Wohlfahrtia magnifica, the spotted flesh fly, is a Dipteran fly whose larvae attack mainly sheep and goats, sometimes also cattle, horses, camels and other mammals, occasionally humans and poultry as well. Usually it does not affect dogs and cats.

Wohlfahrtia magnifica occurs around the Mediterranean, in Russia and in China. Regional abundance depends strongly on climatic and ecologic conditions, but also on the susceptibility of individual sheep and goat breeds. High incidence has been reported e.g. in Greece (up to 80% of sheep affected), Russia (30% - 50% of sheep affected), Hungary (5% - 39% of sheep affected), etc.

Other Wohlfahrtia species affect various mammals but are not relevant for livestock, and only occasionally important for pets, e.g.

• Wohlfahrtia vigil, the gray flesh fly; affects foxes, rabbits and occasionally dogs and cats.
• Wohlfahrtia meigeni, affects foxes and minks.
• Wohlfahrtia nuba, affects camels.

Wohlfahrtia flies are obligate parasites, i.e. they cannot complete their life cycle on alternative substrates such as carrion or dung. 

Biology and life cycle of Wohlfahrtia magnifica

Adult flies have a dark color and reach about 10 mm length. The life cycle needs 4 to 6 weeks to be completed. Adult females are larviparous, i.e. they do not deposit eggs, but larvae that have already hatched inside the uterus before deposition. One female lays about 150 larvae in her lifetime, preferentially in the genitalia of the hosts, but also on open wounds and mucosae, e.g. in the mouth, nose, ears or eyes.

Larvae feed for 4 to 8 days on the host's superficial tissues, which are progressively destroyed. Feeding larvae burrow deeply in the hosts flesh and may not be noticed when superficially examining the wounds. Mature larvae are up to 20 mm long. They drop to the ground for pupation. Adults emerge 4 to 12 days later.

In most endemic regions it is a seasonal pest with highest incidence during the summer months.

Click here to learn more about the general biology of insects.

Harm and economic loss due to Wohlfahrtia magnifica

As for most cutaneous myiasis, annoyance for affected animals is substantial. The wounds caused by the maggots become necrotic and hemorrhagic, often infected with secondary bacteria. Animals are progressively weakened and if left untreated fatalities are not rare.

Incidence and subsequent economic impact in a particular region varies considerably. For reasons not yet completely understood there are years with a very low incidence, and years with massive outbreaks.

Prevention and control of Wohlfahrtia magnifica

An important preventative measure in endemic regions is to avoid handling practices that cause injuries to sheep and other livestock during the peaks in the fly season. This includes parturition, castration, dehorning, shearing, tail docking, etc. that attract egg laying flies to the resulting injuries.

Preventing infestations with blood sucking parasites (e.g. ticks, horn flies, stable flies, horse and deer flies, etc.) will also reduce the incidence cutaneous myiasis, because Wohlfahrtia flies are also attracted to such minute wounds as those caused by these parasites.

The longest preventative effect so far has been reported for the insect development inhibitor dicyclanil administered as a pour-on to sheep. 100% protection for 24 weeks and >80% protection for 31 weeks have been reported after a single treatment. There are also reports on several weeks protection achieved after a single treatment with cyromazine, another insect development inhibitor.

Many concentrates used for periodically dipping or spraying livestock against ticks and flies will usually kill established Wohlfahrtia infestations as well, but only those that contain synthetic pyrethroids (e.g. cypermethrin, deltamethrin, permethrin, etc.) and organophosphates (e.g. chlorpyrifos, chlorfenvinphos, coumaphos, etc.), not those with amitraz. However, protection against re-infestation will last only for a few days. They are often used to treat sheep flocks after shearing for protection against Wohlfahrtia.  Pour-ons (backliners) with such parasiticides are often not suitable because they do not ensure complete coverage of the host's body.

Otherwise numerous ready-to-use dressings for direct treatment of maggots in injuries are available in most countries. They are used preventively for topical treatment of injured body parts after castration, dehorning, shearing, etc., as well as curatively for killing maggots already established in whatever injuries that animals can get. Such dressings are available in various formulations such as powders, lotions, ointments, creams, sprays, aerosols, etc. They contain larvicides belonging to the synthetic pyrethroids (e.g. cypermethrin, deltamethrin, permethrin), carbamates (e.g. carbaryl, propoxur) and organophosphates (e.g. chlorpyrifos, diazinon, trichlorfon, etc.). These dressings often contain disinfectants, painkillers, and/or wound healing chemicals as well. Such dressings for livestock are sometimes approved for use on dogs and cats as well.

Most systemic macrocyclic lactones (e.g. ivermectin, moxidectin) injected at the usual dose of 0.2 mg/kg are ineffective against Wohlfahrtia, both to cure established myiases and to prevent them. In a few investigations doramectin protected against infestation for periods of 1 to 3 weeks.

Insecticide-impregnated ear-tags (for cattle) are not adequate for protecting against Wohlfahrtia flies.

So far there are no effective repellents to keep Wohlfahrtia flies away from livestock or pets.

So far there are no effective biological control methods against Wohlfahrtia flies. Learn more about biological control of flies and other insects.

Resistance of Wohlfahrtia magnifica to parasiticides

So far there are no reports on resistance of Wohlfahrtia magnifica to parasiticides.

This means that if a particular product has not achieved the expected control, it is most likely because the product is not adequate or it was not used correctly, not because Wohlfahrtia magnifica populations have become resistant. Incorrect use is the most frequent cause of product failure.

Learn more about parasite resistance and how it develops.