The boxelder bug, Boisea trivittata, is a common nuisance insect known for congregating in large numbers on and within homes as the weather cools. Temperature is the primary environmental factor that dictates their survival, movement, and life cycle. Understanding the precise thermal limits of this insect is the clearest way to predict its behavior and implement effective control strategies. This knowledge includes the low temperatures that cause mortality and the high temperatures that can be used for extermination.
Lethal Low Temperatures and Mortality
Boxelder bugs are cold-tolerant insects, but their survival depends entirely on successfully entering a sheltered, semi-dormant state known as diapause. The temperature at which a boxelder bug dies from cold exposure is a range influenced by the duration of the cold and the bug’s level of acclimatization. The point where the bug’s body ceases all coordinated movement and enters a cold-induced paralysis is called the Critical Thermal Minimum (CTmin).
The Lower Lethal Temperature (LLT) is the point of sustained exposure that leads to death, which is usually well above the temperature where body fluids freeze. Prolonged exposure to temperatures consistently below \(10^{\circ}\text{F}\) to \(14^{\circ}\text{F}\) will cause mortality, especially for bugs exposed outside of an insulated shelter. Insects that are not fully cold-acclimated or cannot find adequate cover are susceptible to freezing injury at these temperatures.
The true, absolute death point for the boxelder bug is its supercooling point (SCP), the temperature at which its internal body fluids spontaneously freeze. Boxelder bugs produce cryoprotectant chemicals, which act as a natural antifreeze to depress this freezing point. For insects in the Hemiptera order, the supercooling point can range from approximately \(-10^{\circ}\text{F}\) to \(-15^{\circ}\text{F}\) in their fully winterized state. Death at this extreme low is instantaneous because the formation of ice crystals destroys cellular structures. The most significant factor for mortality is not the SCP, but rather the failure to find refuge from continuous, moderately cold temperatures.
Temperature Range for Activity and Shelter Seeking
The thermal environment dictates when boxelder bugs are active and when they begin their fall migration toward human structures. Activity generally begins in the spring when temperatures consistently rise above \(50^{\circ}\text{F}\), allowing them to emerge from overwintering sites to feed and reproduce. They remain active throughout the summer, but the population surge and subsequent home invasion occur in the autumn.
The shift toward seeking shelter is triggered by the shortening of daylight hours combined with falling temperatures. As temperatures begin to drop into the \(45^{\circ}\text{F}\) to \(60^{\circ}\text{F}\) range, adult boxelder bugs begin to aggregate in preparation for diapause. This temperature threshold initiates their mass movement toward warm, sunny surfaces, particularly the south or west sides of buildings.
The bugs look for a crack or crevice where the temperature will remain stable, ideally between \(40^{\circ}\text{F}\) and \(50^{\circ}\text{F}\), to survive the winter. This moderate range is warm enough to prevent freezing yet cool enough to keep their metabolism slow and conserve energy reserves. They are not truly hibernating, but rather entering a state of reduced activity where they do not eat or reproduce. If a warm, sunny day occurs mid-winter, a small rise in temperature can activate them, causing them to emerge from wall voids or attics inside the home.
Using Extreme Heat as a Control Method
While cold temperatures can kill boxelder bugs naturally, the application of extreme heat offers a practical method for targeted control. Boxelder bugs have a low tolerance for temperatures above \(115^{\circ}\text{F}\) to \(120^{\circ}\text{F}\). Exposure to these high temperatures causes rapid dehydration and denaturation of cellular proteins, leading to death.
One effective, non-chemical method utilizes boiling water to kill bugs clustered on exterior surfaces like foundations or sidewalks. Hot water must be at least \(165^{\circ}\text{F}\) to \(180^{\circ}\text{F}\) to be effective for rapid extermination on contact. This temperature is significantly higher than the bugs’ natural thermal tolerance and causes immediate mortality.
For bugs found indoors, a vacuum cleaner is the recommended method of removal. The vacuumed bugs should be sealed inside a container and exposed to heat for certain death. Placing the sealed bag or container in direct sunlight can quickly raise the internal temperature above the lethal threshold, ensuring the bugs are killed rapidly and do not escape to re-infest the structure later.