Description

Taxonomy

Kingdom	Phylum	Class	Order	Family	Genus
Animalia	Hexapoda	Insecta	Diptera	Syrphidae	Eristalis

Synonyms

Musca tenax; Musca porcina; Conops vulgaris; Conops fuscus; Elophilus tenax; Syrphus tenax; Tubifera tenax

Invasion History

Chesapeake Bay Status

First Record	Population	Range	Introduction	Residency	Source Region	Native Region	Vectors
1916	Established	Stable	Introduced	Unconfirmed	Europe	Eurasia	Agriculture(Agricultural Weed),Natural Dispersal(Natural Dispersal)

History of Spread

Eristalis tenax (Hoverfly, Rat-Tailed Maggot) is now cosmopolitan, but probably orginated in Europe or the Middle East (Stone et al. 1965). Williston (1886) describes its early history in North America: 'Prior to 1874 or 1875, the species had never been recognized by dipterologists, although such an able collector as Baron Osten Sacken had spent many years in the study of our dipterous fauna. At present it is very abundant in New England, and I have seen specimens from the Central and Pacific states. In Professor Riley's collection, however, there is a specimen bearing the date of 1870, and presumably captured in the Western States somewhere. Upon calling this gentleman's attention to the specimen, he assured me that the species had long been familiar to him about privies and out-houses, where they are known to breed. It seems probable to me that the species had been present in North America for many years, but had never been recognized.' Eristalis tenax is now known from AK - Labrador and south to CA and FL (Stone et al. 1965).

In the Chesapeake Bay region, Eristalis tenax was probably present by the late 1800's, but the first published record is Banks et al. (1916), who reported it as 'very common; taken everywhere' in the vicinity of Washington DC. Based on its wide North American distribution, and its general habitat preference, it is probably found throughout the Chesapeake region wherever water is contact with large quantities of animal manure or sewage. The one specific record we have from tidal waters is that by Lubin (1972) for the Bush River subestuary (near Edgewood MD, Harford County) of the upper Bay. Eristalis tenax larvae were reported from several Bush River tributaries: Winters Run, Cranberry Run, and from the upper main stem of the estuary. 'Eristalis' sp. larvae were reported from the Potomac by Lippson et al. (1979).

History References - Banks et al. 1916; Lippson et al. 1979; Lubin 1972; Stone et al. 1965; Williston 1886

Invasion Comments

Residency - Eristalis spp. adults are abundant pollinators of terrestrial plants, but they have distinctive aquatic larvae (Stubbs 1993), 'Rat-Tailed Maggots', which are found in habitats rich in organic material. Eristalis tenax larvae are normally found in 'organically rich and polluted ditches and drains' (Stubbs 1993), or 'liquid manure' (Heal 1990). This species is included here because larvae were reported from the Bush River, a moderately polluted tributary of the upper Bay (Lubin 1972). Based on this fly's preference for very enriched habitats for egg-laying (Heal 1990), it is unlikely to be a regular resident.

Vector(s) of Introduction - Eristalis tenax probably transported as adults with ornamental plants, or as larvae with animal manure. Natural dispersal from elsewhere in North America is also possible.

History of Spread- No details were given on how Lubin (1972) identified E. tenax larvae. Since other Eristalis spp. are common in the Chesapeake region (Banks et al. 1916), we are unsure of the certainty of the identification. However, based on the species' habitat preference (Heal 1990; Stubbs 1993) and abundance in the region (Banks et al. 1916), its occurrence as an 'boundary resident' is plausible, especially near farms and sewage outfalls.

Ecology

Environmental Tolerances

	For Survival		For Reproduction
	Minimum	Maximum	Minimum	Maximum
Temperature (ºC)
Salinity (‰)	0.0		0.0
Oxygen
pH
	Salinity Range	fresh-oligo

Age and Growth

	Male	Female
Minimum Adult Size (mm)
Typical Adult Size (mm)
Maximum Adult Size (mm)
Maximum Longevity (yrs)
Typical Longevity (yrs

Reproduction

	Start	Peak	End
Reproductive Season
Typical Number of Young Per Reproductive Event
Sexuality Mode(s)
Mode(s) of Asexual Reproduction
Fertilization Type(s)
More than One Reproduction Event per Year
Reproductive Startegy
Egg/Seed Form

Impacts

Economic Impacts in Chesapeake Bay

The hoverfly Eristalis tenax has no signicant economic impacts in Chesapeake Bay proper. In terrestrial environments, it may be beneficial to agriculture and horticulture as a pollinator (Stubbs 1993).

References- Stubbs 1993

Economic Impacts Outside of Chesapeake Bay

The hoverfly Eristalis tenax is cosmopolitan, and has probably been introduced in many of the places where Western agriculture is practiced (Stone et al. 1965; Stubbs 1993; Williston 1886). In terrestrial environments, it may be beneficial to agriculture and horticulture as a pollinator (Stubbs 1993).

References - Stone et al. 1965; Stubbs 1993; Williston 1886

Ecological Impacts on Chesapeake Native Species

Impacts of the hoverfly, Eristalis tenax, on native Chesapeake biota are not known. The larvae probably occur only occasionally in tidal waters. Adult Eristalis sp. are important pollinators in terrestrial environments. Based on its abundance in the Washington DC region and elsewhere (Banks et al. 1916; Stone et al. 1965), E. tenax probably is an important pollinator, but larval habitat preferences may concentrate it near human dwellings, farms, and sewage outfalls (Heal 1990; Stubbs 1993).

References - Banks et al. 1916; Heal 1990; Stone et al. 1965; Stubbs 1993

Ecological Impacts on Other Chesapeake Non-Native Species

Impacts of the hoverfly, Eristalis tenax, on introduced Chesapeake biota are not known. The larvae probably occur only occasionally in tidal waters. Adult Eristalis sp. are important pollinators in terrestrial environments. Based on its abundance in the Washington DC region and elsewhere (Banks et al. 1916; Stone et al. 1965), E. tenax probably is an important pollinator of garden plants (Heal 1990; Stubbs 1993).

References- Banks et al. 1916; Heal 1990; Stone et al. 1965; Stubbs 1993

References

Banks, Nathan; Greene, C. T.; McAtee, W. L.; Shannon, R. C. (1916) District of Columbia Diptera: Syrphidae, Proceedings of the Biological Society of Washington 29: 173

Heal, Jon (1990) Eggs and egg-laying: Some details about hoverflies, Dipterists Digest 6: 27-29

Lippson, Alice J.; Haire, Michael S.; Holland, A. Frederick; Jacobs, Fred; Jensen, Jorgen; Moran-Johnson, R. Lynn; Polgar, Tibor T.; Richkus, William (1979) Environmental Atlas of the Potomac Estuary, , Baltimore, MD. Pp.

Lubin, Jane (1972) Benthic analysis and shoreline vegetation., In: (Eds.) Evaluation and Predictions of the Eutrophication Potential of the Bush River Sub-Estuary.. , Towson, MD. Pp. 88-103

Stone, Alan; Sabrosky, Curtis; Wirth, Willis W.; Foote, Richard; Coulson, Jack H. (1965) A catalog of the Diptera of North America north of Mexico, , Washington, D.C.. Pp.

Stubbs, Alan E. (1993) British Hoverflies: An Illustrated Identification Guide, , . Pp.

Williston, Samuel W. (1886) Synopsis of the North American Syrphidae, United States National Museum Bulletin 31: 1-335

Eristalis tenax

Invertebrates