Thrips are minute, slender insects often noticed swarming in the air. These creatures, measuring between 1 to 2 millimeters in length, are part of the order Thysanoptera, a name derived from Greek words meaning “fringed wings.” They are commonly referred to as “thunderbugs” or “storm flies” due to their frequent mass appearances, particularly around times of unsettled weather.
The Mechanics of Thrips Flight
Thrips employ a distinctive flight mechanism known as “clap and fling.” Their wings are narrow and strap-like, featuring a fringe of long bristles along their edges. This unique structure is an adaptation for navigating through air that, at their small scale, behaves more like a viscous fluid.
During the “clap” phase, thrips bring their wings together over their back, creating a circulation of air that generates lift. As the wings then rotate around their trailing edges and separate in the “fling” motion, air rushes into the newly formed gap, establishing additional vortices. This action generates further force, allowing thrips to “swim” through the air. The fringed wings can expand their effective surface area during flight, further aiding in lift production.
Reasons for Thrips Swarming
Thrips swarming is linked to specific environmental conditions. Mass flights often occur on warm and dry midsummer days, aligning with the ripening of various crops. Dispersal flights can also be triggered by sudden drops in atmospheric pressure or changes in temperature.
Research indicates that peak thrips dispersal occurs when temperatures range between 20.8°C and 27.7°C, with flight activity decreasing significantly above 30.6°C. This swarming behavior serves a biological purpose, aiding in the insects’ dispersal to locate new food sources or find mates. While traditionally associated with thunderstorms, the sudden appearance of thrips at ground level during thundery weather may actually be a result of them landing from higher air layers, possibly influenced by changes in atmospheric electricity rather than the storm itself initiating flight.
Attraction and Nuisance Factors
Thrips exhibit a strong attraction to particular colors: yellow, blue, and white. This preference explains why they frequently land on light-colored clothing, window screens, or outdoor furniture. Beyond visual cues, thrips are also drawn to moisture, such as human perspiration, especially during periods of hot and dry weather.
The carbon dioxide humans exhale can also attract these insects, causing them to fly towards faces or land on exposed skin. While thrips can “bite” humans, this action is a minor irritation and not a cause for medical concern. These “bites” are an attempt by the thrips to feed or obtain moisture, and they are not known to transmit diseases to humans.