Over a 29 year period on Cape Cod Massachusetts there were 5 fall outbreaks of adult Ixodes dammini and a crash following an outbreak year. These outbreaks were proceeded by 2 years with normal November December temperature and winters with limited frozen bare ground. The crash was proceeded by a winter with an extended period of frozen bare ground. The range of this tick is limited to the coastal area with a normal average November December mean at or above 2.8-degrees-C, a period critical for the development of the spring adult cohort for this tick with a summer adult diapause. The below normal November December means from 1959 to 1973 on upper Cape Cod was a period of very low infestation of fall adult I. dammini.