In the sixth century B.C., Æsop wrote a fable about a clever wolf and a vigilant shepherd. The wolf had no luck catching sheep under the watchful eye of the shepherd. However, the crafty wolf donned a sheepskin, snuck past the shepherd into the flock, and enjoyed a tasty mutton meal. Last summer, I was delighted to witness the entomological equivalent of the wolf in sheep's clothing, a debris-toting lacewing larva.
Carcasses of past victims and other pieces of organic debris make the perfect disguise for this hunter of aphids.
I first noticed this master of disguise as an animated ball of fuzz taking a herky-jerky stroll across a blossom in my flower garden. Upon closer inspection, I could see small legs on the animated debris and a set of wicked jaws protruding from the front end. Like their relatives the green lacewings, these larvae are ferocious predators of many soft bodied insects including aphids and scale insects. As one of the true psychopaths of the insect realm, this predator takes the spent carcasses of its victims and places them on its back amidst the collection of other organic debris, including lichens and small pieces of vegetation. To what purpose is this? Is it some kind of macabre trophy collection of a deranged invertebrate killer?
A fascinating study by the famed biologist Thomas Eisner shed light on this unusual behavior. In a previous episode, we learned the tale about ants as guardians of aphids. Aphids provide ants with honeydew, a carbohydrate rich food, and ants protect aphids from insects that would like to eat them, such as lacewing larvae. By removing the debris from the backs of the trash collecting lacewing larvae, Eisner discovered that lacewings attempting to enter an aphid colony for dinner were immediately detected by the shepherds, the ants, and tossed out of the colony and sometimes off the tree. However, when the lacewing larvae disguised themselves in aphid debris, products made by the aphids such as wax or skins, they easily snuck past the ants and enjoyed an aphid feast much the same way Æsop's wolf snuck past the shepherd for a tasty lamb dinner.
When spring finally arrives and blossoms return, look for small tufts of wandering fuzz or roving lichens on flowers and the bark of trees and you may behold these tiny aphid wolves in sheep's clothing.
Information for this bug of the week came from the wonderful reference “The love of insects” by Thomas Eisner. This great book contains many fascinating stories about bugs and their strange little lives.