Blera humeralis

Distinguished from other Blera species and similar syrphid flies by the combination of: opaque yellow postpronotum (humeri); large yellow mesopleural spot; specific abdominal pattern with finger-like yellow stripes that do not meet medially; and yellow legs with characteristic black and brown markings. The yellow stigma and predominantly yellow wing veins at the base and anterior margin are additional diagnostic features. The rat-tailed larval morphology separates it from non-eristaline syrphids.

Adults exhibit striking black and yellow patterning. The thorax is shining black with orange-yellowish pile and four more or less distinct cupreous stripes (vittae). The postpronotum (humeri) is opaque yellow. The scutellum is shining black with a yellow margin. A large yellow spot extends on the mesopleuron from the transverse suture to the middle legs. The abdomen is black with wide yellow finger-like stripes that do not meet medially, leaving a black central stripe. The second abdominal segment has a large triangular yellow spot rounded toward the mid-back; the third segment has a more rectangular yellow stripe. Sexual dimorphism occurs in abdominal banding: females have more broadly separated yellow bands on the third and fourth segments than males. The fifth segment is yellow with a black tip. Abdominal pile is fulvous (dull orange) and long on basal angles, black on the apical half of the second and third segments. Wings are cinereous (ashy grey) hyaline, somewhat clouded on the outer part, with yellow stigma and yellow veins at the base and anterior margin. The squamae (calypters) are whitish with yellow border and pale yellow fringe. Halteres are yellow.

Associated with woodland environments, particularly where trees produce sap flows or develop rot holes. Larval habitat consists of exuding sap and rot holes in trees. Adult habitat includes flowering vegetation in or near wooded areas.

Nearctic region, distributed along the coast of western North America. Specific documented locations include coastal areas from California northward, though precise range boundaries require further documentation.

Adults feed on nectar and pollen from flowers. Larvae feed on exuding tree sap or in rot holes of trees.

Larvae are of the rat-tailed type, possessing a telescoping posterior respiratory siphon that allows breathing while submerged in liquid substrates. Development occurs in exuding sap or rot holes of trees. Specific details of egg laying, pupation, and adult emergence are not documented in available sources.

Adults are flower visitors. Like other hoverflies, they are capable of nearly motionless hovering flight. The species is considered uncommon, suggesting either genuinely low population densities or habits that make it infrequently encountered.

Adults contribute to pollination through flower visitation. Larvae function as saprophages in tree rot holes and sap flows, contributing to nutrient cycling in woodland ecosystems.

No documented economic or medical significance. The species is of interest to entomologists and naturalists due to its distinctive appearance and uncommon status. Not known to be a pest or beneficial species in agriculture or forestry.

• Blera fallaxAnother Blera species with similar woodland habitat and rat-tailed larvae; distinguished by specific color pattern differences, particularly in thoracic and abdominal markings.
• Other Milesiini genera (e.g., Criorrhina, Spilomyia)Share rat-tailed larval type and similar adult habits; distinguished by specific thoracic and abdominal color patterns, leg coloration, and wing venation details.

• Syrphidae
• hoverfly
• wood fly
• Nearctic
• sap-feeding larvae
• pollinator

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
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