Native Pests and Invasive Species

Periodically, ants invade my kitchen. They like our compost bucket and my multi-grain Cheerios. Like most entomologists, I have a relatively high tolerance for bugs, but I draw the line at ants in my cereal. The most common house ant in this area is the odorus house ant, Tapinoma sessile. These small black ants are attracted to moisture and sweets; that’s why they like kitchens. Interestingly, they are not an invasive species; odorus house ants are native. We invaded their territory, not the other way around.

In fact, most of the ants we have in Oregon are native, and thankfully most of them prefer outdoor living. There are exceptions, the pavement ant (Tetramorium caespitum), a recent introduction here, is another home invader. Argentine ant, Linepithema humile, and red imported fire ant, Solenopsis invicta, have also been collected in Oregon, though  the former has a very limited distribution and the latter is not known to be established. Both are well known invasive pests in other regions.

Another common Oregon house guest, the western boxelder bug, Leptocoris rubrolineatus, is a second example of a native insect that acts like an invasive species. Boxelder bugs invade homes in the fall. During spring, they appear again at windows trying to find their way outdoors. Except for being a nuisance, they are not harmful. In contrast, the brown marmorated stink bug, Halyomorpha  halys, does the same indoor/outdoor thing but is a serious pest of fruits and vegetables; it is a bonafied invasive species.

The world of weeds provides other examples. Western juniper, Juniperus occidentalis, can be quite invasive, but it’s homegrown. Salt cedar, Tamarix aphylla, has similar invasive tendencies, but is not from around here. Both can be aggressive invaders.

Early spring is the season where bedstraw (Galium) grows like gangbusters in my yard. It is coming on strong in my wildflowers meadow right now. I don’t like pulling it because it sticks like velcro to gloves. My wife get a rash when she handles it. Some bedstraws are native, others are not. One of these days I should get this particular species identified. To me it’s a weed, but it might be a common native known as cleavers or sticky willy, Galium aparine. I think it is easier for me to curse it, spray it, and pull it if I imagine it being an invasive species. No doubt that is why I haven’t bothered to bring in a sample. If that sticky nasty stuff turned out to be a native Oregon wildflower, I’d just cry—as I continue to curse it, spray it, and pull it . . . .

Dan Hilburn