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Fact Sheets: Commonly Observed and Asked About Insects and Spiders Found in Alberta

Box Elder Bug (Boisea trivittatus)

Box Elder Bug
Adult Box Elder Bug
Credit: Terry Thormin

Aggregation of Box Elder Bugs
Part of an aggregation of Box Elder Bugs showing both adults and immatures. The adults are darker and have wings
Photo CD 0023 3291 1601, Image #41 - Credit: John Acorn


Although the official name for this insect is the Box Elder Bug, most Albertans call it the Maple Bug. The reason: it feeds on the Box Elder Tree, but in Western Canada this tree is known as the Manitoba Maple.


This is a medium-sized (11 - 14 mm) bug that is black with red markings. Unfortunately this describes a lot of different insects. The photograph will help eliminate most other bugs, but keep in mind this photo shows both adults and immatures; the immatures are smaller and redder and lack wings. This is a true bug, with piercing, sucking mouthparts.


The Box Elder Bug is restricted to the prairies in Alberta. It is widely distributed in North America east of the Rockies from southern Canada south.


Although the young can be found by mid-summer, the adults usually appear by late summer and can survive until quite late in the fall.


The Box Elder Bug feeds extensively on Manitoba Maple or Box Elder, sucking up the sap and weakening the tree. This may result in leaf mottling and premature leaf drop. This insect overwinters as an adult and tends to congregate in large numbers for this purpose. At times it can be numerous on sunnier walls of houses and can become a nuisance if individuals find a way into the house.


Where they occur, the Large Milkweed Bug (Oncopeltus fasciatus) and Smaller Milkweed Bug (Lygaeus kalmii) could easily be confused with the Box Elder Bug. They have more extensive red or orange markings on them and feed exclusively on various species of milkweed. They also never congregate in large numbers in the fall.


When present in large enough numbers Box Elder Bugs can do damage to Manitoba Maple trees. Most people call us in the fall because they are curious about the large numbers on the walls of their houses or concerned about the numbers that are getting in the houses. Washing them off the walls of the house with a blast of cold water from a hose may help. The only way to ensure that they do not get inside the house is to fill in all cracks where they could be getting in, a rather daunting and expensive task.

For more information on controlling Box Elder Bugs when they reach pest numbers, please go to the following website http://www.unexco.com/boxelder.html

Note: We cannot provide advice on controlling insect pests. If you need more information beyond what has been provided here, we suggest you either search further on the web, or talk to a local exterminator.

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Last update: August 19 2004