The Delhi Sands flower-loving fly (Rhaphiomidas terminatus abdominalis) is named for the very specific habitat it requires - Delhi series sands occurring only on the Delhi Sands formation in southwestern California, an area of ancient inland dunes. This sand type currently exists only in San Bernardino and Riverside counties in southern California.

At 2.5 cm long, the Delhi Sands flower-loving fly is one of the largest flies in the world. It is orange-brown and black with dark brown oval spots.

Currently 12 populations exist and this species is the only fly on the Endangered Species List. It was federally listed in 1993. Ninety-seven per cent of this species' habitat has been destroyed. Development, agricultural conversion, sand mining, invasion by exotic species, dumping of cow manure and trash, and off-road vehicles continue to threaten the species.

endemic to a single state or province

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (<100-250 square km (less than about 40-100 square miles)) Currently occurs in southwestern San Bernardino and northwestern Riverside counties in California, an eight mile radius, but is presumed to have once occurred throughout the Colton Dunes, a 40 square mile area (USFWS, 1993).

Historic Range:
U.S.A. (CA)

Length: 2.5 cm

Comments: Found in "...fine, sandy soils, often with wholly or partly consolidated dunes". (USFWS, 1993). Restricted to a particular soil type classified as the 'Dehli' series.

Non-Migrant: No. All populations of this species make significant seasonal migrations.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 1 - 5

Comments: Five populations known to exist (USFWS, 1993).

Very little is known about the biology of this fly. Adults are active for a few weeks during August and September. A female lays up to 40 eggs in the sand and larvae hatch 11 to 12 days later. The larvae develop entirely below ground - this stage is believed to last for two years before adults emerge.

United States

Rounded National Status Rank: N1 - Critically Imperiled

Rounded Global Status Rank: T1 - Critically Imperiled

Reasons: Range has been dramatically reduced to a handful of sites that continue to be threatened by local development.

Current Listing Status Summary

Status: Endangered
Date Listed: 09/23/1993
Lead Region:   California/Nevada Region (Region 8) 
Where Listed:


Population detail:

Population location: entire
Listing status: E

For most current information and documents related to the conservation status and management of Rhaphiomidas terminatus abdominalis , see its USFWS Species Profile

Global Short Term Trend: Decline of 50-70%

Comments: Range has been reduced by over 97% (USFWS, 1993). Most of the former habitat was destroyed by conversion to agriculture in the area (USFWS, 1993).

Degree of Threat: A : Very threatened throughout its range communities directly exploited or their composition and structure irreversibly threatened by man-made forces, including exotic species

Comments: Threatened by construction of new homes, businesses, and roads. Small population size also leaves this species susceptible to loss of genetic variability (USFWS, 1993).

Global Protection: None. No occurrences appropriately protected and managed

Comments: All occurrences are on privately owned land.

Although not much is known about its biology, the fly is a known nectar feeder that hovers like a hummingbird as it feeds and flies quickly between flowers. It uses its long proboscis (a hollow straw-like organ) to suck nectar from flowers, and has been seen hovering over many native wildflowers in its habitat. However, the only flower the fly has been documented to nectar from is common buckwheat (Ermogonum fasciculatum), although other plants like California croton (Croton californicus) and telegraphweed (Heterotheca grandiflora) are also flowering during adult flying times and are potential nectar sources for the fly. Placement of the Delhi Sands flower-loving fly on the Endangered Species List has helped stop development projects in the remaining Delhi Sands habitat, a unique ecosystem which is home to other species with limited distribution, including the legless lizard (Anniella pulchra), San Diego horned lizard (Phrynosoma coronatum blainvillii), Delhi Sands metalmark butterfly (Apodemia mormo new subspecies), Delhi Sands Jerusalem cricket (Stenopelmatus new species), convergent apiocerid fly (Apiocera convergens), and the Delhi Sands sandroach (Arenivaga new species).