Arxiu d'etiquetes: venomous arthropods

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

Venomous and poisonous arthropods: what makes them different?

After talking about venomous mammals, fishes and lizards, ‘All you need is Biology’ brings you this post about venomous and poisonous arthropods. We will try to explain you what makes them different and which arthropods produce some kind of toxic substance (and how they do it). It will probably surprise you!

Venomous vs poisonous animals

Although some people normally use these words interchangeably, they really mean the same? The answer is NO.

A venomous animal develops specialized organs or elements (such as fangs, teeth or stings) to actively inoculate venom inside the body of their victim as an offensive or defensive mechanism. On the other hand, a poisonous animal does not develop these type of organs, but specialized tissues or glands that produce toxins that are released passively as a defensive system; others acquire these substances from their diet. Sometimes, the toxin is not produced in any specific organ, but integrated within body tissues as a defense against predation.

Despite these differences, once in the body venoms and toxins can cause similar damage, which depends on their mode of action, the assimilated amount and the victim’s features. In humans, effects caused by these substances range from irritation, inflammation or redness to severe systemic damage in cases of powerful poisons.

Venomous and poisonous arthropods

Arachnids

Arachnids (subphylum Cheliceromorpha) include two of the better known venomous arthropods: spiders and scorpions. Both groups develop specialized organs to inoculate venomous substances which use either to hunt and defend themselves against predators or potential enemies.

  • Spiders

The specialized organs for venom inoculation in spiders are the chelicerae, a pair of preoral appendices typical of Cheliceromorpha which they use to grab the food. Spiders’ chelicerae, which are fang-shaped, are related to basal venom glands. These fangs have an internal duct that finish in a terminal opening through which venom is released and injected inside victims’ bodies like a hypodermic needle.

Spiders have the most evolved form of chelicerae: jackknife chelicerae. The two parts of the chelicerae come together like a folding knife, and when threatening to attack, the spiders rise the chelicerae and open the angle of the fangs.

Spider’s chelicerae. Public domain image (CC0) obtained from pixabay.

Some of the most dangerous spiders for humans are the Australian funnel-web spiders (genera Atrax, Hadronyche and Illawarra). Their venom is toxic to sodium channels, which results in the massive release of neurotransmitters.

“Funnel web spider” of the species Hadronyche cerberea. Have you noticed the drop of venom in its chelicer?. Picture by Alan Couch on Flickr (CC 2.0).
  • Scorpions

The most distal part of the scorpion tail, the telson (an additional segment found in several arthropods), has become a venomous organ that ends in a stinger. Like chelicerae in spiders, telson in scorpions is related to venom glands that contain toxic substances.

Scorpion of the species Centruroides vittatus, common in the middle of EUA and in the north of Mexico. In red, telson ended in a sting. Public domain image (CC0).

Scorpion venom is usually rich in neurotoxins that alter both the central and the peripheral nervous system of the victim by dissociating the parasympathetic and sympathetic nervous systems. In humans, the effects of their sting vary from intense local pain (with minor inflammation) to cardiac arrhythmias and acute pulmonary edema, like in the Indian species Hottentotta tamulus, which is considered one of the most venomous scorpions in the world.

BE CAREFUL! Neither all arachnids nor related groups are venomous; e. g. harvestmen, camel spiders and whip spiders (Amblypygi) ARE NOT venomous.

From left to right: harvestman (Daniel Jolivet on Flickr, CC 2 .0), camel spider (CC 3.0) and whip spider (Geoff Gallice on Flickr).

Myriapoda

The subphylum Myriapoda is divided in two classes: Diplopoda (millipedes) and Chilopoda (centipedes), and both produce toxic substances.

  • Millipedes

Millipedes, which have an elongated body composed of a lot of segments with two pairs of legs (rarely just one pair), are detritivores and inoffensive. However, they release toxins (alkaloids, benzoquinones, phenols) as a defensive mechanism to prevent predation. Some of these released substances are caustic and can burn the exoskeleton of other arthropods or cause skin and mucous inflammation in bigger animals.

Millipede toxins are produced inside repugnatorial or odoriferous glands and then excreted through small micropores located at both sides of the body when being crushed or feeling threatened.

At the first sight, micropores are difficult to see. Picture by Thomas Shahan on Flickr (CC 2.0).

TRIVIA: black lemurs from Madagascar (Eulemur macaco) grab and bite millipedes to stimulate their secretions, and then rub them all over their body. It is thought that lemurs cover themselves on millipede’s toxins since these work as insect repellent.

