The Box Elder Beetle

Class - Insecta Order - Heteroptera Family - Rhopalidae

The conspicuous black-and-red box elder bugs are divided into two species. Box elder bugs undergo gradual/simple metamorphosis. The eastern species grows to be about 1/2” long; it is distributed as far west as Nevada, while the slightly smaller western species ranges in California and Oregon. These elongate-oval bugs lay eggs in the spring basically on female or pod-bearing box elder trees.

The young nymphs are bright red. Dark markings become more apparent on older nymphs. Eastern nymphs feed primarily on the female Box elder tree (Acer negundo, Linnaeus) foliage, tender twigs, and winged seed pods. The Western box elder bug primarily feeds on Acer macrophyllum (another box elder) other maples, almonds, apples and other fruit. In late summer, mature nymphs and adults crawl down the tree trunk by the hundreds and disperse. Adults also fly directly from the tree into houses. Like attic (cluster) flies, the bugs find spaces under siding, around window and door facings where they enter wall voids and rooms in houses.

Box elder bugs seek overwintering shelter outdoors in tree hollows, as well as in sheds, barns and houses. Those that find harborage indoors move around and fly on warm winter days.

Habitat Alteration

The best management method is to find at least any/all female box elder trees and remove them. These “trashy” trees are seldom planted as ornamental shade trees; they seed themselves and grow as weed trees, and are not eliminated mainly because they are difficult to identify. Their branches break easily in storms, they have messy seeds and are short-lived. Their leaves, somewhat like maples, are variably shaped on the same tree. Seed pods are helpful in the identification of the female trees. It usually takes a large invasion before tree removal is practiced.

Caulk around entry points on the building foundation and door and window facings. At times it may be necessary to caulk other points of entry indoors. Lightly dust with food-grade DE.