mother, as with the other current primates. Watch the next video in 1934 on a study of twins (minute 0:34):

On the feet there is also a reflex of trying to grab something when the foot of a baby is touched. It disappears at 9 months of age.

By the way, have you noticed how easily children climb on any handrails or higher zones in a playground?

GOOSEBUMPS

Cold, stress or intense emotion (eg, listening to some music) causes the piloerector muscle to raise the hair giving the skin the appearance of a plucked chicken. It is an involuntary reflex in which some hormones, like adrenaline (which is released in the mentioned situations) are involved. What utility had this to our ancestors and has in modern mammals?

  • Increasing the space between the skin and the external surface, so that hot air trapped between hair helps on maintaining temperature.
  • Looking bigger to scare off potential predators or competitors.

Chimpancé con el pelo erizado durante un display antes de un conflicto. Foto: Chimpanzee Sanctuary Northwest
Chimpanzee with hair bristling in a display before a conflict. Photo: Chimpanzee Sanctuary Northwest

Obviously we have lost hair in most parts of the body, so although we retain the reflex, it has no use to us or to keep warm or to ward off predators. The hair has been preserved abundantly in areas where protection is necessary or due to sexual selection (head, eyebrows, eyelashes, beard, pubis…), but in general, can also be considered a vestigial structure.

There are more vestigial structures but in this post we have focused on the most observable. In future posts we will discuss other internal structures, like the famous appendix or vomeronasal organ.

REFERENCES

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.

Polilla de Darwin (Xantophan morganii praedicta). Foto de Minden Pictures/Superstock
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.

Anoura fistulata, murcielago, bat
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.

Guepardo persiguiendo una gacela. Foto de Federico Veronesi
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.

Nutria marina (Enhydra lutris) comiendo erizos. Foto de Vancouver Aquarium
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

MIREIA QUEROL ALL YOU NEED IS BIOLOGY

Carnivorous plants

The carnivorism is a nutrition style associated to animals, to the world of heterotrophs. But it has been seen that there are plants that are also able to feed on other organisms. They are called carnivorous plants and their strategies to capture dams are very different and curious.

WHAT IS A CARNIVOROUS PLANT?

A carnivorous plants , even being autotroph, get part of their nutritional supplement by feeding on animals, especially insects.

There are three basic requirements that  carnivorous plants must comply:

  • they must be able to attract, capture and kill the preys. To get their attention, they usually show reddish coloration and secrete nectar. Morphological and anatomical adaptations for retaining and killing the preys such as traps are used.
  • Digestion and absorbance of the nutrients releasedby the damn .
  • And finally, it has to draw significant benefit from the process.

Dionaea muscipula
Venus flytrap (Dionaea muscipula) (Author: Jason).

WHERE DO THEY LIVE?

Carnivorous plants are  not competitive in normal environments and tend to have a small root system, they need this specialization to allow them to grow faster. They are usually found in low mineralization soils, but with a high concentration of organic matter, sunny areas (as they still perform photosynthesis) and with  a high humidity.

Normally they are also calcifuges, i.e., they are not well adapted to alkaline soils and prefer acidic environments, where the source of calcium comes from the prey. They tend to inhabit soils with low oxygen and  saturated in water in a reducing environment. Some are aquatic and live either floating or submerged, but always near the surface.

TRAPS AND EXAMPLES

The capture system is quite diverse, but can be classified according to whether there is movement or not. We consider active strategies for those plants having mechanical or suction movements. Semi-active strategies which present mucilaginous glands and have movement and finally, passive ones, with no motion for prey capture. They can present mucilaginous glands or pitfall traps. Somes amples are given below.

ACTIVE TRAPS

Venus flytrap

In the case of this plant, the traps are mechanical and they are formed by two valves joined by a central axis. These valves are the result of non photosynthetic leave transformations. The stem acts as a petiole and performs photosynthesis, for this reason, it is thickened, increasing its surface and facilitating the process. Furthermore, the valves have nectar glands to attract preys and its perimeter is surrounded by teeth which help the capture, as when the trap is closed, the teeth overlay perfectly avoiding the animal’s escape..

But, what mechanism drives the closing? There’s a gigh number of triggers hairs inside the valves. When the dam is located on the trap and makes the trigger hairs move twice or more in less than 20 seconds, the valves close immediately.

In this vídeos From the BBC one (Youtube Channel: BBC) we can observe the whole process.

Utricularia, the bladderwort

This plant lives submerged near the surface and is known as the bladderwort, because it has bladder-like traps. The bladders are characterized for having sensitive hairs that activate the suction mechanism of the dam. Then, the bladder generates a very strong internal pressure that sucks water in, dragging the animal to the trap. It’s volume can increase up to 40% when water enters.

In the following video we can see the bladderwort trapping a tadpole of cane toad (Youtube Channel: Philip Stoddard):

SEMIACTIVE TRAPS

When I caught you, you won’t be able to escape

The presence of stalked mucilaginous glands is not unique in the carnivorous plant world, many plants use them as a defence or to prevent water loss. But, some carnivorous plants they are used to capture animals, as the sundews (Drosera) does.

The glands presents on the leaves of the sundews are formed by a stalk and an apical cell that releases mucilage. This substance attracts preys by its smell and taste. When the dam is located on the leaves, some drops of mucilage join each other to form a viscous mass that will cover all the prey, preventing its escape. We note that the glands have some mobility and move themselves to get in contact with the prey. Also, as a result, the leaf wrappes, facilitating the subsequent digestion.

The following video shows the operation of this mechanism (Youtube Channel: TheShopofHorrors):

PASSIVE TRAPS

Don’t get to sticky! 

The Drosophyllum‘s case is very similar to the previous one, but this time the stalked mucilaginous glands don’t have mobility and, therefore, the leaf doesn’t have either. The insect gets caught just because it is hooked on it’s sticky trap and cannot escape.

Drosophyllum
Insects trapped by Drosophyllum‘s stalked mucilaginous glands  (Author: incidencematrix).

Carefull not to fall!

Finally, we see the passive pitfall traps. They sometimes have a lid that protects them from an excess wàter getting in, even though it isn’t a part of the trap mechanism. The pitfall traps can be formed by the leaf itself or by an additional structure that is originated from an extension of the midrib (the tendril). The tendril lowers to ground level and then forms the trap.

Nepenthes
Nepenthes (Author: Nico Nelson).

Dams are attracted to these traps due to nectar glands located inside. Once inside, going out is very complicated!  Walls may be viscous,  have downwardly inclined hairs that hinder to escape or present translucent spots that suggest the prey that there’s an exit, acting like windows , confusing and exhausting the prey, making it fall to the bottom, where it will drown. Other species also release substances that stun the preys, preventing them from running away.

Heliamphora
Heliamphora (Author: Brian Gratwicke).

In some cases, large animals have fallen into these traps, though it is considered more as an effect of “bad-luck” than the plants supposed diet, though some traps measure up to 20cm long.

Difusió-anglès

REFERENCES