warble fly

Ox Warble-fly (Hypoderma bovis)

young warbles

Squirrel infested with warbles

Warble fly is a name given to the genus Hypoderma, large flies which are parasitic on cattle and deer. Other names include "heel flies", "bomb flies", and "gad flies", while their larvae are often called "cattle grubs" or "wolves." Common species of warble fly include Hypoderma lineatum (horse), Hypoderma bovis (cattle) and Hypoderma tarandi (reindeer) .

Adult warble flies are large, hairy and bee-like; brown, orange or yellow in color. The adults have vestigial mouthparts and so do not feed during their short lifespan, which can be as little as five days.^[1]

They are found in all continents of the northern hemisphere, principally between 25 and 60 degrees latitude.

Infestations

The fly will lay eggs on the foreleg of the affected cattle. These will be ingested by licking, and be swallowed. Internal cycle involves the passing oesophagus muscles and spinal cord before subcutaneous re-emerging.

When they re-emerge, the larvae cause many swellings ("warbles") under the skin, causing some harm to animals, but not as a general disease. It doesn't burrow into the flesh, but stays under the skin (hence, its scientific name Hypoderma). Nevertheless, when accidentally destroyed by pressure, the larvae can cause large purulent swellings.

From the subcutaneous swelling, the warble will puncture the skin when coming out of the bovine. From those numerous holes, the hide is rendered valueless.

The migrating larvae can cause damage to meat as the tunnels they make fill with a substance known as butcher's jelly.^[1] Growing livestock may have a lower daily weight gain. Milk yields may also suffer, but in adult cows, the infestation is generally limited, due to immunisation following the first infestation, as a calf.

Warble fly has been eradicated in many countries, beginning from Denmark and Western Germany, in the 1960s. They have also been eradicated from the United Kingdom, ^[2] as well as from Belgium. The method was the pour-on application of an organophosphorus compound.

From the 1980s, the preventive treatment is easier, by subcutaneous use of Ivermectin, but the warble fly remains present in North Africa.

See also

• Bot fly
• Horse-fly

References

External links

• common cattle grub on the UF / IFAS Featured Creatures Web site