Arxiu d'etiquetes: batesian mimicry

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)

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

References

Anuncis

Animal mimicry: now you see me…

What do you see in the picture above? Maybe snakes… or maybe not? All animals try to enhance their survival rates, and one of the most effective ways to achieve this goal is by looking similar to some environmental elements, either by camouflaging or by imitating traits from other organisms. Mimicry is a complex and surprisingly phenomenon present in almost every animal taxa acting as an evolutionary driving force. Do you know what types of mimicry exist and which animals do perform each one? Are you ready to read more about this topic? If that’s the case, keep reading!

Mimicry vs camouflage (or crypsis)

The word mimicry (that derives from the Greek term mimetikos = “imitation”) was firstly being used to describe people who have the ability to imitate. From 1851 on, its use extended to other life forms.

Sometimes, the term mimicry is used as a synonym of “camouflage or crypsis”. Although these two words are sometimes confused and used equally, from a biological point of view they are well differentiated terms:

  • Mimicry: the ability an organism develops to imitate one or more traits from another organism (with which it’s unrelated) so that it can obtain some benefit.
  • Camouflage (or crypsis, from the Greek word kryptos = “hidden”): the ability an organism has to be unnoticed by its predators (or prays) by copying some environmental traits or by developing a disruptive coloration that allows it to hide.

Some authors consider that camouflage includes only to the ability an animal has for imitating morphological traits from some environmental elements, such as different natural surfaces, plants or even sessile animals (i.e. immobile animals) like corals and sponges (as you can see on the picture below). On the other hand, mimetic animals go further and try to imitate not only morphological traits, but physiological and behavioral, looking for a response from other animals.

Can you see the camouflaged seahorse? (Picture by Stephen Childs, CC).

To sum up: the main objective of mimetic animals is to trick the senses (e.g. sight, hearing, smell…) of the other organisms they live with, in order to induce them a specific behavior that gives mimetic animals a benefit in return.

Types of mimicry

There are different ways to classify the different types of mimicry, but I will show you two main groups of mimicry, in which we will see different subtypes: defensive mimicry and non-defensive mimicry.

Defensive mimicry

The defensive mimicry is specially performed by animals that have lots of predators, so their survival rates depend on avoiding their predators.

BATESIAN MIMICRY

Venomous and poisonous animals tend to develop flashy traits (especially flashy morphological traits, like coloration and menacing sounds) which alert other animals about their danger. This phenomenon is known as aposematism (when an animal has a flashy coloration we talk about aposematic coloration). In the Batesian mimicry, the mimetic organism (that is usually harmless and edible) copies the flashy traits of a venomous or poisonous organism present in its habitat in order to make predators think it’s a harmful species. Thus, the mimetic organism avoids being caught and eaten by predators.

Poisonous Coral Snake (on the left) and non-poisonous Scarlet King Snake or False Coral Snake (on the right). The second one imitates the aposematic coloration of the first one (Source: oakdome.com).

 

MÜLLERIAN MIMICRY

Sometimes, there are various poisonous or venomous species coexisting at the same time in the same habitat that are all being very hunted by predators (and sometimes by the same predator). In some of these cases, even when only one of these species has an aposematic trait to dispel predators, the rest of them try to mimic it and develop this trait (or traits). In contrast with de Batesian mimicry, in this model all species are harmful at some degree.

Try to think that all these species finally develop the same aposematic coloration: when predators prey on one of these species and are harmed in result, probably they won’t attack again any species that has the same coloration pattern. Thus, predation pressure will be distributed within the species matrix.

Different geographical forms of both Heliconius erato (top row) and Heliconius melpomene (bottom row). Heliconius melpomene is a widespread neotropical species well known for its geographic diversity in color pattern. Throughout its range, H. melpomene is co-mimetic with Heliconius erato (which is generally less abundant than H. erato). Both have a disgusting flavor when being eaten (source: heliconius.org).

 

MERTENSIAN MIMICRY

This is an unusual type of mimicry (only a few cases in snakes are known), and it occurs when a harmful species copies an aposematic trait (e.g. coloration) of a less dangerous organism. What could this mechanism be useful for?

