Acentria ephemerella Olivier, 1791

Common Name: (European) aquatic/water moth

Synonyms and Other Names:

Acentria nivea, Acentropus niveus

Robert L. Johnson, Cornell University, Bugwood.orgCopyright Info

Robert L. Johnson, Cornell University, Bugwood.orgCopyright Info

Robert L. Johnson, Cornell University, Bugwood.orgCopyright Info

Identification: Early instar larvae of this aquatic moth species are stem boring or leaf mining caterpillars, while late instars live in shelters constructed of two or more pieces of host plant material. Larvae have no gills. The prothorax displays functional spiracles and the ventral surface exhibits biordinal crochets in horseshoe arrangements that are open mesally. Larval jaws are small and adapted for leaf-cutting (Johnson and Blossey 2002, Merritt and Cummins 1984, Peckarsky et al. 1993, Pennak 1978).           

Adult females are usually brachypterous, or with shortened, non-functional wings. They have hairy second and third legs for underwater swimming, and exhibit a plastron, or an incompressible gill full of hydrofuge hairs that traps gas on the ventral surface. Winged males, flightless females, and winged females (which are rare but occur occasionally) have a short, under-developed proboscis (Dierl and Reichholf 1977, Merritt and Cummins 1984, Munroe 1947, Pennak 1978).

Size: Adult moths are 5–9 mm long, early instar larvae are 0.25 mm long, and late instar case-building larvae are 10–12 mm long right before they pupate (Johnson and Blossey 2002).

Native Range: Acentria ephemerella is native to Europe, where it is very widespread (Johnson and Blossey 2002, Pennak 1978).

Map Key
This map only depicts Great Lakes introductions.

Great Lakes Nonindigenous Occurrences: Acentria ephemerella was recorded for the first time in the Great Lakes basin in 1938 at Minetto, New York on the Oswego River, which flows into Lake Ontario (Forbes 1938). It has also been collected from other parts of the Lake Ontario drainage, Lake Ontario proper, and Lake Erie and its drainage (Judd 1947, 1950; Munroe 1947).

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Acentria ephemerella are found here.

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
NY193819472Lake Ontario; Oswego

Table last updated 11/29/2022

† Populations may not be currently present.

* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: Acentria ephemerella is typically found in lentic macrophyte beds where filamentous algae are scarce and there is plenty of available oxygen. Adult females depend on diffusion across their plastron to respire and larvae living in attached cases at plant tips obtain oxygen from stems, trapping it in air bubbles in their shelters. Larvae are generalist herbivorous shredders and can feed on many plant taxa in Europe or North America, including: Lemna, Sparganium, Potamogeton, Myriophyllum, Hydrilla verticillata, Elodea canadensis, Ceratophyllum demersum, Anacharis canadensis, Trapa natans, and various reeds (Batra 1977, Brodersen 1995, Johnson and Blossey 2002, Judd 1953, Marlier 1978, Merritt and Cummins 1984, Mills et al. 1993, Peckarsky et al. 1993, Pennak 1978).

Egg laying often occurs twice a year, resulting in A. ephemerella emergence coinciding with two peaks in the biomass of milfoil (Myriophyllum spp.), one of its typical host plants. The latest generation of hatched larvae typically overwinters until spring of the following year. Not all North American populations produce two generations though, and when only one occurs, larvae usually overwinter in cocoons on macrophytes, then create new feeding shelters on plants the following year (Batra 1977, Johnson and Blossey 2002, Judd 1953, Painter and McCabe 1988).

The larval stage can last around 10.5 months and larval development generally requires temperatures below 22ºC, although higher water temperatures can be tolerated for short periods of time. Larvae that are ready to pupate cut the apical tip of their host plant and spin a cocoon between this piece of plant material and the main stem. Metamorphosis and adult reproduction both occur sometime in the summer. Adult males only live one or two days solely to breed and they copulate with females at the water surface. Wingless females are mostly nocturnally active and float on the water surface until they mate. Wingless females lay 100-300 eggs on host plants, while winged females usually lay fewer than 100 (Batra 1977, Buckingham and Ross 1981, Johnson and Blossey 2002, Judd 1953, Painter and McCabe 1988, Pennak 1978).

