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Genus Overview
There are at least 7 species of this genus in North America, of which Hexagenia limbata is the most widespread and most famous among fly fishers, who eagerly anticipate a large "Hex hatch" of subimagoes ("duns") in lotic-depositional stretches of rivers and lakes with the appropriate marl substrate. The consistency of the sand-silt marl must be loose enough for larvae to burrow but dense enough for the walls of the burrow not to collapse. Undulation of a larva's body and the feathery gills on its back moves oxygenated water and fine particles of food through the U-shaped burrow. The food is gathered from the sides of the burrow or filtered from the water.
Characteristics
POLLUTION TOLERANCE
Southeast: 4.7 and higher
Upper Midwest: 6 and higher
Midwest: 3.1 and higher
Mid-Atlantic: 6 and higher
0 = least tolerant, 10 = most tolerant
FEEDING HABITS
Collector / Filterer
Collector / Gatherer
MOVEMENT
Burrower
DISTRIBUTION
Widespread (east of the Rocky Mtns.)
HABITAT
Lentic-littoral
Lotic-depositional
Diagnostic Characters
+ Expanded Character List
Order: Wings developing in wing pads. Mouthparts suitable for chewing. Gills present on tops and sides of abdomen. Segmented legs present. One tarsal claw per leg. Usually with 3 tails (sometimes 2).
Family: Large tusks project forward anteriorly from the face and are visible dorsally, when viewed laterally they curve upward. Foretibiae are fossorial (modified for burrowing: expanded or with tubercles). Ventral apex of each hind tibia acutely pointed. Abdominal gills on segments 2–7 are conspicuous dorsally, forked and elongate-lancolate, with fringed margins, giving the animal a fluffy appearance.
Genus: Frontal process of head rounded or truncate, never forked or pointed. Most antennal segments with whorls of setae, much longer than an antennal segment. Abdominal segment 1 with pair of small, forked, unfringed gills.