Predatory Wasps

Ambush wasp (left), Cicada killer wasp (right)

Yellowjacket (left), Bald-faced hornet (right)

Predatory wasps may be social (many individuals living in a nest with a queen), solitary (each female produces and rears her own young), and some are frightening enough to strike terror into our hearts, but these fearsome predators work diligently to control garden pests.  Although all social wasps will defend their nest with a painful sting if disturbed, with a little bit of care on our part (do NOT disturb the nest!) we can avoid raising their ire while benefitting from their appetite for other insects. Solitary wasps, on the other hand, are non-aggressive and do not sting in defense, but only to capture prey; you’d have to handle or sit on one to get stung. As effective predators of many insect pests, wasps are considered beneficial, but a social wasp nest in the wrong place may need to be removed.  

Important species in Maryland: Social wasps such as yellowjackets (sometimes incorrectly referred to as “ground bees” from the habit some species have of nesting underground), paper wasps, bald-faced hornet (actually a type of native yellowjacket), and European hornet. Solitary wasps include cicada killer wasps, potter wasps, digger and sand wasps, and mud daubers.   

Social wasps make a new paper nest each year in which they produce large colonies of offspring. Most feed their young a diet of living insects, chewed first by adult workers before being fed to larvae. Some nests are very large, generally spherical in shape, fully covered with a papery material, and typically hang from tree branches (baldfaced hornets, aerial yellowjackets). Other nests may be open-celled (lack a papery covering) umbrella-shaped combs, and usually hang from eaves or ceilings of open-air structures (paper wasps). Still others may build their paper nests in hollow trees, holes in the ground, or other cavities such as wall voids or hollow trees (European hornet). Social wasps capture their prey with their jaws; their sting is used for defense of the nest.

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.

NOTE: 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.

Life stage(s) that feed on pests: Adults, which also provide pests as food for larvae. Some adults also visit flowers for nectar or aphid colonies for honeydew (yellowjackets, hornets, potter wasps).

Pest(s) fed on: A wide variety of insects and spiders, including caterpillars, beetles, beetle larvae, flies, true bugs, other wasps, and a variety of other larger insects.

Appearance:
Nests: Paper-making social wasp nests range from open-cell umbrella-shaped hanging nests, to large ovoid structures completely covered with a papery material. Potter wasps construct beautiful, small marble-sized pots of mud. Mud daubers construct slim, “pipe organ” tubes of mud up to several inches long. Many nests are underground and never seen.
Larvae: Whitish grubs; rarely seen because they develop within well-protected nests.
Adults: Many social wasps range in length from 1/2 to nearly 1”; are banded in black and yellow, but sometimes cream. The European hornet is up to 1” long and much stouter than yellowjackets; yellow with black markings on the abdomen, red and black marked thorax, and a red head. Potter wasps are a little smaller and chunkier in appearance; generally black with yellow or cream bands. Mud daubers are 1/2 to 1 1/2” long; blue-black in color; and long-bodied with a very thin waist. Unlike bees, wasps are not hairy, or fuzzy. Cicada killers are very large (up to 2”), black and yellow banded solitary wasps with reddish wings that feed exclusively on cicadas. The entrance to their burrows may be mistaken for those of small rodents.

Where to find: Generally throughout the garden and landscape feeding on pests. Some nests are readily seen. European Hornet workers are active day and night and may be attracted to lights at night.

How to attract and conserve: Grow flowering plants that produce the nectar and pollen eaten by adult wasps. Avoid or reduce use of broad-spectrum pesticides.

Contributors: Mike Raupp, Jon Traunfeld, and Chris Sargent 
We would like to thank Dr. Nancy Breisch, UMD Entomology, for her contributions to this page.

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