October Caddis
Dicosmoecus
Key Identification Characters - Larva: 2
- Large cased caddis. Case of mature larva made of fine gravel with little taper from front to back. Case of young immature larvae often made largely of plant material
- Head and legs almost black in color, body cream to pale yellow.
- Length of case up to 36mm.
Similar larvae: 2
The family Limnephilidae contains some 39 genera and over 300 species in North America. The genus Dicosmoecus occurs only in western North America and stands out for its size and large, robust, almost straight sided case of the mature larvae.
Key Identification Characters - Adults: 2
- Distinctive pale orange to yellow-orange body and legs. Eyes and antennae dark reddish-brown to black.
- Wings light to dark gray with very distinct dark venation.
- Large: Length from head to tip of wings up to 35mm.
Similar adults: 2
The large size, yellow-orange color, and fall emergence make identification of the October caddis fairly easy. However, there are five species of Dicosmoecus known to occur in western streams (four in Oregon). D. gilvipes and D. atripes are the two most common and abundant with D. gilvipes the most widespread of the two. To clearly document the species present, specimens should be collected (preferably males) and sent to a taxonomist.
Habitat & Distribution: 2
Dicosmoecus live throughout the West with excellent populations found west of the continental divide. They inhabit a wide range of streams, from large rivers to smaller headwater streams. Larvae prefer moderate to fast water with a large boulder substrate. In late spring and early summer the large larvae can be seen meandering over the tops of boulders grazing on diatoms and algae like slow moving cows.
In Oregon it is a rare stream or river that doesn’t have at least some Dicosmoecus. On many of the larger rivers like the Deschutes, Sandy, Clackamas, Molalla, McKenzie, Rogue, and others, they are the most obvious caddis observed in the fall months.
Life Cycle - Emergence: 2
Throughout its range Dicosmoecus is primarily a fall emerger, which accounts for its two common names: October caddis or fall caddis. While considered a fall emerger, depending the stream adults may be seen from July through October. Also depending on location both one-year and two-year life cycles have been documented.
In Oregon most October caddis emerge from mid-September through October, but adults can be collected as early as July in some locations.
Oregon Emergence Period: mid September through October
Metolius: July-September (flight period on the Metolius is much earlier than other Oregon streams).
McKenzie: mid September - late October.
Necanicum/Nehalem: August-October?
Sources and Credits
- (c) Jerry Schoen, all rights reserved, uploaded by Jerry Schoen
- (c) Jerry Schoen, some rights reserved (CC BY-SA)
