Zorapterans at the VCU Rice Center
By Arthur V. Evans
Smithsonian Institution, Washington, D.C.
Virginia Museum of Natural History, Martinsville, Va.
Virginia Commonwealth University, Richmond, Va.
My stepson Graham Wilson and I drove out to the VCU Rice Center in Charles City County, Va., this morning in search of insects to photograph. By late morning, the temperature was in the high 50s and the only insect seen on the wing was a single mourning cloak. Undaunted, I began searching for snags and logs with loose bark.
With Graham looking on, I slowly peeled back a slab of bark from a large fallen oak. I soon caught a glimpse of several tiny, pale insects less than 1/8 inch (2.0-3.0 mm) long as they scurried about the smooth, moist patch of exposed wood. I immediately recognized the wingless, termite-like animals as angel insects, or zorapterans. They quickly scrambled to find a dark nook or cranny to escape the sudden invasion of light.
Angel insects are not rare and are sometimes quite abundant locally. They simply escape attention because they are small, secretive and easily overlooked. Adults are most active in spring and summer and are typically found in deciduous woodlands. Here in Virginia, I usually find them under the bark of rotten logs, often in association with moist accumulations of termite frass.
The order zoraptera was proposed in 1913 by the Italian entomologist Filippo Silvestri. The name of the order is derived from the Greek words zoros (sheer or pure) and pteron (wings). Of the 32 species of angel insects known worldwide, most are tropical. Only two are found in the U.S.: Hubbard’s angel insect, Zorotypus hubbardi Caudell (eastern U.S.) and Snyder’s angel insect, Z. snyderi Caudell (southern Florida).
Hubbard’s angel insects are gregarious and live in small groups; isolated individuals are incapable of surviving for very long on their own. They are usually found under the bark of rotting logs, where they eat fungus, especially spores and the branching, threadlike fungal structures known as hyphae. Dead nematodes, mites, small insects and other minute arthropods are also scavenged when there is an opportunity. In the laboratory, angel insects thrive on a diet of yeast and crushed rat chow, as well as their own remains.
Angel insects spend much of their time grooming themselves or each other. They reproduce sexually or by parthenogenesis. Before mating, males court females by offering them droplets of fluid secreted by a special gland on their head. Receptive females mate for several days with the same or different partners. Soon they will lay batches of eggs, cover them with chewed bits of food, and watch over them for several weeks until they hatch. The larvae resemble small versions of the adults and molt four or five times before reaching maturity. The larvae are distinguished from the adults by their smaller size and eight-segmented antennae.
Most angel insects are pale, wingless and blind. Their eyeless, triangular heads are equipped with chewing mouthparts. Adults have a pair of antennae with nine bead-like segments. Their hind legs are equipped with bulging thighs armed with a row of small, sharp spines underneath. All six zorapteran feet are two-segmented, the first of which is very short.
Tough times as a result of overcrowding or dwindling food supplies trigger the production of eyed and winged males and females that soon take to the air in search of better living conditions. Their four transparent wings resemble narrow paddles and have few supporting veins. Although similar in shape, the forewings are distinctly longer than the hindwings. Zorapterans are often attracted to lights on warm nights. Like termites, they shed their wings easily upon entering a new log, leaving only four small stubs behind.
Zorapterans have stumped systematic entomologists for years in terms of trying to sort out their relationships with other insects. Unfortunately, their currently sparse fossil record has yet to shed any light on the subject. Originally considered the nearest relative of termites, zorapterans have since been allied with termites plus cockroaches, earwigs, earwigs plus cockroaches plus mantids, thrips or barklice. Currently, they are considered as closely allied with another curious group of insects, the webspinners (embioptera).
Hubbard’s angel insect, zorotypus hubbardi, is one of two species of zorapterans found in the U.S.