Distribution of Sialis velata in North America.

The genus Sialis is globally distributed with about 23 species living in North America (Locklin et al. 2006). Fossils of Sialis have yet to be found in North America, but have been discovered in other parts of the world such as the Tertiary of Europe, Asia Minor, and Australia (Engel 2004). Sialis velata is the most widespread species within the genus Sialis inhabiting the eastern U.S. and Canada (Anderson et al. 2003).

Geography plays a role in the life history of these insects providing variation in how long their life cycle lasts. The temperature of the environments in which Sialis velata lives in causes the variation. The warmer the environment, the larger numbers of this species are produced. Fewer numbers are produced at northern latitudes than southern latitudes because summers and warm weather are short (Locklin et al. 2006).

The habitats of the alderfly differ between the larvae phase and adult phase. Larvae are aquatic and can be found in slow moving water that has soft sediment at the bottom needed for burrowing. When larvae hatch, they drop into the water and live aquatically until they reach the pupal phase. To enter the pupal phase, the larvae crawl onto the banks of a stream or lake and burrow in the sand until metamorphosis is complete. When the adults hatch, they are now terrestrial insects that live on land close to the waters edge (Anderson et al. 2003)

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Alderfly Larvae. Photo by Neil Phillips