DISTINGUISHING CHARACTERS OF THE LARVAE 
STAGES OF THE OX-WARBLES HYPODERMA BOVIS 
AND HYPODERMA LINEATUM, WITH DESCRIPTION 
OF A NEW LARVAL STAGE 
By E. W. Eaake 1 
Scientific Assistant, Investigations of Insects Affecting the Health of Animals , Bureau 
of Entomology, United States Department of Agriculture 
Since it has been unquestionably shown that the two species of Hypo- 
derma are of great economic importance on account of the injuries 
caused by the larvae or grubs in perforated hides, the loss of flesh, and 
diminished milk production of cattle, it is important that more be 
known about their morphology in order that they may be distinguished 
readily in all stages. 
The purpose of the present paper is to show the value of the posterior 
stigmal plates and other characters for differentiating the four larval 
stages previously known and to describe a new larval stage of Hypo- 
derma lineatum De Villiers. In making a careful study of the larvae it was 
found that very reliable characters existed for distinguishing larvae of H. 
lineatum and H. bovis De Geer. Separation of these two species in the last 
two stages was found to be easy by comparison of the form and structure 
of the posterior stigmal plates. The character of the spiny armature, 
which was first described by Brauer and which has been entirely relied 
upon by all investigators up to the present time for the distinguishing 
of the species, is good only for the last or fifth larval instar; while the 
characters of the stigmal plates permit, with absolute certainty,. the 
differentiation of the fourth as well as the fifth larval instar. 
The stigmal plate is a complicated structure, and it will be considered 
here only in so far as it is of importance in differentiating the two species 
in question. J. C. H. De Meijere (8) 2 has given an admirable descrip¬ 
tion of the details of structure and functions of the posterior stigmal 
plates of H. bovis. 
The plates vary greatly in the different stages of development and to a 
considerable extent in the same stage. There may even be a marked 
variation between the two spiracles on the same specimen. Variable 
as they may appear, however, there are always certain definite associated 
characters which can be relied upon for each species. 
1 The author wishes to express his thanks and appreciation to Mr. E. C. Bishopp, Entomologist, Investi¬ 
gations of Insects Affecting the Health of Animals, Bureau of Entomology, for his help and suggestions in 
many ways in carrying out these studies; to Mr. H. B. Bradford, Artist, Bureau of Entomology, who 
executed the drawings of figures 5 to 23, inclusive; and to Mr. R. W. Wells, Scientific Assistant, Bureau 
of Entomology, for valuable material collected in various parts of the United States. 
2 Reference is made by number (italic) to “ Literature cited,” p. 456-457. 
Journal of Agricultural Research, 
Washington, D. C. 
yg 
Vol.XXI, No. 7 
July 1, 1921 
Key No. K-97 
(439) 
