The Blue Bugs of Autumn
by Carol Mack, WSU Pend Oreille County Extension
Every fall we (and other inland northwest communities) are briefly treated to a cloud of fluttery little gray-blue insects. Known as smoky-winged ash aphids, Prociphilus americanus, they are a nuisance, but harmless to humans except for the sneezes they cause as we breathe them in.
Like many aphids, these insects have a a life history that alternates between two different host plants. For most of the summer these aphids have been living underground, sucking the juice from fir tree roots. During this time, they have multiplied asexually (like a sci-fi movie, individuals occasionally split open to release new daughter aphids) They gather in wax-covered colonies that are often tended by ants collecting honeydew. In the fall, male and female winged forms emerge from the ground and seek out ash trees where they mate and lay eggs in the crevasses of the ash tree bark. Next spring, the eggs will hatch and the nymphs or baby aphids will crawl to the ash leaves and feed on sap until early summer when it's time to move back to fir roots.
So the hordes of small blue insects are just looking for love, this time of year. The numbers and duration of these clouds will depend on the weather—some years they are much more prevalent, but a freezing night spells a quick end to the swarms. Meanwhile, take a tip from the cross-country runners jogging by the Extension Office after school--close your eyes and pull your T-shirt up over your mouth to keep from choking as you pass through a swarm.