Large aggregations of insects — a crop of periodical cicadas, overwhelming hatches of mayflies, or the sudden synchronous appearance of many colonies of winged ants — are most often a summertime phenomena. But fall can be an excellent time to observe — even without intending to — equally impressive bunches of bugs. Within the last few days in my region, the annual assemblege of Eastern Box Elder Bugs (Boisea trivittatus) has begun.
Despite the ubiquity of Box Elders (Acer negundo) around here, I don’t see boatloads of Box Elder Bugs most of the summer. As the name suggests, they feed primarily on Box Elders, but will also utilize other maples. Box Elder Bugs (let’s call them BEBs) are Hemipterans, or true bugs, with piercing mouthparts. They suck juices from young leaves and stems, but really prefer the newly developing seeds of A. negundo. Since Box Elders are dioecious (male and female flowers are on separate trees), large populations of BEBs really only occur on female Box Elders, which have all the seeds. BEBs rarely do any damage to trees.
Mature BEBs are about 12 mm long. BEBs overwinter as full-grown adults, so now is the time of year when they begin looking for sheltered places in which to hibernate. First they gather en masse on or near tree trunks. Then they may fly up to two miles prospecting for a cozy, dry location to pass the winter months. In nature, rock piles or loose bark might do the trick, but buildings also offer excellent refugia. BEBs wedge their way under shingles, into vents, and various other cracks and crevices. If it has been a warm, dry summer — like this one in the Midwest — there might be thousands of BEBs on the sunny sides of buildings, just taking a break from their search, or looking for entry into an appropriate hibernacula. When they get into residential buildings, people get all freaked out, although they are completely harmless to humans.
Although I have an enormous geriatric female Box Elder in my yard, I have few BEBs, and none have ever sought sanctuary in my house. They have, however, begun to accumulate on the outside walls of our campus parking structure. Many will crawl under light fixtures and signs, to emerge on warm winter days to bask a little before retreating once again. On these brisk winter afternoons, I welcome the sight of these handsome little bugs, with their pleasing geometric pattern of black and red. Their tentative exploration of a January thaw provides a reminder of the richness and plenty of summer during a time of year when that fecundity seems furthest away. I like to think that perhaps, like me, they turn themselves to the winter sun, and imagine the lush abundance of a summer past, and one yet to come.