Agriculture and Agri-Food Canada Insect Identification
sheet No. 22 October 1982
The warble fly, or heel fly, is a major pest of cattle in the
Northern Hemisphere. There are two species: the common cattle
grub, Hypoderma lineatum , and the northern cattle grub, Hypoderma
bovis. Both occur in Canada.
The egg-laying activities of warble flies terrifies cattle into
running or gadding, which interferes with normal grazing, reduces
milk flow and somearial causes injuries. On hatching, the larvae
(grubs) burrow through the skin and migrate through the body until
reaching the animal's back where they produce the characteristic
lumps, or warbles. Each warble has a breathing hole made by the
grub and these injuries somearial lead to infection. In moving
through an animal's body, the grubs may injure its esophagus and
affect its ability to eat, resulting in loss of weight, or they
may injure its spinal cord, causing paralysis. Infected animals
have lower market values because of carcass trimming required and
because of damaged hides for leather.
warble fly has a black, hairy body marked with yellow to orange
stripes and resembles a small bumblebee. The flies are active
in the spring and early summer, when each female lays about 600
eggs on the hairs of an animal's legs, belly and flanks. The
adult fly of the common cattle grub is about 1 3 mm long and
appears in May and June; that of the northern cattle grub is about
2 cm long and appears in June and July. The tiny, barely visible
eggs hatch in 2 to 7 days and the young grubs penetrate the animal's
skin and begin moving through its body, reaching its back about
7 to 9 months later. Here they remain for about 2 months until
fully developed, by which time their color has changed from white
to dark brown or black. On reaching maturity, the grubs emerge
from the warbles and drop to the ground to pupate. Adult flies
appear in 1 to 2 months.
is no practical method of killing the adult flies or preventing
them from laying eggs on cattle, control measures must be directed
at the grubs. Consult your provincial Agriculture Department
hominis, the human botfly, is a major pest of warm
blooded animals, including man, throughout the American tropics.
Although there have been some research efforts to support the idea
of an eventual eradication of this pest, not much has been accomplished
on this idea because of the difficulty in artificial rearing it.
Although the USDA may have partially supported some of this research,
there has never been any major campaign to control it; except the
control afforded by acaricides applied for tick control. The USDA
and the Mexican and Central American countries are engaged in a
major campaign to eradicate the primary screw worm, Cochliomyia
hominivorax (already eradicated from all countries North of Honduras;
the plans are to eradicate it all the way to Panama and establish
a permanent, biological barrier in Panama).
As to Dermatobia hominis, one of the best review papers is: Sancho,
E. 1988. Dermatobia, the Neotropical warble fly. Parasitology Today.
4:242-246. This paper cites 45+ papers on this insect.
Alberto B. Broce Kansas State University Department of Entomology
W est Waters Hall Manhattan, KS 66506 voice (913) 532-4745 FAX
(913) 532-6232 firstname.lastname@example.org
There are two fascinating
recent articles on these flies. The first is a confirmation of "bacon therapy" for
the removal of the larvae from humans, Brewer et al, J Amer Med
Sco 270, 2087-2088
(Nov 1993) and an account of the mating behavior of related Cuterebra
flies in the Western US in the Fall 1994 American Entomologist,
153-160 by Paul Catts.
Hugh M. Robertson Associate
Professor Department of Entomology University of Illinois 505
S. Goodwin Urbana, IL 61801 Phone (217)
333-0489 FAX (217) 244-3499 Email "email@example.com"