Means of Introduction: Acentria ephemerella was very likely accidentally released along with European plants brought to North America, such as Myriophyllum spicatum, Potamogeton crispus, and Trapa natans (Mills et al. 1993).

Status: Established where recorded.

Great Lakes Impacts:  

Current research on the environmental impact of Acentria ephemerella in the Great Lakes is inadequate to support proper assessment.

Acentria ephemerella is a generalist feeder, reportedly consuming a variety of macrophytes in North America and Europe, including Elodea canadensis, Ceratophyllum demersum, and Potamogeton spp., which are native to many of the Great Lakes states (Buckingham and Ross 1981, Gross et al. 2002, Johnson and Blossey 2002, Johnson et al. 1998). While feeding activity could suppress native macrophyte populations, A. ephemerella generally avoids feeding and building cocoons/retreats on the apical tip of these species, limiting damage to these plants (Johnson and Blossey 2002, Johnson et al. 1998). Furthermore, A. ephemerella appears to prefer the nonindigenous pest plant, Eurasian watermilfoil (Myriophyllum spicatum) over many native species (Gross et al. 2001, Johnson et al. 1998, Johnson and Blossey 2002). For instance, in Cayuga Lake, New York, the introduction of A. ephemerella resulted in significant declines in M. spicatum populations, while native macrophyte populations experienced recovery and growth.

However, native pondweeds (Potamogeton spp.) may also be a preferred resource of A. ephemerella (Johnson and Blossey 2002). In Europe, A. ephemerella heavily colonized both P. perfoliatus and M. spicatum, damaging, altering, and reducing P. perfoliatus populations (Gross et al. 2002, Miler and Straile 2010). A study at Lake Constance, Germany found A. ephemerella to be an ecosystem engineer through its control of the macrophyte communities (largely of P. perfoliatus) that many species, including young-of-the-year (YOY) and adult perch, stickleback, and pike, used as habitat (Miler 2008).

There is little or no evidence to support that Acentria ephemerella has significant socio-economic impacts in the Great Lakes.

Acentria ephemerella has a moderate beneficial effect in the Great Lakes.

Acentria ephemerella has had some success as a biological control agent of M. spicatum in the Great Lakes region. In Lakes Buckhorn and Scugog, part of the Trent Canal system flowing into Lake Ontario, populations of introduced Eurasian watermilfoil were decimated in the 1980s, likely due to grazing by A. ephemerella (Painter and McCabe 1988). In Cayuga Lake, the introduction of A. ephemerella was associated with a decline in M. spicatum populations and the recovery of native macrophytes (particularly Elodea canadensis) during the 1990s (Gross et al. 2001, Johnson et al. 1998, Johnson et al. 2000). The biocontrol ability of A. ephemerella is attributed to its feeding and building activities, which damage the apical meristems of M. spicatum and seriously hamper the plant’s growing ability. Milfoil can resist four A. ephemerella larvae per ten apical tips, but eight or more larvae or per ten tips causes very severe impacts (Johnson et al. 1998, Johnson et al. 2000, Painter and McCabe 1988).

Outside of the Great Lakes Basin in Brownington Pond, Vermont, herbivory by A. ephemerella and the weevil Euhrychiopsis lecontei was associated with declines in M. spicatum. Entire stands were pulled underwater as damaged plants with reduced buoyancy weighed down proximate healthy plants (Creed et al. 1992, Creed and Sheldon 1994). Experiments designed to test the ability of A. ephemerella as a biocontrol agent indicated that it can significantly reduce milfoil stem length and prefers to feed on M. spicatum over E. canadensis despite being a mainly generalist grazer (Creed and Sheldon 1994, Gross et al. 2001). A review on the biocontrol of Eurasian watermilfoil in North America agrees that A. ephemerella, along with E. lecontei and Cricotopus myriophylli, has the potential to be an effective control agent; however, populations in many study sites were lacking the densities of A. ephemerella needed to be fully effective (Newman 2004).


Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Acentria ephemerella is used for biological control of Eurasian watermilfoil (Myriophyllum spicatum).  Its population is best controlled by elimination of its host plants – which are predominantly Eurasian watermilfoil but also may, to a lesser extent, include a variety of other native and nonindigenous plants (Cornell 2004).

Mechanical harvesting, herbicide applications, benthic barriers, and water drawdowns all remove either A. ephemerella individuals or their habitat (aquatic plants) from waterways (Cornell 2004).

This species is susceptible to herbicide control of its host plants (Cornell 2004).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: Some earlier authors believe that A. ephemerella is native to North America, given its wide distribution and inconspicuous appearance, which may have made it hard to identify in the past (Munroe 1947). However, most recent literature indicates that it was introduced with European plants. In North America, A. ephemerella was first recorded in 1927 from Montreal, Quebec, Canada on the St. Lawrence River (Buckingham and Ross 1981, Mills et al. 1993).

In spite of the documented strong negative effects of high densities of A. ephemerella on M. spicatum, this aquatic moth probably only has a weak negative effect on many host plants in general. Such macrophytes as M. spicatum, T. natans, and P. crispus generally experience such low costs in acting as hosts to A. ephemerella that the relationship can even be classified as commensal (Ricciardi 2001). Moreover, it is possible that herbivore damage to milfoil stems causes fragmentation and aids dispersal of some fragments that are still viable (Creed and Sheldon 1994).

In ITIS, Acentropus niveus and Acentria niveus are both listed as valid but unverified species names (citing 1996 Code). Bernd Blossey (Cornell U., pers. comm.) advised that Acentria ephemerella is the correct, valid name per:  Passoa, S. 1988. Systematic positions of Acentria ephemerella (Denis & Schiffermiiller), Nymphulinae, and Schoenobiinae based on morphology of immature stages (Pyralidae). J. Lepidopt. Soc. 42: 247-262.

References: (click for full references)

Batra, S.W.T. 1977. Bionomics of the aquatic moth Acentropus niveus, a potential biological control agent for Eurasian water milfoil and Hydrilla. Journal of the New York Entomological Society 85(3):143-152.

Brodersen, K.P. 1995. The effect of wind exposure and filamentous algae on the distribution of surf zone macroinvertebrates in Lake Esrom, Denmark. Hydrobiologia 297:131-148.

Buckingham, G.R., and B.M. Ross. 1981. Notes on the biology and host specificity of Acentria nivea (=Acentropus niveus). Journal of Aquatic Plant Management 19:32-36.

Cornell University Experimental Ponds.  2004.  Acentria ephemerella.  Downloaded 10/23/13.

Creed, R.P., Jr., and S.P. Sheldon. 1994. The effect of two herbivorous insect larvae on Eurasian watermilfoil. Journal of Aquatic Plant Management 32(Jan.):21-26.

Creed, R.P., Jr., S.P. Sheldon, and D.M. Cheek. 1992. The effect of herbivore feeding on the buoyancy of Eurasian watermilfoil. Journal of Aquatic Plant Management 30:75-76.

Dierl, W., and J. Reichholf. 1977. Wing reduction in Lepidoptera as an adaptive strategy. Spixiana 1(1):27-40.

Forbes, W.T.M. 1938. Acentropus in America (Lepidoptera, Pyralidae). Journal of New York Entomological Science 46:338.

Gross, E.M., R.L. Johnson, and N.G. Hairston, Jr. 2001. Experimental evidence for changes in submersed macrophyte species composition caused by the herbivore Acentria ephemerella (Lepidoptera). Oecologia 127:105-114.

