The cheese fly, cheese skipper, or ham skipper (''Piophila casei'') is a

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of fly from the family

Piophilidae The Piophilidae are a Family (biology), family of "true flies", in the Order (biology), order Diptera. The so-called cheese flies are the best-known members, but most species of the Piophilidae are scavengers in animal products, carrion, and fun ...

whose

larvae A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect developmental biology, development such as insects, some arachnids, amphibians, or cnidarians typical ...

are known to infest cured meats, smoked or salted fish, cheeses and

carrion Carrion (), also known as a carcass, is the decaying flesh of dead animals. Overview Carrion is an important food source for large carnivores and omnivores in most ecosystems. Examples of carrion-eaters (or scavengers) include crows, vultures ...

. On the

Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

island of

Sardinia Sardinia ( ; ; ) is the Mediterranean islands#By area, second-largest island in the Mediterranean Sea, after Sicily, and one of the Regions of Italy, twenty regions of Italy. It is located west of the Italian Peninsula, north of Tunisia an ...

, the larvae are intentionally introduced into pecorino sardo cheese to produce the characteristic '' casu martzu''. If consumed by humans, the larvae have a chance to survive in the

intestine The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...

, causing enteric

myiasis Myiasis ( ), also known as flystrike or fly strike, is the parasitic infestation of the body of a live animal by fly larvae (maggots) that grow inside the host while feeding on its Biological tissue, tissue. Although flies are most commonly attr ...

, though no such cases have been linked to ''casu martzu'' dishes. The larvae may also carry harmful microorganisms that, when consumed, could cause infections.

Description

Adult male cheese flies are usually long, with females slightly larger at long. The body is primarily a metallic black bronze in color, with two pale yellow

iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear gradually to change colour as the angle of view or the angle of illumination changes. Iridescence is caused by wave interference of light in microstruc ...

wings that lie flat upon the fly's

abdomen The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...

when at rest. The head has short antennae and red compound eyes, with yellow patches on the lower face. The legs are yellow-brown and are covered in short spines. The cheese fly

larva A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...

e are cylindrical and can appear white or cream, with black mouthparts.

Life history

Larvae have three instars, with late-instar larvae capable of greatest dispersal. When fully grown, they are long, wide, and have 13 segments. When disturbed, or dispersing to sites for

pupation A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...

, the larvae can leap by hooking their mouths into a nearby surface or into their own posterior segments, contracting their muscles, and releasing, flinging themselves forward—this locomotion technique is believed to be what has led to the name "cheese skippers". Larvae are

detritivores Detritivores (also known as detrivores, detritophages, detritus feeders or detritus eaters) are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal parts as well as feces). There are many kinds of invertebrates, ...

, feeding on protein rich sources, including meats, cheeses, and carrion. They seek out dark, dry areas for pupation, which lasts around 12 days. Adult larvae can overwinter before pupation. In cases of

, larvae that are embedded in unrefrigerated meats and cheeses can be ingested, then pupate and emerge as adults while still in the host's

alimentary tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascular system. T ...

Cheese flies and food safety

''P. casei'' are considered pests in the meat and cheese industries. Female cheese flies lay eggs on meats and cheeses, which, when hatched, produce burrowing larvae that are difficult to detect in food products until they grow large enough to disperse. Research conducted on methods for preventing the oviposition and larval infestation of ''P. casei'' in cured meats and cheeses suggests the use of certain plant essential oils, from plants such as '' Mentha canadensis'', to prevent larval growth. Alternatively, regulating the

microbiome A microbiome () is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupying a reasonably wel ...

present in food processing facilities can remove the microbial symbionts of ''P. casei'', whose metabolic wastes provide food for ''P. casei'' larvae.

References

External links

Image of ''Piophila casei''
Los Angeles County Natural History Museum Flies described in 1758 Piophilidae Taxa named by Carl Linnaeus {{Improve categories, date=March 2025