Friday, August 03, 2007

Why are some yellowjacket wasp nests dangerous?

Yellowjacket wasps are social insects that live in large, highly organized colonies (left). Yellowjacket wasps construct nests made of papery material that are either suspended above ground (aerial nests, left) or buried below ground level (ground nests). Another social wasp, the paper wasp, builds smaller, less threatening nests.

Yellowjacket wasp nests may harbor thousands of individual worker wasps by late summer and early fall at the peak of activity.

Life cycle of a wasp nest

Nest construction begins in the spring when an inseminated queen emerges from winter hibernation. Nests start small but grow rapidly as new workers (sterile female daughters of the queen) are reared. Nests reach maximum size by late summer and early fall. As winter approaches new queens and a few male drones are produced. After these reproductives mate the males die and the newly-mated queens leave the nest. All of the current-year workers abandon the nest and die by the time cold weather settles in. Most yellowjacket nests therefore only last a single season.

What do wasps eat?

Almost all yellowjacket wasps capture live prey, mostly other insects, but a few species scavenge already dead animals or even plant material. Some yellowjackets seek the sweet, liquid honeydew produced by feeding aphids. Those species that will feed on dead animal tissue are called scavenger species and these are the ones that harass us during picnics or at other outdoor events.

Two scavenger species are the most common worldwide. Vespula vulgaris and V. germanica probably account for the greatest percentage of problems between these social wasps and humans. In the western US, western Canada and Hawaii, V. pensylvanica is commonly encountered in many areas and is extremely abundant in some areas. V. maculifrons is the dominant species in the mid-west, south and eastern US.

Defending their nests

Yellowjackets are highly defensive and can become quite aggressive when their nest is approached. Swarms of angry workers can be released from both aerial and ground nests if the nest is disturbed. Any vibration or loud, low-frequency noise, such as power lawn equipment, can provoke this swarming behavior.

Yellowjackets are most likely to be dangerous in late summer and early fall when their numbers peak. Ground nests are generally more dangerous than aerial nests because they are harder to see until you are literally standing on top of one.

How to destroy a threatening nest

Most wasp nests should be left alone. As predators wasps are considered to be beneficial insects in that they prey on many pest species. However, in late summer and fall a nest that is located near an area of human activity such as a garden, playground or picnic area may need to be destroyed to avoid the dangers of accidental contact.

If a threatening aerial or ground nest needs to be destroyed the safest approach is to use a Wasp & Hornet type spray (see link below for details) and treat the nest from a safe distance. Unfortunately none of the commercial traps are effective for destroying individual nests and poison baits are no longer available.

[safe ways of removing threatening nests]