Ferocious jaws of a lacewing larva protrude from its cloak of debris.
Even in winter on a warm day, lacewing larvae can be found searching for prey on the trunks of trees. Photo credit Cathy Keifer
Last week a loyal viewer of Bug of the Week sent an interesting image of green, lichen covered insects on the bark of a tree. She noted that these insects were romping about just a few days before Christmas. While many insects like praying mantises and eastern tent caterpillars pass the barren winter months as eggs, some insects endure winter as larvae and may be active on the warmish autumn and winter days that have become much more common in our warming world. The mystery of these strange and cryptic insects harkens back to a fable from the sixth century B.C. Æsop wrote the tale of 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.
Like our inquisitive viewer, I am frequently delighted to witness the entomological equivalent of the wolf in sheep's clothing, debris-toting lacewing larvae. These masters of disguise appear as animated balls of fuzz taking a herky-jerky stroll across a blossom, leaf, or bark of a tree. Upon closer inspection, small legs underlie the animated debris and a set of wicked jaws protrude from the front end. Like their relatives naked 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?
Carcasses of past victims and other pieces of organic debris make the perfect disguise for this hunter of tender young things. Watch it hunker down when a bee alights on the blossom.
With the return of spring and warm weather lacewing adults will be found at porch lights and seeking tasty meals on plants.
A fascinating study by the famed biologist Thomas Eisner shed light on the unusual behavior. In a previous episode, we learned the tale of 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 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. On a warmish winter afternoon or 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.
Reference
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. We thank Cathy Keifer for providing the inspiration and an image of lacewing larvae for this episode.