Do bot flies, Cuterebra (Diptera: Cuterebridae), emasculate their hosts?

Abstract

Asa Fitch, in his description of a new species of Cuterebra that he named, "emasculator," was the first to suggest that bot flies castrated their mammalian hosts. In recent years, several major review papers and parasitology texts have continued to perpetuate this belief. A review of both the primary literature on bot flies and their hosts and of the life cycles of both bots and hosts provides no evidence to substantiate castration. Eastern Chipmunks (Tamias striatus) experimentally infected with Cuterebra emasculator experienced no destruction of testicular tissue. The concept of castration may have been perpetuated by observations of bots in the scotal sac of a host. Superficial examination of a host with a bot(s) in the scrotum would suggest that the bot had consumed the testis; this is demonstrated on a White-footed Mouse (Peromyscus leucopus). We conclude that there is no evidence to support the notion that bot flies castrate their mammalian hosts. On extremely rare occasions, a bot may slightly displace a testis, and perhaps this temporarily reduces fertility.