''Oestrus ovis'', the sheep bot fly, is a widespread species of

fly Flies are insects of the Order (biology), order Diptera, the name being derived from the Ancient Greek, Greek δι- ''di-'' "two", and πτερόν ''pteron'' "wing". Insects of this order use only a single pair of wings to fly, the hindwing ...

of the genus ''

Oestrus The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous ...

''. It is known for its parasitic predation and damage to

sheep Sheep or domestic sheep (''Ovis aries'') are domesticated, ruminant mammals typically kept as livestock. Although the term ''sheep'' can apply to other species in the genus ''Ovis'', in everyday usage it almost always refers to domesticated s ...

deer Deer or true deer are hoofed ruminant mammals forming the family Cervidae. The two main groups of deer are the Cervinae, including the muntjac, the elk (wapiti), the red deer, and the fallow deer; and the Capreolinae, including the reindeer ...

goats The goat or domestic goat (''Capra hircus'') is a domesticated species of Caprinae, goat-antelope typically kept as livestock. It was domesticated from the wild goat (''C. aegagrus'') of Southwest Asia and Eastern Europe. The goat is a membe ...

and sometimes

cattle Cattle (''Bos taurus'') are large, domesticated, cloven-hooved, herbivores. They are a prominent modern member of the subfamily Bovinae and the most widespread species of the genus ''Bos''. Adult females are referred to as cows and adult mal ...

. There have also been many records of

horse The horse (''Equus ferus caballus'') is a domesticated, one-toed, hoofed mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million y ...

dog The dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated descendant of the wolf. Also called the domestic dog, it is derived from the extinct Pleistocene wolf, and the modern wolf is the dog's nearest living relative. Do ...

and human infestation. In some areas of the world it is a significant pest which affects the agricultural economy.

Description

The adult fly is a bee-sized insect about 10 to 12 millimetres (3/8–½ inches) long, slightly hairy with a banded, dark grey body and dull yellow head and legs. It is widely distributed across the world wherever sheep, deer and goats are found. This includes

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

Central America Central America ( es, América Central or ) is a subregion of the Americas. Its boundaries are defined as bordering the United States to the north, Colombia to the south, the Caribbean Sea to the east, and the Pacific Ocean to the west. ...

, the area round the

Mediterranean Sea The Mediterranean Sea is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean Basin and almost completely enclosed by land: on the north by Western and Southern Europe and Anatolia, on the south by North Africa, and on the ea ...

The Middle East The Middle East ( ar, الشرق الأوسط, ISO 233: ) is a geopolitical region commonly encompassing Arabia (including the Arabian Peninsula and Bahrain), Asia Minor (Asian part of Turkey except Hatay Province), East Thrace (Europea ...

Australia Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...

Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...

and

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...

. Incidence of the fly in northern Europe has decreased in recent years.

Life cycle

Sheep bot flies commence life as eggs within the female which are fertilised and hatch to

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e of 1 mm within the body of the female. The female then deposits a few larvae, while on the wing, within a tiny mucous drop, directly into a nostril of the host animal. The larvae then make their way up the nasal passage in the mucosa and enter a

nasal sinus Paranasal sinuses are a group of four paired air-filled spaces that surround the nasal cavity. The maxillary sinuses are located under the eyes; the frontal sinuses are above the eyes; the ethmoidal sinuses are between the eyes and the sphenoid ...

. During this time it will develop, grow and moult into a second larval stage or instar. It then continues to develop up to 20mm (approximately 4/5 inch) in length with a dark stripe across each segment. When the larva is fully developed it moves down the nasal passage and drops to the ground where it buries itself and pupates. The length of time the larva takes to mature depends on the ambient temperature. This may be 25–35 days in warm weather but up to 10 months in colder climates. The pupa takes from 3–9 weeks to mature, again dependent on climatic conditions, after which the adult burrows up to the surface, takes to the wing and commences mating. The adults do not feed during their 2–4 weeks of adult life though they may take water.

Effects on livestock

Sheep are the principal hosts. The presence of the fly with its distinctive buzzing can alert mature animals who may attempt to run away, walk with their noses near the ground or have been recorded forming a circle with their noses in the middle and near the ground. If the fly successfully places eggs in the

nostril A nostril (or naris , plural ''nares'' ) is either of the two orifices of the nose. They enable the entry and exit of air and other gasses through the nasal cavities. In birds and mammals, they contain branched bones or cartilages called turbi ...

of sheep the animal may feel the larvae after a few days and attempt to remove them by tapping their muzzles on the ground. They will also snort and stamp their front feet in annoyance. Once the larvae have infested the nasal passage and sinuses, usually up to 15 larvae but can be up to 80, they cause irritation to the mucosa, which causes mucous discharge, swelling of the internal membranes of the nose, possibly impairment of breathing but largely discomfort and distraction to the sheep who may reduce or stop grazing and subsequently lose weight and condition. This can in some cases lead to malnutrition and death Sometimes mature larvae are unable to escape from the nasal sinus and die. This may then lead to a septic sinusitis affecting the animal's condition. and the possibility of death from general septicaemia.

Control of infestation

In developed countries sheep and other domestic animals can be given preventative medication in the form of drenches. These have a variable effect because reinfestation from neighbouring territory is common. In isolated flocks of animals control can be more effective.

Human infestation

There have been widespread reports of human infestation going back over decades, and probably centuries. Most commonly they are shepherds living in close proximity to the sheep but there are records of hapless visitors being subject to infestation and carrying the parasites home to their native country. The effects can usually be treated easily with medical attention or medication.

References

External links

Slideshow of Myiasis
{{Taxonbar, from=Q2213119 Veterinary entomology Oestridae Parasitic flies Parasitic arthropods of mammals Flies described in 1758 Taxa named by Carl Linnaeus