Things have been keeping me away from updating the blog, but I finally found a moment to write about one cool animal that usually shows up at this time of year in Massachusetts – the scorpionfly (Panorpa). Or at least that was the original plan. Since I had, literally, only one, rather lousy shot of this animal, I decided to visit a certain patch of vegetation where I used to see them quite frequently, and photograph some.
Scorpionflies (Mecoptera) are an oddball order of insects, one of the smaller ones, with only about 550 known species (one lineage of Mecoptera has already been featured on this blog.) They are unassuming in their appearance, but what they lack in looks they amply make up for in amazing behaviors and an impressive evolutionary history. Their common name comes from the peculiar morphology of the male’s abdomen in the genus Panorpa, which displays an uncanny resemblance to a scorpion’s “tail” (telson). The difference lies in what sits at the tip of the “tail”– in scorpions it ends with a deadly stinger, in scorpionflies it carries a pair of oversized genitalia.
Last Sunday I drove to Estabrook Woods and started searching for scorpionflies. But I wasn’t having any luck – there were none and clouds of mosquitos were making me miserable. And those annoying crane flies (Tipulidae) were everywhere, flying all over as if they owned the place. In their flight pattern they were confusingly similar to scorpionflies. Suspiciously too similar.
One landed near me, and only then did I realized that those were not crane flies at all, they were indeed scorpionflies! But they were not Panorpa, the common kind. They were hanging scorpionflies (Bittacus), which up to that point I had only seen in China and Mozambique, and it did not occur to me that they might be also present in my neck of the woods.
Hanging scorpionflies do look very much like crane flies, but one major giveaway is the presence of two pairs of wings, as opposed to only one pair present in the Tipulidae and other true flies. The origin of their common name becomes immediately obvious once you see them in their hunting position – they suspend themselves from vegetation by their front legs, keeping the second and third pairs outstretched, ready to snag any insect that flies close enough. Their feet have strong muscles and the scorpionflies are able to use them in a grasping fashion, somewhat similar to the way we use our hands, by closing the fifth tarsomere against the fourth one. The downside of having such grasping hands is the scorpionflies’ inability to walk on horizontal surfaces, and thus they display only two modes of behavior – flying and hanging.
Species of Bittacus feed on all kinds of flying insects and are capable of overpowering seemingly stronger, more muscular ones, such as noctuid and geometrid moths. The prey is killed and devoured with their elongate, scissor-like mandibles that form an elongated rostrum. During the mating season males of some species use their freshly captured prey as a nuptial gift, offered to the female during courtship, and the larger the prey they can offer the longer and more successful the mating. But not all males play fair. A small proportion of so called “transvestite” males approach those males who already hold a prey item, and wiggle the abdomen seductively in a way a receptive female would. Often they are able to convince the honest suitor to hand over the nuptial gift, leaving the sucker confused and ashamed of himself. Other, lazier males, don’t bother with such a nuanced approach, and simply wrestle the food away from courting males, or steal it from mating pairs.