Invaders at Your Picnic

I love to eat outdoors. Whenever the weather permits, my wife and I eat on our deck -- except during the late summer and early fall during yellowjacket season. My wife heads indoors with the arrival of the first annoying wasp. I’m no help. Rather than shoo them away, I’m always trying to get a good look at them to identify the species. Luckily, she loves me anyway!

Our most common picnic crasher has been the “western yellowjacket,” Vespula pensylvanica. Yeah, I know Pennsylvania isn’t in the West. A Swiss fellow, Henri Louis Frédéric de Saussure, named the species in 1857. Maybe Pennsylvania seemed pretty far west to him. Anyway, this species is the most common pest species in much of the real West. The “common yellowjacket,” Vespula vulgaris, a little smaller and darker in color, is also a notorious scavenger. These species are native to our area and usually build their nests underground.

A new invasive species has recently joined the picnic crashers. This European species known as “German yellowjacket,” Vespula germanica, is spreading throughout Oregon. It was introduced to the East Coast in the middle of the last century and has been spreading west ever since. It showed up in Oregon in the early ‘90s. At first populations were scattered in Ontario, Portland, and Tillamook. There hasn’t been a survey in recent years, but it appears to be widespread now.

German yellowjackets are no worse than our native species as picnic pests, but they don’t seem to displace the natives either, so there are just more types of yellowjackets to bother us now. The German variety is more likely to nest in above ground spaces, including wall voids and attics. Huge indoor colonies have been reported in other places where this invasive species has moved in. Stay tuned – it could happen here too.

Another unfortunate consequence of the German yellowjacket invasion has to do with Oregon Christmas trees. Yellowjacket queens often choose to hide in bushy Christmas trees after the weather cools off in the fall. Hawaii, Mexico, and other markets for Oregon Christmas trees don’t want new species of yellowjackets hitchhiking across their borders. Regulations for these markets require mechanical shaking to dislodge the queens. It is an added expense for our growers, but it is a good idea.

Yellowjackets have their place in nature’s web, but human-aided yellowjacket spread is not a good thing. If you take meat or sweet food outside this time of year, a yellow and black European visitor with a stinger may remind you of that fact.

Dan Hilburn