behavioral evidence for this mosquito being a different species from "c. pipiens" comes from research by kate byrne and richard nichols. the species have very different behaviours, are extremely difficult to mate, and with different allele frequencies consistent with genetic drift during a founder event. more specifically, this mosquito, "c. molestus", breeds all-year round, is cold intolerant, and bites rats, mice, and humans, in contrast to the above-ground species, which is cold tolerant, hibernates in the winter, and is considered to mostly feed on bird hosts. when the two varieties were crossbred, the eggs were infertile, suggesting reproductive isolation.