YELLOWJACKETS AND OTHER SOCIAL WASPS Integrated Pest Management in and around the Home Only a few of the very large number of a single queen who overwinters and wasp species in California live a social becomes active when the weather life; these species are referred to as warms. She emerges in late winter/ social wasps. Some social wasps are early spring to feed and start a new predators for most or all of the year nest. From spring to midsummer nests and provide a great benefit by killing are in the growth phase, and the larvae large numbers of plant-feeding insects require large amounts of protein. and nuisance flies; others are exclu- Workers forage mainly for protein at sively scavengers. Wasps become a this time (usually in the form of other problem only when they threaten to insects) and for some sugars. By late sting humans. One of the most trouble- summer, however, the colonies grow some of the social wasps is the yellow- more slowly or cease growth and re- jacket. Yellowjackets, especially quire large amounts of sugar to main- ground- and cavity-nesting ones such tain the queen and workers. So as the western yellowjacket (Fig. 1), foraging wasps are particularly inter- tend to defend their nests vigorously ested in sweet things at this time. when disturbed. Defensive behavior Figure 1. Western yellowjacket. increases as the season progresses and Normally, yellowjacket and paper colony populations become larger wasp colonies only live one season. In while food becomes scarcer. In fall, very mild winters or in coastal Califor- Dolichovespula [=Vespula] maculata) on foraging yellowjackets are primarily nia south of San Francisco, however, the abdomen, and have a very short, scavengers and they start to show up some yellowjacket colonies survive for narrow waist (the area where the tho- at picnics, barbecues, around garbage several years and become quite large. rax attaches to the abdomen). cans, at dishes of dog or cat food placed outside, and where ripe or over- Yellowjackets Nests are commonly built in rodent ripe fruit are accessible. At certain The term yellowjacket refers to a num- burrows, but other protected cavities, times and places, the number of scav- ber of different species of wasps in the like voids in walls and ceilings of enger wasps can be quite large. genera Vespula and Dolichovespula houses, sometimes are selected as nest- (family Vespidae). Included in this ing sites. Colonies, which are begun IDENTIFICATION AND group of ground-nesting species are each spring by a single reproductive LIFE CYCLE the western yellowjacket, Vespula female, can reach populations of be- In western states there are two distinct pensylvanica, which is the most com- tween 1,500 and 15,000 individuals, types of social wasps: yellowjackets monly encountered species and is depending on the species. The wasps and paper wasps. Yellowjackets are by sometimes called the “meat bee,” and build a nest of paper made from fibers far the most troublesome group. Paper seven other species of Vespula. Vespula scraped from wood mixed with saliva. wasps are much less defensive and vulgaris is common in rotted tree It is built as multiple tiers of vertical rarely sting humans. They tend to shy stumps at higher elevations and V. cells, similar to nests of paper wasps, away from human activity except germanica (the German yellowjacket) is but enclosed by a paper envelope when their nests are located near becoming more common in many ur- around the outside that usually con- doors, windows, or other high traffic ban areas of California, where it fre- tains a single entrance hole (Fig. 2). If areas. quently nests in houses. These wasps the rodent hole is not spacious tend to be medium sized and black enough, yellowjackets will increase the Nests of both yellowjacket and paper with jagged bands of bright yellow (or size by moistening the soil and dig- wasps typically are begun in spring by white in the case of the aerial-nesting ging. Similar behavior inside a house PEST NOTES Publication 7450 University of California Agriculture and Natural Resources Revised August 2001 August 2001 Yellowjackets and Other Social Wasps clothing. As with any stinging incident, it is best to leave the area of the nest site as quickly as possible if wasps start stinging. Paper Wasps Paper wasps such as Polistes fuscatus aurifer, P. apachus, and P. dominulus are large (1 inch long), slender wasps with long legs and a distinct, slender waist (Fig. 3). Background colors vary, but most western species tend to be golden brown, or darker, with large patches of Figure 3. Paper wasp. yellow or red. Preferring to live in or near orchards or vineyards, they hang their paper nests in protected areas, such as under eaves, in attics, or under tree branches or vines. Each nest hangs like