The brown marmorated stink bug (Halyomorpha halys), a shield-shaped insect native to Asia, is a widespread agricultural and nuisance pest. This insect often invades homes in the fall, leading many to wonder about its resting habits. Stink bugs do not “sleep” at night in the same way that mammals do. Instead, they enter a state of inactivity with a reduced response to stimuli, which is fundamentally different from true sleep.
How Insects Rest
Insects do not experience the complex, regulated sleep cycles, such as REM and non-REM stages, that characterize mammalian sleep. The period of reduced activity insects undergo is described as quiescence or rest. This state is marked by prolonged immobility and decreased responsiveness to external stimuli.
Behavioral quiescence allows the insect to conserve energy when foraging or mating is not practical. This rest period is regulated by their internal biological clock, the circadian rhythm. Crucially, insect rest is rapidly reversible, allowing the bug to quickly resume activity if disturbed.
The Stink Bug Daily Activity Pattern
The brown marmorated stink bug follows a daily cycle that defines its periods of activity and rest. Stink bugs are primarily diurnal, meaning their most active periods occur during the day. This time is devoted to essential behaviors like foraging for food, flying, and mating.
As the sun sets, stink bugs enter their nightly state of quiescence. They seek sheltered spots to remain still and conserve energy, and their movement significantly decreases during the dark period. This inactivity is a temporary rest period that can be easily broken if they are disturbed or exposed to a light source. This short-term, cyclical pattern differs significantly from their long-term seasonal dormancy.
Seasonal Inactivity and Overwintering
The long periods of stillness observed in stink bugs are not daily rest but a deeper, seasonal state of dormancy known as diapause. Diapause is a pre-programmed, hormone-regulated condition that allows the adult bugs to survive the winter. It is triggered by environmental cues, primarily the shortening of the day length, or photoperiod, in the fall.
As days shorten, adult stink bugs cease reproductive development and suppress their metabolism to conserve resources. This preparation is why they aggressively seek protected, secluded areas, such as inside human-made structures, starting in September and October. They remain in this non-feeding, non-reproductive, and mostly motionless state throughout the winter.
The brown marmorated stink bug is chill-intolerant, which is why it invades homes to overwinter. The bug remains dormant until increasing temperatures and longer day length in the spring trigger its emergence. Adults then leave their overwintering sites to find food and resume their reproductive life cycle outdoors.