Black Drake
Siphlonurus occidentalis
Key Identification Characters - nymph 2
- Mature nymph ~15mm long (excluding tails).
- Antennae short - less than 2 times head width.
- Gill plates large, with double plates on abdominal segments 1 & 2.
- Three tails equal length, fringed with fine hairs.
- Body color generally brown to gray.
Similar nymphs: 2
Mayfly nymphs most easily confused with Siphlonurus are Callibaetis or Speckle-winged Quill nymphs. The two can be easily distinguished by the length of their antennae: Callibaetis antennae are 2 - 4 times the width of the head in length, Siphlonurus less than twice the width of the head.
Key Identification Characters - adult 2
- Two tails.
- Hind wings with rounded costal angulation (slight hump along leading edge near base).
- Spinner color typically dark wine-red on back with lighter belly. Duns generally dark gray on top and light gray underneath.
- Male spinners with large eyes that may meet on top of the head and often with a pale band across middle of eyes.
- Body length 10 - 20mm.
Similar Winged Mayflies: 2
Possible confusing adult mayflies include Callibaetis and perhaps Rhithrogena (March Brown) spinners. Callibaetis can be separated by their small hind wings compared to the well-developed hind wings of Siphlonurus. Rhithrogena spinners are slightly smaller and live in fast-water habitat rather than the slow-water preference of Siphlonurus.
Habitat & Distribution 2
Siphlonurus nymphs live in both lakes and streams. In streams they live in water with little or no current. Nymphs are often collected in off-channel side pools left behind after high spring flows (see photo above). The nymphs are excellent swimmers and dart like little minnows when placed in a shallow tray of water.
The distribution of Siphlonurus is spotty. In Oregon the best populations occur in the slow meandering spring-creek like streams of south-central Oregon with exceptional numbers found in the Sprague and upper Williamson Rivers. Besides Siphlonurus occidentalis two other less common species, S. columbianus and S. spectabilis, also occur in the Northwest. Male spinners should be collected whenever possible to confirm species identification.
Life Cycle - Emergence 2
When ready to emerge, nymphs crawl from the water up streamside grasses or other nearby vegetation, though there is some speculation that emergence may also occur on the water’s surface. Dun emergence is generally thought to occur either at night or just after sunset or before sunrise. Spinner falls tend to be dense and can occur any time between mid morning and late evening depending on weather and air temperature. Due to emergence behavior duns are rarely seen or collected, while spinners occur in dense concentrations.
Emergence in south-central Oregon streams tends to begin as early as late May and last until early July, with peak hatches often in early to mid June. Hatches start earlier at lower elevation reaches of streams. In other regions of the West, like the Rocky Mountains and British Columbia, Siphlonurus emergence may range from early August to mid September.
Metolius: Not present McKenzie: Not present Necanicum/Nehalem: Not present.
Oregon Emergence Period: End of May to early July with peak activity often early to mid June.
Sources and Credits
- (c) Jerry Schoen, all rights reserved, uploaded by Jerry Schoen
- (c) Jerry Schoen, some rights reserved (CC BY-SA)
