The Amazing Ichneumon

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Published on: May. 2, 2002

Last revision: Nov. 12, 2010

On a hot July afternoon, I watched a strange insect forcing its tail into a dead log. I assumed I had discovered an unusual species, but I was later surprised to find it was merely a common variety of insect, the ichneumon wasp.

Ichneumons (pronounced Ick'-new-mons) are a large family among many different types of parasitic wasps around the world. Ichneumons are often incorrectly referred to as flies, but they are directly related to wasps and bees. They are "parasitic" because they lay their eggs on or in another insect species called a "host." The ichneumon's larvae develop and grow at the expense of the host insect. Ultimately, the ichneumon larvae kill the host.

All parasites are not bad. Ichneumon wasps are economically and environmentally important because their larvae feed on and destroy many insects injurious to humans and plants, especially to food crops. Ichneumons are important in the control of clinch bugs, boll weevils, codling moths and asparagus beetles, just to name a few. The value of parasitic ichneumon wasps in the control of agricultural pests is incalculable. They are extremely helpful to the environmental in general, and farmers in particular.

Larval ichneumon species that feed on hosts in open habitat usually develop as internal parasites. Those that feed on hosts in concealed places usually develop as external parasites. Generally, a single larva hatches from one host, but sometimes many larvae can develop from a single host. A tomato hornworm with many small white objects attached to its body is an example of a host with multiple larvae. These white objects are actually cocoons of the larvae hatched from eggs laid by a different insect.

Scientists estimate there may be from 40,000 to 100,000 species of ichneumon wasps worldwide. They vary greatly in color and size, but they all have long, light-colored antennae with many sections, two recurrent veins in each wing, a dark spot on each wing, and a slender, curved abdomen. Ichneumon wasps range from 1/8-inch to 5 inches long. Most are brown or black with yellow, white or red markings. Females have an egg laying organ called an ovipositor at the end of their body.

The megarhyssa species I observed and photographed forcing its tail into a log was about 1 3/4 inches long with yellow, "V" shaped markings on its black body. The outstanding characteristic of this particular species is the trailing, thread-like ovipositor of the

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