Johnson, R.L., and B. Blossey. 2002. Eurasian Watermilfoil. Pp. 79-90 in R. Van Driesche et al., eds. Biological Control of Invasive Plants in the Eastern United States, USDA Forest Service Publication FHTET-2002-04. 413 pp.

Johnson, R.L., E.M. Gross, and N.G. Hairston, Jr. 1998. Decline of the invasive submersed macrophyte Myriophyllum spicatum (Halorgaceae) associated with herbivory by larvae of Acentria ephemerella (Lepidoptera). Aquatic Ecology 31:273-282.

Johnson, R.L., P.J. Van Dusen, J.A. Toner, and N.G. Hairston, Jr. 2000. Eurasian watermilfoil biomass associated with insect herbivores in New York. Journal of Aquatic Plant Management 38:82-88.

Judd, W.W. 1947. Acentropus niveus Olivier (Lepidoptera, Pyralidae) at Hamilton, Ontario. The Canadian Entomologist 79:119.

Judd, W.W. 1950. Acentropus niveus (Oliv.) (Lepidoptera: Pyralidae) on the north shore of Lake Erie with a consideration of its distribution in North America. The Canadian Entomologist 82:250–253.

Judd, W.W. 1953. A study of the population of insects emerging as adults from the Dundas Marsh, Hamilton, Ontario, during 1948. American Midland Naturalist 49(3):801-824.

Marlier, G. 1978. Aquatic insects. Naturalistes Belges 59(1-2):37-44.

Merritt, R.W., and K.W. Cummins, eds. 1984. An Introduction to the Aquatic Insects of North America 2nd ed. Kendall/Hunt Publishing Company, Dubuque, Idaho. 722 pp.

Miler, O. 2008. The aquatic moth Acentria ephemerella as a key species in submerged aquatic vegetation – direct and trait-mediated interactions with predators and food plants. Dissertation, University of Konstanz, Limnological Institute, 121 pp.

Miler, O., and D. Straile. 2010. How to cope with a superior enemy? Plant defence strategies in response to annual herbivore outbreaks. Journal of Ecology 98:900-907.

Mills, E.L., J.H. Leach, J.T. Carlton, and C.L. Secor. 1993. Exotic species in the Great Lakes: a history of biotic crises and anthropogenic introductions. Journal of Great Lakes Research 19(1):1-54.

Munroe, E.G. 1947. Further North American records of Acentropus niveus (Lepidoptera, Pyralidae). The Canadian Entomologist 79:120.

Newman, R.M. 2004. Invited review: Biological control of Eurasian watermilfoil by aquatic insects: basic insights from an applied problem. Archiv für Hydrobiologie 159(2):145-184.

Painter, D.S., and K.J. McCabe. 1988. Investigation into the disappearance of Eurasian water milfoil from the Kawartha Lakes, Canada. Journal of Aquatic Plant Management 26:3-12.

Peckarsky, B.L., P.R. Fraissinet, M.A. Penton, and D.J. Conklin, Jr. 1993. Freshwater Macroinvertebrates of Northeastern North America. Cornell University Press, Ithaca, New York State. 442 pp.

Pennak, R.W. 1978. Fresh-water Invertebrates of the Unites States. 2nd edition. John Wiley and Sons, Inc., New York, New York State. 803 pp.

Ricciardi, A. 2001. Facilitative interactions among aquatic invaders: is an “invasional meltdown” occurring in the Great Lakes? Canadian Journal of Fisheries and Aquatic Sciences 58:2513-2525.

Other Resources:
Author: Kipp, R.M, J. Larson, and A. Fusaro

Contributing Agencies:

Revision Date: 9/13/2019

Citation for this information:
Kipp, R.M, J. Larson, and A. Fusaro, 2022, Acentria ephemerella Olivier, 1791: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 9/13/2019, Access Date: 11/29/2022

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.