Two species of cattle grubs affect domestic cattle in the Northern Hemisphere. These are the common cattle grub, Hypoderma lineatum (Villers), and the northern cattle grub, H. bovis (Linnaeus). Adult cattle grub are commonly known as heel flies, warble flies, bomb flies, or gad flies.
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."fliesparasiticcattledeer
Adult warble flies are large, hairy, and bee- like and brown, orange, or yellow in color. The adults have vestigial mouthparts, so do not feed during their short lifespans, which can be as little as five days
Adults: The adults measure about 12-14 mm in length. The flies are hairy, with no functional mouthparts, and must mate and reproduce solely on the energy derived from stored reserves. Duration of the life span is three to five days. The hairs on the head and the anterior part of the thorax are yellowish-white. The abdomen is covered with light yellow hairs anteriorly, followed by a band of dark hairs, and the posterior portion bears orange-yellow hairs. Wings with black veins
The fly lays eggs on the forelegs of large animals. They are ingested when the animal licks them off. The larvae travel to the skin surface and cause swellings called "warbles". They remain under the skin, and when destroyed by pressure, the larvae can cause large purulent swellings or anaphylaxis. Upon emergence, the fly leaves holes in the skin. Large numbers of such punctures can render cattle hides valueless.purulent
The migrating larvae can cause damage to meat, as the tunnels they make in the muscle fill with a substance known as "butcher's jelly".Infestations also hinder weight gain and growth in the animals. Milk yields may also decline. Most infections in adult cows are minor due to immunity developed over time.
Veterinary Significance When the flies approach to lay eggs the cattle become nervous and attempt to escape the attack by running away, and will even go into water. Because 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.
The losses produced are: reduction of milk secretion, which is estimated at from 10 to 20 percent of the normal yield loss of weight due to the increased activity by the animals in escaping from the flies and the irritating larvae depreciation of the value of the carcass, which becomes greenish yellow and jelly-like in appearance at the points where the grubs are located and unfit for consumption injury produced to the hide which becomes "grubby" or full of holes where the grubs emerged.