an open umbrella from a pedicel (stalk) and has open cells that can be seen from beneath the nest (Fig. 4). White, legless, grublike larvae some- times can be seen from below. Paper Figure 2. Yellowjacket nest in spring wasp nests rarely exceed the size of an (top), summer (center), and early fall outstretched hand and populations (bottom). vary between 15 to 200 individuals. Most species are relatively unaggres- sive, but they can be a problem when Figure 4. Paper wasp nest. sometimes leads to a wet patch that they nest over doorways or in other develops into a hole in a wall or areas of human activity, such as fruit ceiling. trees. wasps will crawl into soda cans and cause stings on the lips, or inside the Immature yellowjackets are white, Mud Daubers mouth or throat. grublike larvae that become white pu- Mud daubers are black and yellow, pae. The pupae develop adult coloring thread-waisted, solitary wasps that Responses to wasp stings vary from just before they emerge as adult wasps. build a hard mud nest, usually on ceil- only short-term, intense sensations to Immatures are not normally seen un- ings and walls, attended by a single substantial swelling and tenderness, less the nest is torn open or a sudden female wasp. They belong to the family some itching, or life-threatening aller- loss of adult caretakers leads to an Sphecidae and are not social wasps but gic responses. All these reactions are exodus of starving larvae. may be confused with them. They do discussed in detail in Pest Notes: Bee not defend their nests and rarely sting. and Wasp Stings (see “References”). Of Aerial-nesting yellowjackets, Dolicho- During winter, you can safely remove specific concern is a condition that vespula arenaria and D. maculata, build the nests without spraying. results from multiple-sting encounters, paper nests that are attached to the sometimes unfamiliar to attending eaves of a building or are hanging from INJURY OR DAMAGE health professionals, that is induced by the limb of a tree. The entrance is nor- Concern about yellowjackets is based the volume of foreign protein injected mally a hole at the bottom of the nest. on their persistent, pugnacious behav- and the tissue damage caused by de- These aerial nesters do not become ior around food sources and their ag- structive enzymes in wasp venom. Red scavengers at the end of the season, but gressive colony defense. Stinging blood cells and other tissues in the they are extremely defensive when behavior is usually encountered at body become damaged; tissue debris their nests are disturbed. Defending D. nesting sites, but scavenging and other breakdown products are arenaria sometimes bite and/or sting, yellowjackets sometimes will sting if carried to the kidneys, to be eliminated simultaneously. Wasp stingers have no someone tries to swat them away from from the body. Too much debris and barbs and can be used repeatedly, es- a potential food source. When scaveng- waste products can cause blockages in pecially when the wasp gets inside ing at picnics or other outdoor meals, the kidneys, resulting in renal insuffi- N 2 N August 2001 Yellowjackets and Other Social Wasps ciency or renal failure. Patients in this it-yourself options include trapping frequently because yellowjackets are condition require medical intervention, wasps in a baited trap designed for not attracted to rotting meat. Also, even dialysis. that purpose, early-season removal of periodically check the trap to remove nests, or spraying the nest or nesting trapped yellowjackets and make sure MANAGEMENT site with an insecticide labeled for that workers are still attracted to the trap. Most social wasps provide an ex- use. tremely beneficial service by eliminat- Water Traps. Water traps are generally ing large numbers of other pest insects Trapping Wasps homemade and consist of a 5-gallon through predation and should be pro- Trapping wasps is an ongoing effort bucket, string, and protein bait (turkey tected and encouraged to nest in areas that needs to be initiated in spring and ham, fish, or liver works well; do not of little human or animal activity. Al- continued into summer and fall, espe- use cat food because it may repel the though many animals prey on social cially when the yellowjacket popula- yellowjackets after a few days). The wasps (including birds, reptiles, am- tion was large the previous year. In bucket is filled with soapy water and phibians, skunks, bears, raccoons, spi- spring there is a 30- to 45-day period the protein bait is suspended 1 to 2 ders, preying mantids, and bald-faced when new queens first emerge before inches above the water. (The use of a hornets), none provides satisfactory they build nests. Trapping queens dur- wide mesh screen over the bucket will biological control in home situations.