Hypoderma lineatum ranges throughout North America, from Northern Canada to Northern Mexico. It is also found in Asia, Europe, and Africa. It is only rarely encountered south of 60 degrees latitude.

Biogeographic Regions: nearctic ; palearctic ; oriental ; ethiopian

Eggs are about 1 mm in length, slender, and white in color. At one end of the egg, there are small clasp-like structures that help anchor the egg to the animal hair upon which it was layed. Cattle grub larvae are true maggots, with retractable heads and no sclerotization or legs. After hatching from the egg, it is white in color. Pigmentation darkens (from white to yellow to light brown to black) as the larva matures and grows in size. The third instar is about 25 mm long with flat tubercles, small spines, and an obvious spiracular plate for respiration.

Pupae are coarctate, meaning that they are enclosed in a puparium. Puparium are black in color with an operculum, which is pushed open when pupation is over. Pupae are completely inactive.

The adult is hairy and has a distinctive yellow-and-black striped pattern, resembling a bumblebee. Like all insects, its body is divided into a head, a thorax, and an abdomen. It has a pair of functional wings and a pair of halteres posterior to the wings. Its mouthparts are vestigial and non-functional.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

The cattle grub, Hypoderma lineatum, inhabits dry areas where host animals (generally large mammals) are abundant.

Habitat Regions: temperate

Terrestrial Biomes: desert or dune ; savanna or grassland ; chaparral ; forest ; scrub forest

Other Habitat Features: suburban ; agricultural

Larvae are parasites of large mammals, primarily cattle. A first-instar larva makes its way through the subcutaneous connective tissue of its host by secreting three different digestive enzymes into the surrounding tissue, facilitating extracorporeal digestion. Nutrients are transported across the larval body wall into the hemolymph. Nutrients obtained during this stage in the life cycle are essential for the larva's significant growth. It also feeds on dead cells, pus, and other secretions that result from the immune response. This occurs within the cyst, also called a warble, that forms on the host's dorsal area due to the larva's presence.

Pupae are coarcate and inactive, meaning that they do not feed.

An adult H. lineatum does not feed during its short life span; it must rely on stored reserves for the energy needed for the process of reproduction.

Animal Foods: mammals; body fluids

Primary Diet: carnivore (Eats body fluids)

Warble flies can damage large mammal populations. At first, infected animals experience severe weight loss due to the intense action of gadding, where the animal may run around wildly trying to escape the ovipositing females, and which is believed to be stimulated by the buzzing of the flies. Secondly, the holes left by larvae do not heal over, therefore leaving the animal susceptible to other infections and opening up opportunities for myiasis by another kind of fly.

Species Used as Host:

• deer (Odocoileus)
• horses (Equus)
• bovids (Bovidae)
• elk (Cervus elaphus)

Little is known about predators of this species.

Little is known about communication and perception between warble flies other than that they have keen eyesight.

Communication Channels: visual

Perception Channels: visual

After the egg is layed, larvae hatch within one week. Larvae then burrow through the skin of the host into the subcutaneous connective tissue, to begin its first migration. It travels, from the initial site of penetration, through the connective tissue until it reaches the submucosa of the host's esophagus where it will stay and develop through the winter. As winter is ending, the larva (still a first-instar) migrates through the connective tissue from the esophagus towards the lumbar portion of the host where it will remain for one to two months. During this time, the larva molts twice and grows significantly. For respiration, the larva situates its posterior spiracular plate towards a hole that it cuts or eats through the hide of its host. The mature larva squirms its way out of the hole (warble) and drops onto the ground when it is ready to pupate. It then burrows into the ground where it will remain in its puparium for 3-6 more weeks, depending upon environmental factors such as moisture level (humidity levels greater than 10% impede the maturation process) and temperature. After the adult emerges from the puparium, it only has 3-5 days to reproduce and start the cycle all over again before dying.

Development - Life Cycle: metamorphosis

The life cycle of H. lineatum normally spans a year's time.

Average lifespan

Status: wild: 1 years.

Average lifespan

Status: wild: 1 years.

Adults mate within the first few days of emerging from the pupae. Little is known of the exact copulatory habits of the warble fly.

The life cycle of H. lineatum normally spans a year's time, with warbles forming most abundantly during March and April and adults normally appearing in April and May. The Hypoderma lineatum cycle tends shift one to two months earlier in southern climates.

Eggs are laid in rows of 5 or more (up to 16) on hairs, normally on the legs or lower abdomen of the host. One female may lay up to 800 eggs per host.

Key Reproductive Features: semelparous ; sexual ; fertilization (Internal ); oviparous ; sperm-storing ; delayed fertilization

After egg-laying there is no further parental care for the offspring of this species.

Parental Investment: pre-fertilization (Provisioning)

This species is in no danger of becoming extinct at this time.

US Federal List: no special status

CITES: no special status

Human cases of myiasis (infections by fly larvae) caused by H. lineatum larvae are rare; when found, the site of infection is normally the in neck region. Results of infection include leg paralysis (when spinal cord is affected), blindness (due to ocular myiasis), and creeping subcutaneous myiasis.

Hypoderma lineatum causes many problems for cattle which result in economic damage for humans. There are five major consequences that result from infection. At first, cattle experience severe weight loss due to the intense action of gadding, where the cattle gallop and run around wildly trying to escape the ovipositing females, which is believed to be stimulated by the buzzing of the flies. Secondly, because of the severe weight loss and the irritation due to the migrating larvae, milk production can be reduced up to 20 percent. Thirdly, as the larvae migrate through the host's tissue, the flesh contacted by the larvae becomes discolored, takes on a jelly-like appearance, and is no longer edible. The value of the cattle carcass is severely depreciated. Fourthly, the hide's value is also depreciated because of all the breathing holes made by the larvae. Lastly, warbles do not heal over, leaving the cattle susceptible to other infections and opening up opportunities for myiasis by other kinds of flies.

Negative Impacts: injures humans (causes disease in humans ); causes or carries domestic animal disease

It has no known positive effect.