Solitary wasps – natural pest controllers

By Sara Scudier

OSU Ext. master gardener volunteer

When we think of beneficial insects that inhabit the garden, wasps are not very likely to come to mind for most home gardeners. In fact, they’re not likely to make any lists.

Adult solitary wasps may feed on nectar and pollen, or they may be carnivores and feed on a wide variety of insects and spiders, including caterpillars, beetles, beetle larvae, flies, true bugs, other wasps and other larger insects.

Solitary wasps, also called hunting wasps, may nest in holes in the ground (digger and sand wasps), construct nests of clay or mud (potter wasps, mud daubers) above ground, nest in small voids they line with mud, or excavate chambers in the pith of plants.

Many individuals may nest in a common area, creating the appearance of a large community, but each wasp constructs her own nests and each nest contains chambers with only a single larva.

Some solitary wasps provision their nests with a wide variety of living arthropods for their developing young, while others specialize in the type of prey they capture.

Solitary wasps are not aggressive and do not sting in defense. They sting only to capture prey; you’d have to handle one or sit on one to get stung.

As effective predators of many insect pests, wasps are considered beneficial.

It is important to know if you have social or solitary wasps before considering control for nuisance reasons.

A stream of wasps entering and exiting from a single hole in the ground indicates social wasps that may defensively sting if the nest is disturbed.

If you have a few to hundreds of holes in an area with only one or two wasps around each opening, you have harmless solitary wasps and can safely play croquet among them.

Other solitary wasps are so small that they are invisible to the naked eye. They are harmless to humans and a natural enemy of pest insects.

Parasitic wasps lay their eggs on unsuspecting garden pests. These parasitic wasps are important for pest control, and are also necessary as pollinators in agriculture and home gardens.

While you may not see parasitic wasps, you are likely to have seen the fluffy white egg cocoons on the backs of tobacco hornworms. These indicate that a wasp has parasitized it. Hornworms with these white cocoons should be preserved on the plant, or moved to another area so that the wasps can finish maturing and continue to be beneficial in garden.

Solitary wasps are a harmless and very beneficial addition to the garden. This summer, watch your garden for these valuable visitors.

To learn more about wasps, visit go.osu.edu/beesandwasps.