Warble fly
Hypoderma spp.
Warble fly
If you see a fly that fits the description below, call Biosecurity New Zealand's Exotic Pests and Diseases hotline on 0800 80 99 66.
Two species of Warble flies affect domestic cattle in the Northern Hemisphere: Hypoderma lineatum, the common cattle grub, and H. bovis, the northern cattle grub.
Adult warble flies are hairy and are about the size of small bees with yellow-orange abdomens.
Eggs of warble flies are about 1 mm long and are fixed to the hairs of the host by small terminal clasps, especially on the animal's legs, but more rarely on the body as well. The eggs hatch in four to seven days and the larvae crawl down the hair to the skin, which they then penetrate. In doing so, they cause considerable irritation. The total duration of the life cycle is approximately a year, with the major portion of this time being spent in the body of the host.
Impacts
Although the normal hosts of common cattle grub are cattle and Old World deer, they have been known to parasitize horses and humans. The common cattle grub is also known to parasitize American bison. Goats and sheep are occasional hosts, but full development is not completed in these hosts.
When flies approach to lay eggs the cattle become nervous and attempt to escape the attack by running away, and will even go into water. As the flies are persistent, the animals are constantly irritated and do not feed properly, which results in an appreciable loss of weight and decrease of milk yield. The animals may also hurt themselves severely, or at least become wounded and damage their skins.
The larvae irritate the tissues around them, causing the flesh to become greenish-yellow and infiltrated, especially along the tracks where the larvae have wandered, and thus depreciated in value. Great damage is caused to the hide by the perforation produced. The annual loss due to this factor alone is very high in some countries.
Distribution
Warble flies occur naturally in cattle in at least 50 countries in North America, Europe, Africa, and Asia, but principally in the region of 25 and 60 degrees latitude in the Northern Hemisphere. The southern limit is reached in the Punjab of India, Libya, northern Mexico and Hawaii. In the United States, common cattle grub ranges from northern Mexico to northern Canada, with the exception of south Texas and Alaska.
Management
Management techniques used to control Warble flies include:
- Mechanical removal of larvae – Mature larvae may be squeezed out of the warble swelling.
- Insecticide treatment – Use of systemic organophosphorous insecticides.
- Use of an antiparasitic compound – avermectins (a chemically modified form of a fermentation product of Streptomyces avermitilis.
Page last updated: 22 October 2008