Thursday, November 12, 2020

Junk Bugs


At the end of the WOLF School field trip, Courtney Reece (WOLF Teacher) pointed to a tree trunk and said, "Look at the little trash bugs."  There were 10 of these 5-6 mm white clusters scattered around the bark among the green moss and lichen patches.  They were stationary but when picked off into a bug box they started to put on a slow show.  You can see one in action in this video by Ben Caruthers.

Click to enlarge

Trash bugs (aka junk bugs) are also called aphid lions for their favorite food that they stalk like any other carnivore.  These are the larvae of green lacewings that we had discussed in a past blog but these were smaller and completely covered with bits of lichen.  Even when I flipped one on its back it was hard to believe it was a live insect without using a magnifier.  

You can just make out the legs and fangs by enlarging the photograph above.  They are easier to see in this recent find sitting on my fingerprint.  These are serious and can put the hurt on their tiny prey.

Naked green lacewing larva with aphids

 Green lacewings are members of the Chrysopidae family.   Many species have "naked" larvae, fearsome appearing predators with exposed curved hollow mandibles which inject digestive juices into prey before sucking out an aphid slurppy.  They look like a tiny alligator that is bulging in the middle from swallowing a pig whole.

"Naked forms do not construct a packet and tend to rely on swiftness and ambushing when hunting. On the contrary, debris-carrying forms use stealth and crypsis to capture their prey. Debris-carrying chrysopid larvae can be selective towards the collection of one or more materials for the construction of the debris packet. These materials may include victim's waxy flocculence, arthropod exoskeletons, fragments of dried leaves, wood, lichens, mosses, trichomes, snail shells, silk, particles of sand or soil, frass (excrement of herbivorous insects), or the larvae’s own exuviae."

Blue=legs, red = jaws

The "decorated larvae" like Courtney's are rounder with long bristles with knobs on the end sticking out the sides.  They collect debris such as lichen as well as the bodies of their aphid victims, a morbid display of recent meals.  

Many ants farm aphids for their honeydew and will attack their predators.  Studies have shown that a decorated larva can sneak by the guarding ants to collect a tasty meal and a few more trophies.

So what is with the debris piled on it back?  Is it simply messy grooming of a larva with a bad haircut? Maybe a macabre example of a psychopathic killer keeping trophies of it victims. Actually it is an important part of its hunting strategy, as described in Bug of the Week.

 "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. "

Lacewing on my arm

Many adult lacewing species are vegetarians, feeding on pollen, nectar and honeydew with the help of symbiotic yeast in their guts to break down these nutrients.  Some are more generalists, spicing up their diet with the odd aphid or other arthropod.

Lacewing eggs - Tom Murray

Another "fun fact" (note to self; spending too much time with the 5th grade WOLF Class.)  They produce eggs that are suspended individually from tiny threads, usually on the under side of leaves in the vicinity of an aphid colony.  These are very small but a rewarding find for a naturalist with curiosity and a camera.

You can watch our little junk bug walk upside down clinging to the lid of a bug box as well as do back flips in this video.