The boxelder bug (BEB) is a common and well-known insect in Iowa. Iowans are very familiar with the black-and-red adults that cluster on the south side of the house and invade during late fall in some years. It turns out, however, many are less familiar with the juvenile stage.
Boxelder bugs have a simple life cycle of three stages: egg, nymph and adult. The nymphs look similar to the well-known adults but are smaller and bright red because they don't yet have the black wings to cover their abdomen. The attached picture is of an older nymph with the black wing buds showing. Younger and smaller nymphs are more red with little if any discernable black markings where the wings will someday be.
During the summer months, BEBs live, feed and reproduce on trees, shrubs and other plants (including boxelders, maples, ashes and others). They feed on sap from their host plants but do not cause significant damage. Of interest this year is how many Iowans are noticing the bright red, soft-bodied nymphs in unlikely places such as in the lawn or flower beds, and on shrubs, sidewalks and driveways.
BEBs become nuisance pests in the fall when they leave the plants to find hiding places for the winter. During their random search, they congregate in the sunshine on the south sides of buildings, trees and rocks. From there they stray into houses through cracks in the foundation and siding, gaps along windows and doors, and other small openings.
It is not essential to control boxelder bug nymphs this early in the summer. These are not the same bugs that will invade the house in the fall. The nymphs present in June will mature into adults that will reproduce in July. It is this second generation of the summer that produces the accidental invader adults in October. The number that will be present in October is dependant on the upcoming weather, and killing some nymphs now will not make as much difference as will the weather in July.