Mimetisme_angIn the picture above, we can see that predators that feed on a harmful organism die (e.g. because it’s poisonous), so that the information “this animal is poisonous and mortal, don’t eat it!” won’t be transmitted to the rest of the predator population nor the next generations of predators. Thus, this harmful prey will remain preyed by predators. On the other hand, predators that feed on a less harmful prey and stay alive will have the chance to transmit this information to the rest of the population, so that predators will stop feeding on this prey.

In light of this situation, what do the most harmful organisms do? they try to imitate the aposematic traits of less harmful organisms (like coloration or shape) so that predators that feed on these less harmful organisms and stay alive, learn that all organisms with the same traits are dangerous. So, the predation pressure will fall for all preys.

Non-defensive mimicry

One of the most important types of mimicry within the non-defensive mimicry is the Peckhammian mimicry.

AGRESSIVE OR PECKHAMIAN MIMICRY

Unlike defensive mimicry, in this case are predators (or parasites) the ones that develop the traits of a more or less harmless species (or even of a beneficial one) in order to be unnoticed by their preys or hostages.

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Plagiotremus rhinorhynchos (on the right) is an aggressive mimetic species that imitates another fish known as Laborides dimidiatus or bluestreak cleaner wrasse. Plagiotremus rhinorhynchos (family Blenniidae) imitates youth specimens of Labroides dimidiatus (family Labridae) both morphologically and behaviorally. Many species of fishes enter corals in order to be cleaned from parasites by Labroides dimidiatus. Taking advantage of this situation, P. rhinorhynchos get close to these coral fishes by mimicking the bluestreak cleaner wrasse in order to feed on their tissues (Pictures: the left one by Karelj, CC  and the right one by JennyHuang, CC).

Aggressive mimicry can be confused with some camouflage or crypsis mechanisms, as sometimes these two terms can be overlapped or maybe show no evident differences. This is the case of some abyssal fish species which have one or more filaments of their dorsal fins transformed into lures (sometimes these lures are bioluminescent). These lures sometimes mimic the shape of the abyssal fish’s preys, so those preys feel strongly attracted by them. Some authors propose that preys could be the model organisms and that abyssal fishes would modified their dorsal fin through an evolutionary process.

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Abyssal fish on a photogram from the film ‘Finding Nemo’ (© Pixar, 2003).
abyss-angler2
Abyssal fish…a way more real than the one showed above (with its luminescent lure) (Image source: http://www.bogleech.com/nature/).

A curious case: the automimicry

The automimicry (also known as intraspecific mimicry) is a special case of mimicry that takes place when an organism transforms some part of its body in order to seems like another part of its own body or even of the body of another member of its species (e.g. a male that mimics a trait from females). The objectives of this type of mimicry are to obtain some benefit from other organisms or maybe to be unnoticed by their predators or preys.

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The northern pygmy owl (Glaucidium californicum) has two big dark spots behind its head which remind of two big eyes (picture by Michael Durham).

Mimicry makes animals to evolve!

Mimicry is one of the processes that makes animals to evolve faster (do you want to learn more about evolutionary processes? Enter this link!).

These changes may occur in a higher or lower speed. So, what about those animals that mimic other organisms? Mimetic animals are in constant selective pressure to look more like their models in order to go unnoticed and improve their survival, but at the same time imitated organisms (the models) are also under selection to sharp their ability to discern between models and imitators.

.            .             .

Thus, mimicry is an incredible evolutionary engine: a perpetual struggle between mimetic organisms and imitated ones in order to improve their respective survivals.

REFERENCES

  • Bone Q., More R. Biology of fishes. 3a ed. Taylor & Francis.
  • Campbell, N.A., Reece J. B. 2007. Biología. Ed. Médica Panamericana.
  • Cheneya K.L., N. Justin M. 2009. Mimicry in coral reef fish: how accurate is this deception in terms of color and luminance?. Behavoural ecology, Oxford Journals. Vol 20. P. 459-468.
  • Harper D. Online Etymology Dictionary.
  • Kashyap H. V. 2001. Advanced Topics In Zoology. Ed. Orient Blackswan.
  • Sarmiento O.F., Vera F., Juncosa E. J. 2000. Diccionario de ecología: paisajes, conservación y desarrollo sustentable para Latinoamérica. Ed. Abya Yala.

Main picture source: www.yedirenkhaber.com.

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