Infestation of yellow jackets

Asked May 5, 2014, 11:29 AM EDT

Hello,
We have had some swarming of yellow jackets (I believe they are not bees) in and around our property in the last few days. The scary thing about it is that there are lots of them (reminded me a little of Alfred Hitchcock's "The Birds") and they were inside of our house both evenings. The next morning, they were on the floor dead. Then it happened again the following evening. This morning, they are swarming the bird bath and scaring our birds away. Half of them have drowned. I read a little information about them and it sounds like we could have real problems by the end of the summer.
We live in a 1912 home that has a fairly new roof but could have holes on some of the walls, and we have lots of woodpiles around our property... is this causing part of the problem? What should we do? I don't mind a yellow jacket here or there but this is more company than we feel comfortable with!
Thank you for your help.

Denver County Colorado integrated pest management urban integrated pest management yellow jackets

1 Response

In spring, the overwintering queens of various kinds of wasps emerge from their winter shelter sites and become active on warm days. (Winter is spent whereever they can find a sheltered spot, not atypically behind walls where an opening made it an available cavity.) Each of them will be attempting to establish a new nest; most will be unsuccessful in this. (Cold, wet spring weather, such as last week's storm, likely will suppress some the success of establishing nests.) I suspect that the large number found in the home were all overwintered queens that had been behind the walls of the home or were poking around the yard looking for nest sites, and a window or other opening allowed them to come inside.

These days, along the Front Range, the most visible of the wasps active in spring in in yards is the European paper wasp: http://www.ext.colostate.edu/pubs/insect/05611.html It is quite similar in size to the yellowjackets but is a bit more slender bodied and its hind legs are long and trail when in flight. The European paper wasp is a predator of live insects, rearing its young on living insects (particularly caterpillars). Since it began colonizing the Front Range a bit more than a decade ago it has had enormous impact in reducing caterpillars in yards/gardens (e.g., cabbageworms, hornworms). The nests they make are often seen (single layer, multi-celled paper nests) hanging under eaves, in cavities, etc. Fortunately,however, they are not scavengers and do not disrupt outdoor dinging (as do certain yellowjackets) and generally leave people alone unless the nest is accidentally and severely provoked.

Yellowjackets, specifically the species of yellowjacket known as the western yellowjacket, presents different and more serious potential problems: http://bspm.agsci.colostate.edu/files/2013/03/Yellowjackets.pdf These are the most important stinging insect of the region. They are notorious scavengers and readily visit areas of outdoor dining. Nests are constructed out-of-site, usually underground, so people not infrequently come too close to the nest and get stung.

The fact sheets referenced above discuss both of these types of wasps and the control options. For the latter there is not alot that can be done. On the other hand the occurrence of large numbers of wasps at this time of year is not a very good predictor of how many we will have at the end of the year. Instead it better reflects how many were produced at the end of last year and have survived. And, since only a small percentage of the overwintering survivors successfully make a nest, and size of successful nests can be greatly affected by summer conditions, a lot can happen to determine how serious they may be in your yard this summer.