Hydropsyche alternans

Larvae construct silken mesh nets attached to retreats in rock crevices, distinguishing them from other caddisfly families. Final instar larvae reach approximately 20 mm. Adults emerge synchronously from summer solstice through mid-July. Distinguished from other Hydropsyche species by habitat specificity for wave-swept lacustrine surf zones combined with Great Lakes distribution.

Rocky, wave-swept surf zones of large lakes, particularly sandstone pavement and boulder substrates in 1-2 m depth. Requires solid substrates with cracks and crevices for net and retreat construction, and moving water to deliver food. Also occurs in cold, swift rivers and shallow lake margins with fluctuating water quality.

Currently abundant only in Lake Superior. Extirpated from Lakes Michigan, Huron, Erie, and Ontario. Broader modern range extends northwest to Gulf of Alaska drainage and east through former Glacial Lake Chippewa basin to Lake Champlain. Historical distribution includes Lake Winnipeg. Fossil records from 80,000-year-old deposits north of modern Lake Ontario.

Adult emergence broadly synchronous from summer solstice through mid-July. Mating and oviposition occur early to mid-summer. Larval development spans approximately 10 months with most growth in first 100 days. Overwintering as ultimate or penultimate instars. Pupation follows spring ice-out.

Omnivorous mix of benthic, pelagic, and terrestrial resources: diatoms (epilithic and planktonic), small arthropods, sloughed periphyton, fungal hyphae, and detrital material. Food captured in nets from wave-driven currents, gleaned with labral bristles, or grazed directly from substrates.

Univoltine. Five larval instars with head capsule width increasing by factor of ~1.5 between instars. Rapid growth through summer into fall, overwintering as 4th or 5th instars. Pupation in spring following ice-out. Adults emerge mid-summer.

Constructs silken mesh nets rigged to retreats in rock crevices to filter food from wave-driven currents. Females swim to surf-exposed substrates to oviposit. Tolerant of fluctuating water quality including cyanobacterial blooms.

Suspension-feeding omnivore forming energetic links between coastal, nearshore, and offshore food webs. Trophic position ranges from primary consumer to invertebrate predator. Wave action limits sediment accumulation, promoting benthic diatom establishment. These ecosystem connections have been lost in lower Great Lakes due to Dreissena mussel dominance.

Serves as indicator species for pre-invasion ecological conditions in Great Lakes. Population collapse following Dreissena mussel invasion demonstrates profound ecosystem reorganization in North American large lakes.

• Other HydropsychidaeRiverine relatives share similar life history and trophic niche, but H. alternans is distinguished by lacustrine surf-zone habitat specialization and Great Lakes distribution.
• Dreissena musselsNot a taxonomic relative, but the invasive mussels that displaced H. alternans throughout four of five Great Lakes through ecosystem reorganization, not direct competition.

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• An Ecological Profile of Hydropsyche alternans (Trichoptera: Hydropsychidae) in Lake Superior, the Last Stronghold of a Once-Dominant Great Lakes Surf Zone Caddisfly