March, 1922. Tlp' Insh Naturalist. 25 



THE LARVAL MOUTH-HOOKS OF HYPODERMA. 



BY GEOFFREY PHIBBS, 



The larvae of the two species of warble fly, Hypoderma 

 bovis, De Geer, and Hypoderma Uneatum (Vill) have long 

 been known to pass through four stages before pupation. 

 \Vith the recent demonstration by E. W. Laake (4) of the 

 Bureau of Entomology, United States Department of 

 Agriculture, that two distinct stages are included in what 

 had previously been known as the '* second" instar, five 

 stages, at least must be recognised in the larval history of 

 the " warble-flies." Laake points out that the second 

 instar has rows of minute spines on the segments, while the 

 third is entirely smooth except for the spines at the mouth 

 and those on the tail segment. He is mistaken, however, 

 in supposing that his second stage larva " has not been 

 recognised before." It was briefly described and roughly 

 figured by Carpenter and Prendergast (i) in 1909. I am 

 greatly indebted to Mr. Laake for generously sending 

 beautifully mounted specimens of American larvae of 

 Hypoderma in these tw^o stages. 



When newly hatched from the Q^g the young Hypoderma 

 larva is, perhaps, less than one-thirtieth of an inch long. 

 At the end of the fifth stage when nearly ready to pupate 

 it may be over an inch in length, and half an inch in 

 diameter. Between the first stage and the last the mouth 

 parts undergo considerable modification. 



In the newly hatched larva the mouth armature is very 

 conspicuous and relatively large. In the first stage, as 

 also in the second (Figs, i, 2, and 3) and third stages, it 

 consists of a horny somewhat lozenge-shaped spine {p>. s.) 

 situate between, and in the same plane as the two chitinised 

 mouth-hooks {h). These hooks lie with their backs to the 

 central spine and with their tips coming to a level with its 

 extremity. On either side of the base of the spine, which 

 projects backwards some way beyond the hooks, is the 

 beginning of a long oarTike pharyngeal sclerite (ph. s.). 

 These two sclerites, narrow near the mouth and broadening 

 towards their bases may be nearly a quarter as long as the 



