Beneficial Wasps 

Elaine Feinberg 
Frederick County Master Gardener Program

I am allergic to the sting of a wasp so I am constantly destroying wasp nests on my porch and under the eaves of my house. Because I live in an old farm house, there are many openings through which they can enter my house. Many times I find them stuck to my clothing and a few times I have unwittingly put on a shirt and have received a sting. It was therefore so exciting to find a wasp that not only is beneficial but does not sting humans, even when provoked. Their sting is meant for paralyzing their prey.

The Cicada Killer Wasp is one of North America's largest wasps. It is more than one inch in length - and belongs to a group called digger wasps. They have a mostly black glossy body with pale yellow markings on the abdomen; they resemble large Yellow Jackets. Their large eyes are used to seek out victims. They are most active in mid-summer when cicadas are numerous because they alone are their prey. Around the middle of July the female wasp digs her burrow in dry clay soil. She digs a tunnel and excavates a few caverns at the bottom, big enough to store two cicadas. She stings the cicada on its underside and hits a vital nerve. The cicada does not die but becomes paralyzed and unconscious. She inverts the cicada so that, with its feet up, it won't catch on twigs, stone, and matted grass as she carries it down the tunnel to the circular cavern at the bottom.

She lays a single egg and fastens it to the underside of the cicada. After a few days, the larva hatches from the egg and immediately feeds on the paralyzed insect. After a week or two of continual feeding, the larva becomes an immature wasp. It forms a cocoon of silk and soil and lies dormant through the winter, changing into a pupa in the spring. When it digs itself through the earth to the open air it emerges as a mature wasp.

The female's life is very busy, but the male's only duty is to fertilize the female's eggs. He spends his life in pursuit of pleasure. Only the larva of the cicada killer is carnivorous. The adults feed on nectar and sap. They often cluster at the holes made by sapsuckers. They love fermented sap and have sometimes become inebriated.

With the coming of the first frost, the wasps' tissues freeze and they die - but, beneath the soil, the next generation, sleeping in their cocoons, await the summer to begin the cycle again.

There are other parasitic wasps which are beneficial in the garden and will not or cannot sting humans; in fact, their eggs and larvae are available commercially. One is the Aphid parasite which is the size of an aphid. This wasp is tiny and is black or brown. Much like the Cicada Killer Wasp this wasp inserts her eggs into aphids. When the larvae hatch, they feed on the aphid. Other parasitic wasps parasitize a variety of insects such as caterpillars, beetle larvae, flies and hornworms. They are part of a large group of small to large wasps which are black, yellow or brown with pinched waists and clear wings.

Keep an eye out for the good guys!

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