If you want to learn some more about this behaviour, don’t miss the following video. We recommend you to stay until the end…the final result will probably surprise you!

  • Centipedes

Centipedes also have a segmented body like millipedes; however, each segment has just a pair of legs. While millipedes are detritivores, centipedes are carnivorous arthropods that hunt their preys actively. To do so, they have developed two large forcipules originated from the first pair of legs which can inject venom contained in glands in the trunk of the animal. They also bite when feeling threatened.

Forcipules of Scolopendra cingulata, by Eran Finkle (CC 3.0).

The Scolopendra genus causes the most severe injuries. However, despite causing an intense pain when stinging, almost all envenomations caused by centipedes spontaneously resolve without complications.

Insects

Despite their diversity, there exist just a few cases of venomous/poisonous insects (class Insecta).

  • Beetles

Some beetle families (Coleoptera order), such as Meloidae, Oedemeridae and Staphylinidae (Paederus and Paederidus genera) contain toxins within their hemolymph which are released by compression as a defensive strategy against predators. These substances cause skin burns, redness and inflammation in humans.

Sptaphylinidae of the species Paederus littoralis, from Spain, France and Italy. Picture by Alvesgaspar (CC 4.0).

Meloidae and Oedemeridae hemolymph contain cantharidine, while the one of Paederus and Paederidus contains pederine, a substance that is exclusive of females of these beetles and of certain marine sponges, and which is thought to be produced by symbiont bacteria.

  • Bugs

Although some bugs (suborder Heteroptera) are better known for being disease vectors, they also cause different types of skin injuries in humans due to the release of caustic and inflammatory substances as a defense when being compressed (e. g. Pentatomidae family) or by the injection of salivary enzymes that are normally used to kill and dissolve preys (e. g. Belostomatidae family).

Belostomatidae. Public domain image (CC0).
  • Hymenopterans

Most of wasps, bees and ants (Hymenoptera order) produce toxins as a defensive mechanism. In most of those cases, females develop a stinger at the end of the abdomen resulting from the evolution of the ovipositor (Aculeata infraorder); however, there are also some groups that defend themselves by biting.

Ants (Formicidae family) usually attack by biting, but some species, such as those in the group of the fire ants (Solenopsis spp.) and the bullet ants (Paraponera spp., Dinoponera spp.), also have stingers like bees and wasps. Formic acid probably is the best-known toxin produced by ants, but is unique to the Formicinae subfamily; fire ants, for example, inject piperidine alkaloids. The sting of the bullet ants, which are distributed throughout center and south America, is considered the most painful sting for humans caused by an insect according to the Schmidt Index (which considers it to be as painful as a gunshot!).

Red ant of the species Solenopsis invicta (left, public domain image (CC0)) and bullet ant of the species Paraponera clavata (right, April Nobile / © AntWeb.org / CC BY-SA 3.0).

Females of most of bees and wasps within the Aculeata group develop an abdominal stinger. Their venom is usually rich in phospholipases, producing effects ranging from local inflammation to severe anaphylactic reactions (when suffering of hypersensibility or after being attacked by thousands of insects, as it has happened several times with the killer bee in America). The sting of the tarantula hawk (Pepsis formosa) from Mexico and southern USA, is considered the second most painful after the one of the bullet ant.

Pepsis formosa, a tarantula hawk. Public domain image (CC0).
  • Butterflies and moths

A lot of butterflies and moths (Lepidoptera order) produce toxins either during their larval stages, adulthood or both as a defensive mechanism against predation.

Sometimes, caterpillars are covered by urticant bristles or hairs that cause skin lesions (erucism), as in the case of the pine processionary (Thaumetopoea pityocampa), a harmful plague for pines which is very spread in southern Europe and America.

Pine processionary caterpillar nest, by John H. Ghent (CC 3.0).

On the other hand, adults of some species, like those of the monarch butterfly (Danaus plexippus) and Zygaena spp., both showing flashy colors (aposematism, a type of animal mimicry), develop toxins within their corporal tissues to prevent predation. The monarch butterfly obtains these substances by feeding on toxic plants of the Asclepias genus.

Zygaena transalpina, by gailhampshire (CC 2.0).

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Have you found this information interesting? Do you know any other venomous or poisonous arthropod? Feel free to leave your comments below!

References

The main image is of public domain (CC0) and was downloaded from Pixabay.