Hexagenia atrocaudata
McDunnough, 1924
Lake Hex
Hexagenia atrocaudata is a burrowing in the Ephemeridae, known from North American lakes and rivers. As a member of the common burrower mayflies, it spends the vast majority of its life as an aquatic nymph in bottom sediments, emerging as a short-lived winged for . Adults lack functional mouthparts and do not feed. Mass synchronous emergences can occur, producing swarms that attract fish and anglers alike. The species serves as an important indicator of clean freshwater and provides substantial food resources for aquatic and terrestrial .
Pronunciation
How to pronounce Hexagenia atrocaudata: /ˌhɛksəˈdʒiːniə ˌætroʊkɔˈdeɪtə/
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Habitat
Lakes and rivers with clean, well-oxygenated water and suitable bottom substrates of silt or sand for burrowing. Nymphs construct U-shaped burrows in lake and stream bottoms. are aerial but remain near water bodies during their brief adult stage.
Distribution
North America; specifically recorded from the Nearctic region including the Great Lakes area and associated river systems.
Seasonality
typically occurs in summer months; exact timing varies with latitude and local water temperature conditions. Mass emergences have been documented in June and July in the Great Lakes region.
Diet
Nymphs feed on and decomposing organic matter filtered from the water column or gathered from sediment surfaces. possess non-functional mouthparts and do not feed.
Life Cycle
with distinct aquatic nymph and winged stages. Nymphal development lasts approximately one to three years depending on conditions. Adults emerge synchronously in large numbers, once after (subimago to ), mate, and die within days. Females deposit on water surfaces.
Behavior
Nymphs are burrowers, constructing and inhabiting U-shaped tunnels in bottom sediments. exhibit synchronized mass , forming dense mating swarms near water bodies. Adults are attracted to light.
Ecological Role
Nymphs serve as bioturbators, mixing sediments and contributing to nutrient cycling in aquatic . Both nymphs and are critical food sources for fish, birds, amphibians, and other . The is a key component of the EPT (Ephemeroptera-Plecoptera-Trichoptera) index used to assess water quality.
Human Relevance
Important for sport fishing as a primary food source for trout and other game fish; emergences trigger feeding frenzies. Fly fishermen imitate both nymphal and adult stages with artificial flies. Mass emergences can create nuisance conditions requiring cleanup of dead insects from roads and structures. The is celebrated at regional festivals such as the Bay-Rama Festival in Michigan.
Similar Taxa
- Hexagenia limbataAlso a common burrower mayfly in the same with similar and appearance; distinguished by subtle morphological differences in genitalia and caudal filaments requiring expert examination.
- Hexagenia bilineataAnother congeneric burrower with overlapping range and preferences; identification relies on detailed examination of abdominal coloration and tail markings.