Acroceridae

small-headed flies, hunch-back flies, spider flies

Genus Guides

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Acroceridae are a small of approximately 520 in 50 , characterized by their distinctive hump-backed and disproportionately small . are primarily nectar feeders with exceptionally long , while larvae are obligate endoparasitoids of spiders. Many species exhibit or mimicry. The family is but nowhere abundant, with most species known from fewer than 10 specimens.

Pterodontia westwoodi by (c) Hila Taylor, some rights reserved (CC BY), uploaded by Hila Taylor. Used under a CC-BY license.Eulonchus sapphirinus by no rights reserved, uploaded by Jesse Rorabaugh. Used under a CC0 license.Eulonchus sapphirinus by no rights reserved, uploaded by Jesse Rorabaugh. Used under a CC0 license.

Pronunciation

How to pronounce Acroceridae: /æˌkroʊˈsɛrɪdaɪ/

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

Identification

Distinguished from similar by combination of: hump-backed with small ; in both sexes (unusual among Diptera); large squamae covering ; long carried beneath body rather than projecting forward; and globular . Resembles Bombyliidae and Nemestrinidae in general form but differs in head structure and proboscis carriage. mimics may be confused with actual Hymenoptera but lack constricted waist and have single pair of wings.

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Habitat

Most commonly encountered in semiarid tropical locations. often found on flowers, particularly in July and August in Palearctic region. Larvae occur wherever spiders are present. Appear episodically; rarely observed in most locations despite distribution.

Distribution

in distribution but nowhere abundant. Documented from all major biogeographic regions including Palearctic, Nearctic, Neotropical, Afrotropical, Oriental, and Australasian realms. Specific records include Chile (33 ), Brazilian Atlantic Forest, and Schleswig-Holstein (Germany).

Seasonality

most commonly observed in July and August in . Activity patterns elsewhere poorly documented due to rarity of encounters.

Diet

feed on floral nectar using exceptionally long . Some are specialized , showing high floral constancy and effective pollen transport.

Host Associations

Life Cycle

Hypermetamorphic development. Females lay up to 5,000 on ground or vegetation. First-instar larvae () actively seek spider using looping movement or leaping several millimetres into air. Upon contact, planidium crawls up spider's legs, penetrates body wall at , and lodges near book lung where it may remain in for months to years. Subsequent larval instars develop rapidly, consuming host's liquid contents. Mature larva emerges posteriorly from host, attaches to spider silk for . emerge in 7–10 days.

Behavior

do not seek ; host location is entirely larval responsibility. When feeding, adults extend to access nectar; when not feeding, proboscis is concealed lengthwise beneath body. Mating occurs within flower patches in at least some . Females visit more individual flowers and forage more slowly than males, apparently related to mating .

Ecological Role

As of spiders, regulate spider . function as in some , with Eulonchus sapphirinus documented as visitor to Geranium robertianum flowers in Olympic National Park. Compete with certain for endoparasitic in spiders.

Human Relevance

Occasionally encountered by arachnologists when field-collected spiders produce flies in captivity. Some used in research. Subject of recent phylogenomic research due to uncertain placement within Diptera tree of life.

Similar Taxa

  • BombyliidaeSimilar -mimic appearance and long , but Acroceridae have in both sexes, hump-backed , and carry proboscis beneath body rather than projecting forward.
  • NemestrinidaeRelated with similar nectar-feeding habits and hypermetamorphic larvae, but Acroceridae distinguished by small , hump-backed profile, and spider-specific .

More Details

Taxonomic uncertainty

Placement within Diptera remains unresolved; studies suggest closest relationship to Nemestrinidae and Bombyliidae, while morphological analyses indicate possible sister group relationship to Asiloidea and . Phylogenomic analyses yield conflicting topologies depending on versus coding.

Rarity in collections

Of more than 500 described , most are known from fewer than 10 specimens, making this one of the most poorly represented dipteran in entomological collections despite distribution.

Classification history

2019 revision based on phylogenetic studies recognized five extant and one extinct subfamily containing Archocyrtus from Late Jurassic Karabastau Formation of Kazakhstan.

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Sources and further reading