Ask a Master Gardener: Uninvited picnic guests with stingers!
Published 5:00 pm Tuesday, September 12, 2006
QUESTION: I’ve never seen the yellow jackets so aggressive. Last weekend they forced us to move the family picnic indoors. Is there anyway to discourage them?
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ANSWER: Yellow jackets and paper wasps are beneficial insects. They feed their young numerous insects that ordinarily damage shade trees and crops. They also kill countless houseflies and blowflies. Unfortunately, in late summer and early fall they become more aggressive and dangerous as their populations peak, they scavenge for meat and sweets and become pests, especially at picnics. A few people (1 to 2 percent) are severely allergenic (hypersensitive) to yellow jacket venom and a sting can be life threatening.
Foraging yellow jackets are often mistaken for honeybees by the untrained eye because of their similar appearance and the fact that they are sometimes attracted to the same food source. Honeybees are slightly larger than yellow jackets and are covered with hair or setae, which are absent on yellow jackets. Foraging honeybees can be identified by the pollen baskets on the rear legs that are often loaded with a ball of yellow or green pollen. The yellowjacket has a smooth stinger that can be used to sting multiple times, whereas the honeybee has a barbed stinger that can be used to sting only once.
In the Pacific Northwest, yellowjackets and paper wasps have annual colonies. The only colony members to overwinter are inseminated queens, which spend the winter in protected locations, such as under bark, in stumps and logs, and within stacks of firewood. They also frequently overwinter in attics of homes.
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The parent colony begins to dwindle in fall and the foundress queen and all workers die with the onset of cold temperatures.. A new colony cycle begins the next spring. When colonies begin to die, skunks and bears dig into the underground nests and feed on the immature yellow jackets. Above-ground nests will persist in dry areas, but they are rarely used again the next spring.
Yellow jackets are known for their presence around beehives in the fall and will enter and rob honey if given the opportunity. They can become a major stress around weak honeybee colonies that cannot protect their food stores.
The diet of adult yellow jackets consists mainly of food rich in sugars and carbohydrates, such as plant nectar and fruit. Also, foraging adults search for meat that is high in protein, such as insects and fish which they chew and condition in preparation for larval consumption. The larvae in return secrete a sugary substance that is consumed by adults. This exchange of food between the adults and larvae is known as trophallaxis.
In late summer and fall, yellow jackets scavenge for alternate food sources which many times leads to major conflicts with human activities. Large numbers of these pesky insects can totally disrupt a picnic as they are attracted to carbonated beverages, juices, candy, ham, bologna, fish, cakes fruit, vegetables and ice cream.
Remember yellow jacket colonies do not normally survive the winter, and the first hard freeze will eliminate most colonies. It might be necessary occasionally to destroy a yellow jacket nest because it’s near human activity. Treat nests at night with an aerosol insecticide. Treating at night helps because workers are inside and relatively calm. Use one of the aerosols that propel a stream of insecticide 20 feet so that you can stand off a safe distance and treat directly into the nest opening.
A crude yellow jacket trap is made by hanging a raw fish or piece of liver (slightly diced on the exterior) by string about 1 to 2 inches above a container of detergent and water. The detergent will act as a wetting agent and eliminate surface tension which will improve trap efficiency. Foraging yellow jackets will be attracted to the raw meat and will often become overloaded with food and fall into the water and drown. This method of yellow jacket control is not as efficient as nest elimination, but it may help reduce the population to acceptable levels.
EDITOR’S NOTE: For answers to local gardening questions, contact Master Gardener Rachel Gana at 642-8723 or e-mail her at: baiter1@pacifier.com.