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Species Corydalus cornutus - Eastern Dobsonfly

Eastern Dobsonfly - Corydalus cornutus - female Is it some form of nasty looking dragonfly? - Corydalus cornutus - female cross breed? - Corydalus cornutus ID request - Corydalus cornutus birthday dobsonfly - Corydalus cornutus - female Unknown bug - Corydalus cornutus - male Eastern Dobsonfly - Corydalus cornutus - female big bug - Corydalus cornutus
Classification
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Megaloptera (Alderflies, Dobsonflies, and Fishflies)
Family Corydalidae (Dobsonflies and Fishflies)
Subfamily Corydalinae
Genus Corydalus (Dobsonflies)
Species cornutus (Eastern Dobsonfly)
Other Common Names
Hellgrammite (larva), Dobson (larva, see below), Hellgrammite Fly, Horned Corydalus, man-eater (larva (1)), Grampus (from Krampus, a European mythological monster), go-devil, Le Corydale cornu (French)
Synonyms and other taxonomic changes
Corydalus cornutus (Linnaeus, 1758). Synonyms:
Corydalus crassicornis
Corydalus inamabilis
Explanation of Names
Species name cornutus from Latin cornut horned (2). See Remarks for discussion of English common names.
Size
Up to 50 mm body length, 100-140 mm to tip of wings. Wingspan to 125 mm.
Identification
Typical Dobsonfly, most widespread species in Eastern North America. Males have spectacular mandibles. Compare Chauliodes, which has a different shape to thorax and head, lacks enlarged mandibles.
Arnett (3) mentions the white spots in many of the wing cells and the large mandibles as identifying characteristics for this genus.

Range
Eastern North America (only species in east)
Habitat
Near fast-flowing streams. Attracted to lights.
Season
Late spring-early fall (adults). June-September (North Carolina)
Food
Adults likely do not feed.
Life Cycle
Eggs laid in masses of 100-1,000 on rocks (or vegetation) above the waterline of streams. Larvae drop, or crawl into water. Larvae aquatic predators, live in streams. Two-three years are spent in larval stage, at end of this time larvae crawl out of stream and form pupal cell under log, rock, etc. and overwinter. Adults emerge spring to summer. Illustration:
  
The huge mandibles of the males are used to grasp the females during mating. The females, with much smaller jaws, can apparently bite more effectively. Although neither male nor female feed in the adult stage, they may use their mandibles for self-defense.
Remarks
The etymology of hellgrammite is said to be "obscure" (4) as is the origin of dobsonfly, though the latter would appear to be related (by folk etymology?) to the surname Dobson (Internet searches). The Century Dictionary (1) and other sources note that both terms were bestowed by fisherman, as the larvae are used as bait. The terms seem to date to at least the late 19th century--The Century Dictionary quotes usage of both terms by The Standard Natural History (1884-1885), volume II, p. 156 (link):
At this period (larval stage) of their existence they are much sought after as fish-bait, having a very tough integument, so that one larva suffices to catch several fish; and they are called by fishermen "crawlers," "dobsons," and sometimes, we hope rarely, "hellgrammites."
Note that the name "dobson" was used for the larva, and that dobsonfly (for the adult) is derived from that. The quotation above, in turn, was from Walsh and Riley, The American Entomologist, apparently vol. 1 #4 (1861), p. 62 (Biodiversity Heritage Library link). The original reference mentions the term "hellgrammite", but does not use "dobson".
Speculation. Hellgrammite might be a compound of hell plus grim (fierce, cruel) plus suffix ite (creature, being, or mite small being). The Online Etymology Dictionary notes:
...It (grim, Old English grimma) also had a verb form in O.E. (Old English), grimman (class III strong verb; past tense gramm, p.p. grummen). O.E. also had a noun, grima "goblin, specter," perhaps also a proper name or attribute-name of a god, hence its appearance as an element in place names. As a noun meaning "a form of bogey or haunting spirit," first recorded 1628.
Again, this is speculation, but the Old English forms grimm, gramm are certainly suggestive. A folk etymology origin (from a Native American word?) certainly seems possible as well, and would not be mutually exclusive with the speculation above.
Speculation(2). The word "dobson" sounds like a folk etymology for another word foreign to English speakers. Possibly the origin is a Native American word for the larva. Another possibility is that it is a reference to another aquatic creature, the dolphin (from French daulphin, see Wikipedia--Dolphin, Online Etymology Dictionary--dolphin). Note that originally "dobson" was a term for the larva.
See Also
Dark Fishflies, Nigronia
Gray Fishflies, Neohermes
Fishflies, Chauliodes
Three other species in this genus apparently have very limited distribution in North America:
Corydalus luteus - South Texas
Corydalus texana - SW US west of the Rocky Mountains
Corydalus bidenticulatus - Arizona
Print References
Arnett, p. 345, fig 23.6 (3)
Borror, entry for cornut (2)
Borror and White, pp. 140-141 (5)
Bowles, D.E. 1990. Life history and variability of secondary production estimates for Corydalus cornutus (Megaloptera: Corydalidae) in an Ozark stream. J. Agric. Entomol. 7: 61-70.
Brimley, p. 29 (6)
Gordh, entry for hellgrammite (4)
Milne, p. 522, figs. 332, 333 (7)
Swan and Papp, p. 182, fig. 189 (8)
The Century Dictionary--entries for hellgrammite, man-eater (defn. #4) (1)
Internet References
Clemson University--Corydalus - Dobsonfly
Insects of Quebec--Corydale cornu--excellent photos, shows male, female, larva
Megaloptera of Florida--Dobsonflies
TAMU--Dobsonfly
Beetles in the Bush (20 February 2012)--Grampus and go-devil
Works Cited
1.The Century Dictionary: an encyclopedic lexicon of the English language
2.Dictionary of Word Roots and Combining Forms
Donald J. Borror. 1960. Mayfield Publishing Company.
3.American Insects: A Handbook of the Insects of America North of Mexico
Ross H. Arnett. 2000. CRC Press.
4.A Dictionary of Entomology
George Gordh, David H. Headrick. 2003. CABI Publishing.
5.A Field Guide to Insects
Richard E. White, Donald J. Borror, Roger Tory Peterson. 1998. Houghton Mifflin Co.
6.Insects of North Carolina
C.S. Brimley. 1938. North Carolina Department of Agriculture.
7.National Audubon Society Field Guide to Insects and Spiders
Lorus and Margery Milne. 1980. Knopf.
8.The Common Insects of North America
Lester A. Swan, Charles S. Papp. 1972. Harper & Row.