Yellowjacket Biology
Yellowjacket Biology

Wasp is a general term, and includes yellowjackets as well as other stinging and non-stinging Hymenoptera . Most wasps are parasites (or parasitoids) of other insects and do not sting. These wasps, often very tiny, will lay their eggs and develop inside other insects, eating and killing them. The term 'yellowjacket' originated in North America- in british english 'wasp' is used. Hornet is used in several ways- referring to large social wasps (Genus Vespa) including the European Hornet- introduced and established in eastern North America and also to Aerial (or exposed) nesting yellowjackets.

Some generalizations:
Yellowjackets are beneficial as they mainly feed on other insects, especially flies.

Yellowjacket colonies last only one season- they do not overwinter (one species introduced from Europe will sometimes overwinter in areas with mild winters). The yearly cycle is: new queens overwinter, start new nests by themselves in spring or early summer, lay eggs which produce worker yellowjackets which take over foraging. New Queens and males are produced late in the season and leave the colony and mate. Worker yellowjackets, males, the old queen, and colony dies usually by the first frost. The nest is not reused.

Yellowjackets can be divided into two groups. The first (Aerial Yellowjackets and Bald (or white) faced hornets) nest in exposed places (such as hanging from the eaves of a building or in the branches of a tree) and never scavenge meat or dead things. Their nests look like gray Chinese paper lanterns and may contain 100 to a 1000 or more workers. The second group (3-5 common species in southwestern British Columbia) nest in cavities or in the ground and often contain 1000's of workers. They are the ones seen coming out of holes and scavenging meat at a picnics. They can become abundant in the late summer and fall. Their hidden nests look similar to the exposed nests but are more brittle. The paper is made by pulling on the fibers of exposed wood such as fences and stumps and chewing the fiber into a pulp. One species makes paper from rotten wood and has tan nests.

Yellowjackets are defensive, and never attack unprovoked. You may not intend to step near their nest or take away their hamburger on your plate, but they define what is their space and react predictably to intrusions. A colony that has been disturbed is much more likely to defend itself. It is possible to sit next to an undisturbed yellowjacket nest and observe them quietly without any problems. The two groups differ greatly in their behavior- species that form large nests (most ground/ cavity nesters) will grab on to their victim with their mandibles as they repeatedly sting. Species with fewer individuals in a colony (the aerial/exposed nesters such as the Aerial yellowjacket and the bald-faced hornet) will fly at the perceived aggressor, sting and quickly depart.

All Hymenoptera lay eggs that produce males if the egg is not fertilized and females when the egg is fertilized. The Queen normally keeps workers from laying eggs. If the queen dies, the workers may start to lay eggs which will produce males- this may be an important source of genetic material for yellowjackets.

I study insects that attack yellowjackets- I am especially interested in some rare wasps that lay their eggs in Douglas fir and hemlock needles. Caterpillars (or sawflies) feed on the needles and (with the eggs inside them) are captured by yellowjacket workers and fed to the young yellowjacket larvae in the nest. 'My' wasp larvae then wait for the yellowjacket larva to start to pupate, and then eat the yellowjacket pupa. Adults look a little like a yellowjacket, but do not sting.

Other insects found in yellowjacket nests:

Small Parasitic Ichneumonid Wasp (Sphecophaga)- This small reddish non-stinging wasp enters yellowjacket nests and lays eggs in the yellowjacket pupae, feeding on them and killing them.

Lesser House Fly- (Fannia) This is the fly that quietly circles around the center of a room (or any enclosed space, such as under a tree) rather than banging against a window. Their very pretty white eggs are found on the paper on the outside of active and old nests in the ground. The larvae are scavengers.

Lesser Wax Moth- (Vitula) The pink larvae and their webbing are common in old weakened aerial yellowjacket nests.

Earwigs- Common scavengers in yellowjacket nests- often in nests high in trees.

For additional information please write me or check these references:

Pacific Northwest Yellowjackets

Akre, R.D., A. Greene, J.F MacDonald, P.J. Landolt, H.G. Davis. 1980. The yellowjackets of America North of Mexico. USDA Agriculture Handbook No. 552, 102 p.

Edwards, R. Social wasps : their biology and control. Rentokil, 1980.

Evans, H.E. and M.J. West-Eberhard. 1970. The Wasps. University of Michigan Press, Ann Arbor. 265p.

Miller, C.D.F. Taxonomy and distribution of Nearctic Vespula. Canadian Entomol. Society Supl. 22: 1-52.

Spencer, G.J. On the nests and populations of some vespid wasps. Proceedings of the Entomological Society of British Columbia 57: 13-15.

Spradbery, J.P. 1973. Wasps: an account of the biology and natural history of social and solitary wasps. Univ. Wash. Press, Seattle. 408 p.

Dedicated to Roger Akre, who first showed me yellowjackets.

The purpose of this paper is to give general information in terms that anyone can understand and enjoy. Exceptions and more technical terms could be given, but are not really necessary for understanding. Citations are available for some comments, but many are based on my own observation and inference.

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This page is maintained by Dave Carmean with an eye towards speed and clarity, and last modified July 1998. Comments or suggestions are welcomed!