Friday, April 23, 2010

The Bugs Go In, The Bugs Go Out, The Bugs Play Pinochle on Your Grout

Have you noticed bugs on the inside of your windows this spring? It could be you’re part of an annual ritual – the Running of the Bugs! Every spring, bugs that took shelter in your house when the weather got cold, collect at the windows trying to get back outdoors. The good news is if you let them out, they’ll leave happily. The bad news is, they’re children will be back in the fall!

Oregon has several species of insects that make the indoor-outdoor run each spring and fall. Large groups can cluster together in attics, wall voids and other protected nooks and crannies. Most homeowners have likely met one or more of them. Only one is an Oregon native, the rest are non-native invasive species. Here is the lineup:

1.) Boxelder Bug – 1/2 inch long, black with red markings. Outdoors in the summer feeding on maple trees. Collects on houses with southern exposure in the fall, then move indoors for the winter. Native.

2.) Brown Marmorated Stink Bug – 5/8 inch long, brown with faint white markings around the back edge and on the antennae. Live outdoors in the summer feeding on a variety of fruits and vegetables. Moves indoor in cold weather. Invasive species, native to Asia. Becoming more and more common in Portland and spreading to neighboring communities.

3.) Multicolored Asian Lady Beetle – bigger than regular ladybugs, 1/4 to 1/3 inch. Many different color patterns from red-orange and no spots to 20 spots. Live outdoors feeding on insects in the summer. Collects in sheltered nooks and crannies in the winter. Asian species, intentionally introduced for biological control in the 1960’s and 70’s. Thought to be displacing native species.

4.) Cluster Fly – larger than a regular housefly, 1/3 inch. Gray/black and slow moving. Live outdoors in the summer where they parasitize earthworms. Move indoors with cool weather. Native to Europe.

There are others, but these are the common ones. None of these insects bite, transmit disease, or harm houseplants. They are just nuisances. The best way to deal with these indoor-outdoor migrants is to keep them from entering your house in the first place. The more cracks and crevices you caulk, the fewer uninvited guests you’ll have spending the winter in your cozy house.


  1. I can't stand when cluster flies get into my house!

  2. I'm finding at least one BMSB in my home every few weeks.

  3. I've often wondered, are all those ladybugs for sale in garden stores native or non-native and potentially invasive? Should we be trying to educate garden centers on the importance of our native ladybugs? Not to mention the terrible cost, annoyance, and stink that large outbreaks of invasive ladybugs have caused elsewhere.