Many residents of the US are familiar with the box elder bug, an orange and black bug found on box elder trees in summer and found in homes in the late fall and winter as it looks for a sheltered place to spend the winter. True bugs that invade homes in summer in large numbers are uncommon. US residents may become familiar with a new species of red and black bug, the Elm Seed Bug, Arocatus melanocephalus.
The Elm Seed Bug was not considered a pest anywhere until 1999, when residents of Northern Italy complained about home invasions by large numbers of these bugs. The largest outbreaks of home invasions occurred in late May in the years 2001-2003. Every year since, invasions have been reported in different locations in Italy. Some evidence suggests that the home invasions are correlated to spells of unusually hot weather.*
Like many Seed Bugs, the Elm Seed Bugs overwinter as adults, mate in spring and lay eggs on elm trees. The larvae feed on the fruits and seeds in May-June in Italy, and become adults in summer. Like most true bugs, the Elm Seed Bug has scent glands that produce a noxious odor, that deters predators. When crushed, the bugs produce an unpleasant odor.
Insects that invade homes in large numbers are prime candidates for global transport by hitchhiking in the baggage of travelers. Recently, the Elm Seed Bug has appeared in Southwestern Idaho. The bug is not expected to cause damage to Elms or have large ecological impact. Whether or not it becomes a nuisance or spreads around the US remains to be seen. The USDA/APHIS is asking the public in Idaho to be on the look out for this pest to help determine the extent of its spread.
*Maistrello, et al. 2006. Journal of Thermal Biology. Volume 31, Issue 8, Pages 594–598.