Effect of Length of Day on the Activity and Hibernation of the American Dog Tick, Dermacentor Variabilis (Say) (Acarina: Ixodidae)

Abstract

The American dog tick ( Dermacentor variabilis (Say)), vector of Rocky Mountain spotted fever in the Eastern States, is a species of rapidly increasing economic importance. A point of more than ordinary interest in a consideration of its biology is the question of what factors induce hibernation. On the island of Martha's Vineyard, Mass., both larval and adult ticks hibernate in large numbers, whereas the number of nymphs that hibernate may be large or small, varying from year to year. From the end of March or the middle of April (depending on the temperature) until the end of September larvae and nymphs are active in seeking their hosts, as indicated by the large numbers on meadow mice and deer mice. From October to March they are in hibernation, no ticks occurring on mice in severe winters and only occasional specimens being found engorging in mild winters; but in the vicinity of Washington, D. C, hibernation of larvae and nymphs is less complete. The season of adult tick activity is from April to the end of August, and hibernation of the adults is complete, both at Martha's Vineyard and at Washington.