Yellow jackets can turn nasty in the fall

Why are yellow jackets so aggressive in the fall? And is that really a yellow jacket you see, or is it a honeybee or a hornet?

Yellow jackets are actually wasps, with yellow and black markings on both their bodies and faces. If you see a similar insect that is black and white, it is likely a bald-faced hornet, while honeybees have hairier bodies, which is why they are such good pollinators.

Another fact you may not want to test personally is that honeybees can sting only once, while a yellow jacket can sting repeatedly. Nevertheless, yellow jackets do have several redeeming qualities. For one thing, they are important predators of pest insects, especially when the pests are in the caterpillar stage. Think tomato hornworm, petunia budworms and even our now-famous fall webworms.

Yellow-jacket colonies are annual affairs, as only a fertile queen survives the winter. In late spring, she emerges, selects a nest site in a tree, shrub, soil cavity like an abandoned rodent run, or other protected, hollow place. She then chews wood fiber into a paper-like pulp to make a place to lay her eggs. The queen cares for the first young larvae for about three weeks.

At that point, she is undoubtedly tired from all that work, so turns the baby-care chores over to the young hatchlings and spends the rest of her summer laying eggs. The number of yellow jackets in the nest keeps building, and by early fall there could be a few thousand residents, most of them workers.

The developing larvae need protein, so the workers go out in search of it, which they find in the form of insects, rotting meat of animals or your sandwich. With all those hungry mouths back home to feed, this helps explain why yellow jackets become aggressive, unwelcome guests at your picnic or campsite. The adults, however, eat mostly sugars, which is why they like your soda and watermelon, and fruit that has dropped off the trees.

Sometimes, of course, yellow jackets build a nest in a place inconvenient to us, or become so hungry for our hamburgers that we need to control them in some way. While their sting is painful, it is usually the result of the yellow jacket getting caught, perhaps in your pants leg or shirt. To avoid being stung, do not swat at a wasp. Also, try not to jump, yell or run, as these behaviors will be interpreted as aggressive and may prompt attack.

Use a trap for temporary control of yellow jackets. An aerosol that propels a stream of insecticide several feet, and is specifically for yellow jackets, will kill those living in the nest. Use the spray in the evening, when the yellow jackets are likely to be at home. But do keep in mind that they are very beneficial, and spray them only if they are truly causing a problem. When freezing temperatures come, they'll be gone, anyway. Except for the queen, of course, who will get busy next spring, repeating the cycle.

Coming up: It's not too soon to mark your calendar for the 13th annual "Winter Dreams — Summer Gardens" gardening symposium on Saturday, Nov. 5. The all-day event, sponsored by Oregon State University Extension and Jackson County Master Gardeners, will be held at the RCC/SOU Higher Education Center in Medford. Attendees can choose four of the 40 classes offered for a day of learning about a variety of gardening topics. Call 541-776-7371 to receive a list of classes and a registration packet.

Carol Oneal is a past president of the OSU Jackson County Master Gardeners Association. E-mail her at

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