The increased incidence of biting fly activity prior to precipitation is a commonly observed phenomenon. Several factors contribute to this behavior, primarily related to atmospheric changes and the flies’ instinctual drive to feed and reproduce before unfavorable weather conditions arrive.
This behavior ensures the flies obtain necessary nourishment before a period where foraging may be difficult or impossible. The atmospheric pressure drops frequently associated with impending rain can trigger increased activity in many insects, including biting flies. This preemptive feeding allows them to build energy reserves, potentially improving their survival and reproductive success during and after the rain event. Historically, this observation has been noted anecdotally and has formed part of traditional weather lore.