Melanophora roralis

The combination of small size (under 6 mm), entirely black body, and darkened wings with white apical patches in females distinguishes this species from most other Diptera. The hairy antennae and shiny thorax are additional diagnostic features. In the field, association with woodlice or their habitats supports identification.

Small black fly measuring 3–5.5 mm in length. Antennae are hairy. Thorax is shiny. Wings are darkened; females possess a distinctive white patch at the wing tip. Body coloration is uniformly black.

Found in old forests, damp areas near shorelines, under bark, under stones, and among vegetation in upper seashore regions. Also occurs in anthropogenic settings including outhouses and gardens. Adults frequently rest on light-colored vertical surfaces such as walls or rocks.

Native to the Palaearctic region (excluding northernmost areas) and the Afrotropical region (Cape Verde). Introduced to the Nearctic region (Southern Ontario) and Neotropical region (Chile and Argentina). Present in Britain and Ireland, and on the Azorean islands of Faial, São Miguel, and Terceira. Also recorded from Denmark and Norway.

Adults are active from mid-May to October.

Larvae are obligatory parasitoids of woodlice and other terrestrial isopods, feeding internally and killing the host. Adults do not require a meal for ovarian maturation.

• Porcellio scaber - primary hostWell-documented natural host
• Cylisticus convexus - laboratory hostSuccessfully reared in captivity
• Porcellio dilatatus - laboratory hostSuccessfully reared in captivity
• Porcellionides floria - laboratory hostSuccessfully reared in captivity
• Porcellionides pruinosus - laboratory hostSuccessfully reared in captivity
• Oniscus asellus - hostRecorded as host
• Asopia farinalis - possible hostMoth larva; record from single source (Séguy 1941) with uncertain validity
• Larinioides cornutus - possible hostSpider egg-cocoons; record from older sources with less certainty

Eggs hatch after approximately 7 days. Larvae pass through three instars. The first instar larva attaches to a host and penetrates the intersegmental membrane of a recently moulted woodlouse. Internal feeding continues until the host is killed; the larva then pupates inside the host remains. Pupation may take up to 21 days.

First instar larvae rest on the posterior end perpendicular to the substrate. When disturbed, they extend anteriorly and move in circular or figure-of-eight motions while searching for a host. Locomotion includes somersaulting. Larvae attach to any moving object but only remain on suitable hosts. Females perform wing fluttering during oviposition. Mating occurs without pre-feeding: females are receptive within an hour of emergence, males usually after twelve hours. A mating dance involving wing fluttering is initiated by the female.

Acts as a parasitoid regulating populations of woodlice and other terrestrial isopods. May also target spider egg-cocoons and moth larvae, though these associations are less certain.

No significant direct impact on human health or agriculture. Presence in gardens and outhouses indicates adaptation to human-modified environments.

• Other RhinophoridaeShare general body plan and parasitoid lifestyle, but most lack the distinctive white wing-tip patches of female M. roralis and differ in host associations.
• Calliphoridae (sensu lato)Historically confused due to taxonomic reclassification; M. roralis was previously placed in Calliphoridae but differs in smaller size, darkened wings, and specialized woodlouse parasitoid ecology versus the generalist carrion-feeding habits of most blow flies.

Formerly classified in family Calliphoridae; modern taxonomy places it in Rhinophoridae based on morphological and molecular evidence.

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• The genome sequence of a woodlouse fly, Melanophora roralis (Linnaeus, 1758).