Small-headed Flies

Acroceridae

Classification

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.

Images

Unidentified sp. by the Smithsonian. Used under a CC0 license.
Unidentified sp. by the Smithsonian. Used under a CC0 license.
Unidentified sp. by the Smithsonian. Used under a CC0 license.
Unidentified sp. by the Smithsonian. Used under a CC0 license.
Psilodera confusa by the Smithsonian. Used under a CC0 license.
Psilodera confusa by the Smithsonian. Used under a CC0 license.

Summary

The Acroceridae, known as small-headed flies or spider flies, are a unique and small family of flies characterized by their hump-backed appearance and small heads. They are parasitoids of spiders and exhibit a hypermetamorphic lifecycle, which influences their ecological role.

Physical Characteristics

Small to fairly large flies with a wingspan over 25 mm in some species; hump-backed appearance with a small head; long proboscis for accessing nectar; compact body without major bristles; many species exhibit bee-like hairiness and mimic bees or wasps. Holoptic eyes in both sexes and disproportionately large squamae that completely cover the halteres.

Identification Tips

For genera identification, observe the number of ocelli and abdominal shape. Eulonchus has 3 ocelli on a tubercle, while Lasia has 2 ocelli and a more swollen abdomen. Ocnaea has distinctive antennae nearly as long as the face; Turbopsebius has densely pilose eyes. Acrocera has very short antennae inserted near the bottom of the eyes.

Habitat

Commonly found in semi-arid tropical locations; cosmopolitan distribution but rarely abundant. They predominantly inhabit areas where host spiders are present since they are parasitoids.

Distribution

Cosmopolitan, most diverse in the southwestern United States. Generally rare and not widely observed, with many species known from fewer than 10 specimens.

Diet

Adults are nectar feeders, utilizing exceptionally long proboscises to access nectar, while larvae are parasitoids of spiders.

Life Cycle

Undergo hypermetamorphosis, with larvae (planidia) that seek out spiders as hosts. The planidia grab hold of a spider and enter its body, often residing there for years before pupation.

Reproduction

Females lay a large number of eggs, potentially up to 5,000, with the first-instar larva (planidium) seeking out spider hosts.

Ecosystem Role

As parasitoids of spiders, they play a role in the control of spider populations and contribute to the food web dynamics of their ecosystems.

Collecting Methods

  • Collect spiders from the field and observe for the presence of planidia.
  • Nectar feeding adults can be observed on flowers during their active months.

Preservation Methods

  • Standard entomological techniques for pinning and preserving specimens in ethanol or isopropyl alcohol.

Evolution

Part of the infraorder Muscomorpha; molecular data suggests a close relationship with families Nemestrinidae and Bombyliidae. Revised classification in 2019 proposed five extant subfamilies.

Similar Taxa

Misconceptions

Due to their appearance and behavior, they are sometimes confused with other dipteran families, particularly those that are bee or wasp mimics.

Tags

  • Diptera
  • Acroceridae
  • Small-headed Flies
  • Spider Parasitoids
  • Entomology