First report of the mating behavior of a species of Frog-biting midges (Corethrellidae:Diptera)

Swarming is the most common mating behavior shown by lower flies (Nematocera). This mating aggregations have been observed in the wild and in laboratory colonies of mosquitoes (Culicidae) and phantom midges (Chaoboridae) but is assumed to be absent in their sister taxa, frog-biting midges (Corethrellidae). Corethrellidae is a monogeneric family that includes over 100 species of frog-biting midges (Corethrella spp). In contrast to mosquitoes, female frog-biting midges find their host by eavesdropping on the mating calls of anurans to obtain a blood meal for egg development. Here we study the previously unknown mating behavior of frog-biting midges.  We video recorded the mating behavior of individuals in a laboratory colony of Corethrella appendiculata and analyzed their swarms to characterize it. Contrary to previous speculations, we report that frog-biting midges aggregate in mating swarms. We thoroughly characterize such formations describing size and duration of the aggregation, sex ratio of the swarm, flight patterns of individual midges, influence of light intensity on the formation of swarms and use of swarm markers. Additional swarms were analyzed in detail to determine pairing and copulation patterns. We determined that males and females meet in the air and fall together out of the swarm onto the floor. Copulation takes place in venter to venter position and we confirmed that virgin females are inseminated after pairing with a male at the swarm. Overall, we reveal the mating behavior of frog-biting midges for the first time fulfilling critical gaps in information about the reproductive biology of this family.