Late Summer Yellowjackets Bugging You?

by Jack DeAngelis, PhD of LivingWithBugs.com

Late summer is the time for yellowjackets and mosquitoes. Populations of these pesky insects start to peak around August and then decline by October when the weather turns cool (obviously we're talking about the northern hemisphere). The pattern for both, and some other insects as well, is that populations are very low in spring, build through early summer, peak in late summer and decline to almost zero by winter. We'll deal with mosquitoes in a later article. For now let's talk about yellowjackets and paper wasps and what to do abut them.

Yellowjacket Colony Life Cycle

For most species of yellowjackets the only life stage that survives the winter is the fertilized queen. All other stages die in late fall and nests are not re-used. Queens start new colonies in the spring. Spring weather has a significant impact on nest initiation. Cold, wet weather suppresses nest development while warm, dry weather helps nest establishment. Once nests are started worker yellowjackets provision and defend them. Nests grow throughout the summer so by late August they are at maximum size.

Types of Yellowjackets and Nests

There are many species of yellowjackets. Most are predators and make relatively small nests. These species are not often encountered. A few species, however, are notorious as scavengers (not predators). These species also tend to make larger and more threatening nests. These are the yellowjackets that cause the problems. Yellowjacket nests come in two basic types - above ground, or aerial, and below ground nests. They are structurally identical the only difference is that one is in an underground cavity.

Control of Yellowjackets

In order to reduce the number of bothersome yellowjackets you should reduce the number of nests of scavenger species in your area. Unfortunately, while the familiar yellowjacket traps are useful as decoys (see www.livingwithbugs.com/yellow.html), they are not effective for controlling nests. There are really only two ways to control nests and one of them is no longer available.

If you locate a troublesome nest you can effectively control it with a “wasp & hornet” spray. Don't use gasoline or other flammable liquid. Using gasoline this way is illegal and dangerous! In the evening treat the nest opening with the "wasp & hornet" spray. If possible cover the opening with a rock or soil (ground nests). Use about a half can of spray per treatment. Some ground nests may require a second treatment.

The other method is poison baiting. The idea here is to trick workers into taking a bit of poisoned bait back to the colony to feed to nestmates and the queen. The advantage with this method is that you don't need to know where the nest is in order to control it. Unfortunately the only insecticide that was registered for this use in the US is no longer available. Work is underway to find a new toxicant for poison baiting. Perhaps by next year this method will again be available.

Control of Paper Wasps

Most of the time paper wasps can be left alone - they make small, non-threatening nests. Paper wasps (Polistes) are distinguished from yellowjackets (Vespula) by the following body features: paper wasps generally have a thinner “waist” between the thorax and abdomen and longer hind legs. The biggest difference, however, is the way they construct their nests. Yellowjackets make a closed nest with a single opening. The nest is completely covered by a papery envelope. Paper wasps make an exposed nest, without a paper envelope, where you can clearly see the individual cells.

Paper wasps generally make small nests in out-of-the-way places. Also, since paper wasps are predators they won't be a nuisance at picnics - unless you are serving live insects! The European paper wasp (Polistes dominulus), however, is a little different. This wasp is not native to the US and in recent years populations have exploded from coast to coast. This wasp also builds large nests often in areas where people may contact them. By sheer numbers and nest placement this wasp has become a real pest in the US. Unfortunately we don't yet have good solutions to bring the numbers down. Paper wasps are not attracted to wasp traps used for yellowjackets.

The hope for European paper wasps is that soon a natural enemy (predator or parasite) or a pathogen will “find” this non-native species and begin to bring populations under natural control. Until this happens control nests as you encounter them with “wasp & hornet” sprays. For more information, including photos of nest structure, see www.LivingWithBugs.com/epw.html.

For additional information and related articles visit www.livingwithbugs.com.

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