The box elder bug, Boisea trivittata, is a common insect recognized by its distinctive markings. Adult bugs are about half an inch long, black or dark gray, with bright red or reddish-orange lines tracing the edges of the wings and thorax. Named for the boxelder tree, their primary host, they also feed on maple and ash trees. They become noticeable in late summer and early autumn when they leave host trees to search for a protected place to spend the winter.
Survival Strategy: Overwintering, Not Dying
Box elder bugs do not die during the winter; they enter a physiological state of inactivity known as diapause. This process is triggered by the shortening photoperiod, or daylight hours, of late fall. Diapause involves a significant slowdown of the insect’s metabolism, allowing them to remain dormant for months without needing to feed or reproduce.
To withstand freezing temperatures, the bugs employ an internal mechanism for cold tolerance. They synthesize and accumulate cryoprotectants, which act like a natural antifreeze within their body tissues, lowering the freezing point of their internal fluids. This adaptation helps prevent the formation of ice crystals that would otherwise cause fatal damage to their cells. Only mature adults possess the sufficient energy reserves and physiological capacity to successfully survive the winter.
The Winter Hideout: Where They Seek Shelter
As the weather cools, box elder bugs exhibit a strong tendency to aggregate in large clusters, a behavior that aids in their survival by maximizing warmth. These masses of insects seek out warm, sun-exposed surfaces, often clustering on the south and west-facing walls of buildings, which absorb the most solar radiation. This aggregation is a precursor to finding a permanent, sheltered overwintering location.
The adult bugs seek a dry space where the temperature will remain consistently cool, ideally between 40 and 50 degrees Fahrenheit. This range is warm enough to survive but cool enough to conserve stored energy. They utilize tiny cracks and crevices around window frames, door casings, and foundations to gain entry into protected voids. Once inside a structure, they commonly settle in wall voids, attics, or basements, where they remain inactive for the season.
If an overwintering bug finds its way into the heated living space of a home, it becomes mobile and active, mistaking the indoor warmth for spring. Their flat bodies allow them to squeeze through small gaps, leading them to cluster around interior windows and light fixtures. They seek a non-freezing shelter, not food or to cause damage.
Spring Emergence and Life Cycle Continuation
The overwintering period concludes when temperatures rise consistently in the spring, typically reaching 70 degrees Fahrenheit or higher. This warmth signals the end of diapause, prompting the bugs to emerge from their sheltered locations and move outdoors. Adults that spent the winter inside a structure attempt to exit, often clustering on sunlit windows as they try to leave.
Once outside, the primary objective of the newly emerged adults is to feed and replenish energy reserves depleted during their dormant state. They feed on the tender leaves, flowers, and seeds of host trees, like the boxelder, to prepare for reproduction. After feeding, females deposit their reddish eggs in bark crevices or on foliage, starting the next generation.