FURTHER OBSERVATIONS ON THE MOLTS OF THE OX 
BOTS HYPODERMA BOVIS DE GEER AND H. LINEATUM 
VILLERS 1 
By E. W. Laake 
Entomologist , Investigations of Insects Affecting the Health of Animals , Bureau of 
Entomology , United States Department of Agriculture 
INTRODUCTION 
In a paper * published by the writer the conclusion was reached that there are 
five stages or four molts in the larvae of Hypoderma lineatum Villers and probably 
the same number in H. bovis De Geer. These conclusions have been generally 
accepted as presented by the writer but they have been questioned by some 
entomologists who hold to the older theory of the occurrence of only three stages 
or two molts in the case of Oestridae as well as other Diptera. The purpose of 
the present paper, therefore, is to present further facts substantiating the claim 
that there are five larval stages in these two species of Hypoderma. 
The writer’s paper referred to above, setting forth the larval characters for 
each stage, was brief, and merely the general differences of the cephalopharyngeal 
skeleton, mouth parts, and spinous armature of each species were given. 
The confusion in the larval stages lies in the earlier ones, that is, first, second, 
and third. The first stage as hatched is well known, as are also the last two 
stages in the back of the host. Some maintain that the larvse have no molt 
from the time they leave the egg and enter the skin of the host until they reach 
the subdermal tissues of the back approximately eight months later, during 
this time having increased in length from less than 1 mm. to from 13 to 16 mm. 
COMPARISON OF CHARACTERS OF FIRST THREE LARVAL STAGES 
IN HYPODERMA LINEATUM 
For the purpose of comparing some of the more outstanding characters of 
each of the first three larval stages as described by the writer, three larvae of 
each stage taken at random out of a large series of cleared and mounted speci¬ 
mens of Hypoderma lineatum were subjected to a microscopic examination, the 
characters of each instar carefully noted, and measurements made and averaged 
for the three specimens of each instar. These averages are presented in Table I. 
The characters noted in the table constitute measurements of the cephalopharyn¬ 
geal skeleton with mouth hooks, the number of spines in the group immediately 
below the mouth, the spines on the ventral side of the eighth segment and those on 
the anal segment, including the flattened or triangular spines on the border of 
the posterior spiracles. The eighth segment was chosen for special study be¬ 
cause the diameter of the larva is near its greatest at this point and the counts 
and measurements of spines can be made with greater accuracy and ease than 
on the smaller segments. 
» Received for publication March 21, 1924. 
1 Laake, E. W.—distinguishing characters or the larval stages of the oxwarbles hypoderma 
BOVIS AND HYPODERMA LINEATUM, WITH DESCRIPTION OF A NEW LARVAL STAGE. JOUT. AgT. Research 21: 
439-457, illus. 1921. 
Journal of Agricultural Research, 
Washington, D. C. 
( 271 ) 
Vol. XXVIII, No. 3 
April 19,1924 
Key No. K-129 
