Epacmus
Osten Sacken, 1886
Species Guides
1Epacmus is a of bee flies ( Bombyliidae) characterized by a distinctive case of mimicry. possess four prominent, black, polished, hemispherical bumps on the rear of the that strikingly resemble the of jumping spiders (Salticidae). When viewed from behind, these structures create the illusion of a small salticid spider, potentially deterring . The genus is small-bodied, measuring approximately 7–10 mm in length, with a tapered, fuzzy appearance and delicate wings. Taxonomic validity remains debated, with some authorities considering Epacmus a synonym of Aphoebantus.
Pronunciation
How to pronounce Epacmus: /ɛˈpakməs/
These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.
Identification
Distinguished from other small bee flies by the four prominent black thoracic visible from a view. Similar in general form to Aphoebantus, from which it may not be separable without examination of the thoracic . The -mimicry structures are unique among North American Bombyliidae and serve as a field mark when the insect is observed from behind. Caution: some authorities synonymize Epacmus under Aphoebantus, making identification to level taxonomically contentious.
Appearance
Small bee flies, 7–10 mm in length, with a tapered, fuzzy body. view shows a dark smiley- pattern where the meets the . Most distinctive feature: four large, black, polished, hemispherical on the thorax, positioned to mimic jumping spider . Wings are delicate and membranous. present, with males and females distinguishable by subtle morphological differences.
Habitat
Open prairie and grassland . Observed on flowers and vegetation close to the ground. Vacant lots and undeveloped grasslands in urbanizing areas.
Distribution
Documented from Colorado Springs, Colorado, USA. Distribution otherwise poorly documented; likely occurs more broadly in western North American grasslands.
Behavior
visit flowers. When viewed from behind, the thoracic create a visual illusion of a jumping spider's , a putative case of mimicry (elusive mimicry). The adaptive value of this display has been hypothesized but not experimentally tested.
Ecological Role
likely serve as . The mimicry hypothesis, if correct, would represent a rare case of prey-to-predator mimicry in Diptera, potentially reducing pressure from jumping spiders.
Human Relevance
Of interest to entomologists studying mimicry systems and visual anti- defenses. Taxonomic status impacts nomenclatural stability in Bombyliidae.
Similar Taxa
- AphoebantusMay be congeneric; some authorities treat Epacmus as a synonym of Aphoebantus. Separation, if valid, relies on the distinctive thoracic of Epacmus.
- Ceratitis alba (Tephritidae)Shares convergent trait of raised thoracic features mimicking jumping spider , but belongs to a different (fruit flies rather than bee flies).
- Brenthia (metalmark moths)Convergent mimicry strategy: underside wing patterns mimic jumping spider and legs. Different taxonomic group (Lepidoptera) and different body region (wings vs. ) used for mimicry.
More Details
Taxonomic uncertainty
At least one world authority on Bombyliidae considers Epacmus potentially synonymous with Aphoebantus (Melander 1950; pers. comm. cited in source). The was described by Osten Sacken in 1886.
Predator mimicry context
The thoracic mimicry in Epacmus was first documented observationally in 2020 ( Eric blog). This follows formal recognition of similar mimicry in metalmark moths (Rota & Wagner 2006) and tephritid fruit flies (Mather & Roitberg 1987). The phenomenon—prey mimicking its predator—may be more widespread than currently recognized due to perceptual scaling differences between human and observers.
Co-occurring predators
Habronattus jumping spiders, abundant in prairie where Epacmus occurs, hunt on flowers and low vegetation—exactly where bee flies are active. One observation documented a jumping spider stalking a mining bee on the same flowers where Epacmus was photographed.