Acentria ephemerella

Distinguished from other aquatic moths by the unique combination of permanently aquatic adult females with brachyptery and leg swimming hairs. Males can be identified by their attraction to light in large swarms on warm humid nights. Larvae are cryptic and difficult to detect; case-building behavior in late instars helps distinguish from some other aquatic caterpillars.

Adult females typically have underdeveloped, non-functional wings and spend their entire lives underwater with additional swimming hairs on the second and third legs. A rare winged terrestrial female morph exists with fully developed wings. Males have normal wings and are fully terrestrial. All adults possess an under-developed proboscis. Larvae are aquatic and case-building in late instars.

Lentic freshwater habitats including ponds, lakes, and marshes. Closely associated with submersed macrophytes, particularly Myriophyllum spicatum. Larvae use apical tips of macrophytes as summer refuges and stems as winter refuges for hibernation.

Native to Europe where widespread; established in North America with confirmed populations in New York State lakes including Cayuga Lake (first observed 1991) and Seneca Lake. Present in 25 of 26 surveyed lakes in New York State.

Adult males active on warm humid nights, attracted to light and capable of swarming in thousands. Larvae reach high densities (27-100 m⁻²) in summer; hibernate in stems at densities up to 500 m⁻² in late fall.

Larvae are herbivorous, feeding on aquatic plants including pondweeds (Potamogeton spp.), Canadian waterweed (Elodea canadensis), and Eurasian watermilfoil (Myriophyllum spicatum). Laboratory studies indicate ability to consume various macrophytes, though field populations show strong association with M. spicatum.

• Myriophyllum spicatum - primary host plantEurasian watermilfoil; larvae use apical tips for summer refuges and stems for winter hibernation. Preferred over native species in field settings.
• Potamogeton spp. - food plantpondweeds
• Elodea canadensis - food plantCanadian waterweed

Aquatic larvae with terrestrial adults. Larvae are case-building in late instars and generally overwinter in cocoons on macrophytes. Hibernation occurs in milfoil stems during late fall and winter. Pupation and adult emergence timing not explicitly documented in sources.

Adult males live 1-2 days solely to breed, mating with aquatic females at the water's surface. Females remain underwater throughout their entire adult lives—a unique behavior among moths. Larvae exhibit cryptic habits making them difficult to detect. High-density grazing causes severe damage to apical meristems of host plants.

Significant herbivore of submersed macrophytes. Acts as a biocontrol agent contributing to decline of invasive Eurasian watermilfoil; larval herbivory associated with marked decrease in M. spicatum biomass and concurrent increase in native macrophyte abundance. At high densities, can substantially alter aquatic plant community composition.

Used as an agent of biological pest control against Eurasian watermilfoil (Myriophyllum spicatum), a noxious invasive aquatic plant. Valued by some anglers as trout prey, though many anglers remain unaware of its significance. Males attracted to light in large numbers can be a nuisance near water bodies.

• Nymphula nitidulataBoth are aquatic crambid moths with aquatic larvae, but N. nitidulata has fully winged adults of both sexes that are terrestrial, and larvae are semi-aquatic living on wetland plants above the water line rather than fully submerged.
• Bellura melanopygaBoth have aquatic larvae feeding on water lilies, but B. melanopyga larvae breathe by periodic surfacing through specialized spiracles and adults are fully winged and terrestrial.
• Hyposmocoma spp.Some Hawaiian species have aquatic or amphibious larvae, but adults are fully winged and terrestrial; no brachypterous aquatic female morph exists.

• aquatic moth
• biocontrol
• sexual dimorphism
• brachyptery
• invasive species management
• freshwater ecology

• BugGuide
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• The Lepidopteran Life Aquatic
• Comparative Cytogenetics | Blog - Part 2
• Decline of the invasive submersed macrophyte Myriophyllum spicatum (Haloragaceae) associated with herbivory by larvae of Acentria ephemerella (Lepidoptera)
• The genome sequence of the Water Veneer, Acentria ephemerella (Denis & Schiffermüller, 1775).