Therevidae

Stiletto flies

Subfamily Guides

Therevidae, commonly known as stiletto flies, is a of brachyceran flies in the superfamily Asiloidea containing approximately 1,600 described worldwide. The family is most diverse in arid and semiarid regions with sandy soils. are small to medium-sized (2.4–18 mm) with hairy bodies and are often brightly colored, with many species exhibiting or mimicry. Larvae are apodous, eucephalic, and predatory, living in soil and other substrates where they hunt insect larvae.

Thereva by (c) Michael Knapp, some rights reserved (CC BY), uploaded by Michael Knapp. Used under a CC-BY license.

Chromolepida bella by (c) Don Loarie, some rights reserved (CC BY), uploaded by Don Loarie. Used under a CC-BY license.

Nebritus tanneri by (c) Rebecca Ray, some rights reserved (CC BY), uploaded by Rebecca Ray. Used under a CC-BY license.

Pronunciation

How to pronounce Therevidae: /ˈθɛrəvɪdiː/

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

Distinguished from the related Asilidae (robber flies) by: (1) ending in two fleshy for sucking liquids rather than a piercing predatory structure; (2) presence of fluffy setae above mouthparts that are not stiff protective bristles () like the mystax of Asilidae; (3) less obvious depression on the vertex between the . Wing venation lacks distinctive family-specific conformation but shows characteristic branching patterns: R 2+3 undivided, R 4 long and winding to costal margin, R 5 to border leaving second submarginal open at wing apex. Male terminalia and female genitalia characters are critical for generic and -level identification; non-genitalic characters can identify in some regional faunas.

Images

Appearance

are small- to medium-sized flies with body length ranging from 2.4 to 18 mm. The is hairy, with coloration varying from yellow to black, though background color is often masked by tomentum. Males typically have larger than females; in many males are ( contiguous at vertex), while females are dichoptic (eyes separated). Three ocelli are present. are relatively short with an elongated scape, very short , and a conical, elongated first flagellomere bearing a compound stylus with one to three segments. The terminates in two fleshy adapted for sucking liquid foods, not a piercing predatory organ. The is broad and moderately convex with long bristles (macrotrichae). Legs are long and slender with bristles on and tibiae; tibiae lack spurs. Wings are well developed, hyaline or opaque, often with pigmented at terminations of transverse and longitudinal veins. The is tapered and elongated, typically 3–4 times longer than its broadest width when not extended. Eight abdominal segments are externally visible. Wing venation is complex: divided into four branches with R 2+3 undivided; R 4 long and winding, reaching costal margin; R 5 terminating on border; media divided into four independent branches with M 3 and M 4 convergent; elongated, terminating at apex with three angles. Larvae are apodous (legless), eucephalic, cylindrical, very long and thin with tapered ends; integument smooth, white or pink; capsule well developed but narrower than other body regions.

Habitat

occur in diverse environments including streams, meadows, open woodlands, dry and sandy places, and beaches. Preferred are those that suit larval development: thickets of xerophilous plants (garrigue and maquis), deserts, and sandy beaches. Larvae inhabit dry, sandy soils, dry litter, decomposing organic matter, and under tree bark. The shows greater breadth than other Asiloidea.

Distribution

, represented in all zoogeographical regions. Most diverse in arid and semiarid regions with sandy soils. The Therevinae occurs on all continents with lower frequency in eastern regions; Phycinae in Afrotropical and Holarctic regions; Xestomyzinae mainly Afrotropical; Agapophytinae to Australasian realm. In Europe, only Phycinae (two ) and Therevinae (15 genera) are present, with 98 reported, two-thirds belonging to genus Thereva.

Seasonality

Generally with short, quick . Flight period varies by and region; in British Columbia, Yukon, and Alaska, specific flight periods are documented for regional species. are particularly attracted to water and moisture sources, often remaining near pools or other sources of moisture even in semiarid regions.

Diet

feed primarily on nectar, honeydew, and pollen; occasionally on liquid secretions of animal or vegetable origin. Larvae are entomophagous of insect larvae and pupae in soil, including prey from Diptera, Coleoptera, and Lepidoptera.

Life Cycle

Lifecycle typically completed in one per year, though some European have cycles of two or more years. stage is the mature larva. Postembryonic development includes five instars; occurs in spring.

Behavior

are generally and move in short, quick . At rest, substrate choice varies by : some rest on ground, others on rocks, vegetation, or intertidal debris. Adults are strongly attracted to water sources. Larvae exhibit voracious feeding and agile movements; when exposed to light, they rapidly dig back into substrate. Larvae use vibrations to locate prey while moving through loose sand. Many species exhibit or mimicry in coloration and .

Ecological Role

Larvae function as of soil-dwelling insect larvae, potentially regulating of other insects in sandy and arid . may contribute to pollination through nectar and pollen feeding. The represents a component of predator-prey dynamics in xerophilous and sandy .

Human Relevance

Of limited direct economic importance. Some have been studied for potential, particularly in Australia where research on stiletto flies has been active. The has been subject to extensive taxonomic revision due to historical confusion with related families. Biolegacy programs have used undescribed Therevidae species for species-naming sponsorships to support museum research.

Similar Taxa

AsilidaeSimilar superfamily Asiloidea; distinguished by piercing predatory , stiff mystax bristles, and more obvious vertex depression between .
ScenopinidaeRelated in Asiloidea; Therevidae distinguished by wing venation patterns and genitalic characters.
MydidaeAnother asiloid ; Therevidae separated by structure, wing venation, and larval .