Boxelder bug nymphs make a colorful garden display

In the case of boxelder bug nymphs in gardens, red does not mean danger.

Boxelder bug adults and nymphs. Photo credit: William M. Ciesla, Forest Health Management International,
Boxelder bug adults and nymphs. Photo credit: William M. Ciesla, Forest Health Management International,

Within the next month or two, some Michigan gardeners will be surprised and possibly frightened by many small, red insects sunning themselves in their gardens. Michigan State University Extension horticulture educators and Master Gardener hotlines will talk to people who have seen “the red menace.” What gardeners are finding are boxelder bug nymphs in their favorite flowers and plants.

Obviously, a group of red insects attracts attention. They can be found on rocks and mulch, sitting quietly and soaking up the rays. The nymphs, or juveniles, are bright red with only a bit of black trim. As they grow to adulthood, their body color changes from red to dark gray with red pin striping around the wings and body. Adult boxelder bugs are approximately one-half inch in length.

The concern is that there is some nefarious purpose planned for the landscaping. However, this is one of those events where it is not necessary to do anything other than stop and stare. Boxelder bugs (Leptocoris trivittatus or Boisea trivittatus) are common in areas that have boxelder trees. This means the tree does not have to be on your property or the neighbor’s; it may be as much as a half mile away. This insect is called a true bug or Hemiptera. True bugs are sucking insects, and the boxelder bug feeds on the flowers and seeds of the tree from which it gets its name. Boxelder bugs suck the gooey goodness out of boxelder tree flowers and leaves and appear not to damage any other landscaping.

In the fall when the first cold nights and warm days happen, insects that overwinter, or spend the winter as adults, begin looking for a location to sleep away the winter. This crowd could include boxelder bugs as well as western conifer seed bugs, multicolored Asian lady beetles, cluster flies and possibly brown marmorated stink bugs. They gravitate to the south and west sides of homes because these are the warmest sides. They slowly squeeze themselves into cracks and openings and head for the wall void, which is the space between the outer wall and the inner wall. The only decision to make after that is which side of the wall insulation to hibernate. During early spring, sunny days warm the wall interior and semi-conscious insects think spring has come and squeeze out the nearest crack. As many people have discovered, they turn left instead of right and end up on a windowsill or wall indoors.

In the spring, the adults leave the wall voids and return to the shining leaves, warm temperatures and bug excitement. Eggs are laid on trunks, branches and leaves of their favorite kind of tree. Soon, a new generation of boxelder bugs is born. They are bright red with black wing pads on their backs and are only one-sixteenth of an inch long. In late spring or early summer, they have hatched and are wandering around in groups.

Smart gardeners know to appreciate that touch of temporary color they offer and then get back to pulling weeds.

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