We have combined aircraft and airborne Doppler radar observations to show that microinsects in the atmospheric convective boundary layer (CBL) are concentrated in rather well-defined plumes, that these plumes are generally found in thermals of rising air, and that the insects in those plumes oppose the updrafts at a rate that increases as the updrafts become stronger. In this paper, a simple numerical simulation of the airflow field and insect concentration in the CBL is developed. The model shows a consistency of the observed insect flight behavior with the presence of well-defined insect plumes in the otherwise well-mixed CBL and with the tendency of insects to cluster in updrafts. The model also explains the growth of insect plumes in the morning hours and their disappearance in the late afternoon. Other studies have proposed that the response of insects to being lofted high into the CBL is controlled by air temperature. Our simulation shows that a temperature-sensitive response alone does not yield well-defined plumes in regions of rising air currents. The observed flight strategy may be counterintuitive, but we suggest that it has a clear adaptive advantage.