Friday, September 16, 2016

A Beetle Mimicry Complex

This week, on one of my daily walks around our Colorado Springs neighborhood, I encountered a beetle on the sidewalk that gave me reason to pause. I initially dismissed it as a species of soldier beetle that is extremely abundant at this time of year, but something looked a little "off." Sure enough, it was something else; and that got me thinking about mimicry among all these beetles.

Blister beetle, Epicauta stuarti

The beetle on the sidewalk turned out to be a blister beetle, Epicauta stuarti, a species I had not seen before. Blister beetles, family Meloidae, are well known for containing high concentrations of the potent, irritating chemical cantharidin. Blister beetles exude the chemical in liquid form from leg joints and from between other body segments if the insect is squeezed or crushed. The chemical goo can raise painful, scarring blisters on sensitive skin; it can be fatal if ingested.

Ironically, many, if not most, blister beetles don't advertise their toxicity with bright "warning colors." Epicauta stuarti is one that does, but the interesting part is that its pattern of black and orange is very similar to that of our two common autumn soldier beetles. Soldier beetles are in the family Cantharidae, and they also have chemical defenses, which they secrete from abdominal glands. The Colorado Soldier Beetle, Chauliognathus basalis, is common on the plains. Its close relative, C. deceptus, replaces it in the foothills and mountains.

Colorado Soldier Beetle

This kind of shared color pattern that reinforces predator deterrence is called Müllerian mimicry. Both animals can back up their colorful advertisement of toxicity with actual chemical weaponry. This is a very interesting example of mimicry, but it doesn't end here. Other local beetles have jumped on the bandwagon.

End Band Net-wing Beetle, Calopteron terminale

Also appearing at this time of year is the End Band Net-wing beetle, Calopteron terminale. They generally occur in far fewer numbers than the soldier beetles, but can be mistaken for them with just a passing glance. It is widely assumed that net-winged beetles (family Lycidae) are distasteful to predators, because they have colorful patterns in many cases. Whether this has been proven I do not know.

Net-winged beetles may exaggerate the effect of their wardrobe by raising and lowering their wing covers (elytra) in a unique display. As adults, they feed on nectar, and the "honeydew" secreted by aphids and related insects as a sweet liquid waste product. Larvae of netwing beetles feed on fungi or metabolic products of fungi. Whether this diet can be converted into toxic compounds is debatable.

Longhorned beetle, Crossidius discoideus

While the jury may still be out on whether net-winged beetles are indeed toxic, there is no question that yet another mimic in this complex is pulling one over on predators. The longhorned beetle Crossidius discoideus fools us into thinking it is dangerous to eat by mimicking the pattern of the solider beetles. It can even be found on the same flowers as the soldier beetles and is difficult to easily separate from them, except for its long antennae. This brand of mimicry is called Batesian Mimicry, whereby a harmless animal masquerades as a dangerous one.

Crossidius discoideus has no common English name. As a larva, it bores in the root crowns of Broom Snakeweed, Gutierrezia sarothrae, or Jimmyweed (Isocoma spp.). The adults feed on flower pollen and nectar. Broom Snakeweed is also where the blister beetles hang out, so I may have to look more thoroughly for them now.

Longhorned beetle, Batyle suturalis

Yet another kind of longhorned beetle, Batyle suturalis, appears just before the populations of soldier beetles explode. Is it, too, taking advantage of a similar color pattern to gain "cover" from predators? What I would like to know is which of the truly toxic beetles started this whole complex. The blister beetle? The solider beetles? We will likely never know, and that is part of the appeal of entomology. It is an endlessly curious endeavor, seeking the answers to more puzzles than mankind will ever unravel.

Saturday, September 3, 2016

Do Insects Feel Pain? A Revealing Question

At some point in their career, every entomologist will be asked the question "do insects feel pain?" A surprising amount of research has gone into answering that question or, in some instances, unrelated research has provided insight into that query. My answer to that question has more to do with the person asking it, and as far as I know, that is a unique response.

Questioning the capacity for insects to feel pain says more about the one who intends to inflict it.

As one who interacts with the public more than many entomologists, it has become evident that while some people have no qualms about ending the life of an insect, even advocating extremely inhumane techniques ("Kill it with fire!" is a common reply to someone else's social media request to identify a household insect), there is an increasing tolerance for insects, even in the home. If the creature is unwelcome, there is now often a plea for a non-lethal means of dealing with the uninvited arthropod.

The flipside of this more empathetic response to "bugs" is the question of whether insects feel pain. The obvious, hoped-for answer is "no, they don't." The person asking is then relieved of guilt for harming or killing any insect in the past, present, and future. So, while the new trend is for more people, especially women, to seek humane methods of insect control, many people still look for examples of how insects do not deserve empathy and compassion as a way to vindicate their own behavior towards other organisms.

The bottom line in the question of whether insects feel pain is thus the unspoken question of whether killing insects and spiders falls into the category of cruelty to animals. Legally, it would be difficult to argue that insects, being animals, are exempt from that crime. Obviously, this is not the case, and I do not see that implied public consensus changing anytime soon. Swatting a mosquito could be an act of "self-defense," though, considering the atrocious diseases that those biting flies can transmit.

Ok, so you want a scientific answer? Most entomologists I know resort to the short answer that insects do not have "pain receptors" like higher animals. This means they have no nerve cells devoted to the perception of pain. Insects can sense heat and cold, for example, and various chemical and tactile stimuli, but not pain as we would define it.

Is the wasp feeling no pain while being killed by the spider?

The fact that many insects, and other arthropods, willingly sacrifice limbs and other body parts in order to survive predator attacks is a testament to how apparently immune to pain they can be. A missing leg hardly slows down a grasshopper. Tattered wings rarely encumber a butterfly finishing its mission of mating and procreation.

As a colleague and fellow blogger noted in his own treatment of this question, another important aspect of physical pain is the emotional distress that comes with it. Ascribing human emotions to non-human organisms is known in the scientific community as "anthropomorphism," and is considered a big no-no when attempting to conduct unbiased research and observations. So ingrained is the concept of avoiding anthropomorphism that we now have to question whether the unemotional conclusions we draw in animal behavior studies are really the correct ones. The truth probably lies somewhere in the middle.

The fact that people are asking questions like this that leave open the possibility that insects and other arthropods are sentient beings is a hopeful sign, regardless if that belief is based in reality. We could certainly stand a little more empathy for other living things. Then again, look how we treat other members of our own species.

Source: Ballenger, Joe, 2016. "Do insects feel pain?," Ask an Entomologist.