Sialis species


Identification: All Alderflies in Canada are Sialis  species. The bodies and wings are dark brown to blackish. They do not have simple eyes (ocelli) on the top of their head. Sometimes the head has orange spots. The neck is as wide as the head. The thorax is raised or humped. Feet are bi-lobed (two toes, projecting in opposite directions). Wings are held tent-like over the abdomen and are twice as long as the body. Males are smaller than females. 

Similar Species: Dobsonflies and Fishflies are twice as long (usually over 30 mm.) and their wings are held flat against their bodies, not tent-like.

Size: 9 to 15 mm.

Flight Time: May and June.

Habitat: Larvae live in mud-bottomed streams, rivers and ponds. Adults are weak flyers and seldom stray from water.

Food: Larvae feed on smaller aquatic animals.

Life Cycle: Adults mate at night, signalling to each other by abdominal vibrations. Adults may drink water or nectar, but usually do not feed and live only about 2 weeks. Females lay 200 to 500 eggs in a single layer on leaves, twigs and solid structures like the underside of bridges. Eggs are laid in rows, the female moving backward to deposit next row. Larvae hatch at night in 8 to 10 days and drop into the water, burrowing into the mud. Larvae may exude a black fluid from their mouth as a defence mechanism. The nymphs are 20 to 30 mm long (not including tail) and have 7 pairs of gills (filaments) on the abdomen sides and a long tail at abdomen tip. (Dobson and Fishfly larvae don’t have long tails, the Dobsonfly Corydalus cornutus larvae have two small tails at abdomen tip.) It usually takes more than one year, sometimes 2 to 3 years to complete larval development with 10 instars. To pupate, larvae crawl out of the water and find a damp place in soil, usually under rocks or logs, but do not form cocoons; hatching in about 2 to 3 weeks. Recent literature has recorded Fishfly Chauliodes and Alderfly Sialis larvae in wet tree holes and in pitcher plants (Fashing 1994, Hamilton et al. 1996, Pittman et al. 1996).

Comments: Alderflies have a high tolerance for polluted water.

Predators: A tiny 3 mm. Chalcid (KAL-sid) wasp called Trichogramma minutum parasitizes the eggs of Alderflies, Fishflies, the Viceroy butterfly and many moths. This wasp is native, but has been reared and released in peach orchards by Agriculture Canada since the 1930’s using stock obtained from Alderfly eggs. The wasp is now sold commercially.

Seven species of Sialis are recorded for Ontario:
S. concava: Head has some reddish smooth spots, area between eyes concave. Similar to S. infumata which has reddish spots much shorter and area between eyes convex. Banks, who described this species claims Van Duzee found one at Ridgeway, no date. Ross in 1937 noted that Walley found a male of this species in Power Glen (St. Catharines) in June, 1926 and the specimen is in the CNC (Canadian National Collection). Both locations are close to each other on the west side of the Niagara River. Also found in Guelph. 

S. infumata: Top of head has reddish, shiny flat streaks and spots extending to between antenna bases. Antenna slender. Cheeks yellowish or yellow infusion around eyes. Davis, 1903 maintains S. concava and S. infumata are the same, “S. concava Banks was said to differ in being always concave between the eyes. This, however, is not a constant character as shown by an examination of hundreds of specimens.” Reported from St. Martin’s Falls [Marten Falls] on Albany River (about middle northern Ontario). Also Ridgeway, Ottawa-Carleton, and Norman, Ontario.

S. itasca: Top of head has orange bars and spots. Narrow margin around eyes also orange. Wing base is dark brown, rest lighter to completely clear. Sister species to Sialis velata and females cannot be told apart from either S. velata or S. vagans. Found in Algonquin Park, June 18, 1922 by McDunnough and Ottawa-Carleton.

S. joppa: Top of head concave with raised lines and spots and a narrow ring around the eye, all yellowish. Lower legs lighter brown. Costal edge of wing has 18 to 12 cross-veins. Female has swollen cheeks, otherwise identical to male. Prefer streams. Larva and pre-pupa stages have been found inside pitcher plants. Found in Thunder Bay, Ontario.

S. mohri: Top of head concave, velvety. Costal edge of wing has 6 to 10 cross-veins, usually 7-8. Found in Ontario at Honey Harbor (Kenora), June 4 and 6, 1932; Ottawa West, June 21, 1920; Point Pelee, June 8, 1925; Rondeau Park, June 13, 1929.

S. vagans: Top of head concave with yellowish marks. Wings base half black, sometimes rest of the wings are much lighter to clear. Costal edge of wing has about 10 cross-veins. Sister species to S. itasca. Female cannot be told apart from either S. itasca or S. velata. Recorded from Algonquin Park, June 18, 1922. Lake of Bays (Huntsville), June 22, 1920. St. David’s (Niagara), June 11, 1926. Waubamik (North of Perry Sound) on July 10, 1915. 

S. velata: Male head entirely black; wings darker. Female is identical with S. itasca and S. vagans. Recorded from many locations in central and northern Ontario from Southampton to Ottawa. 

For information on synonyms, references and type specimens see next page