Species Corydalus cornutus - Eastern Dobsonfly

Hellgrammite (larva), Dobson (larva, see below), Hellgrammite Fly, Horned Corydalus, man-eater (larva (1)) Le Corydale cornu (French)

Corydalus cornutus (Linnaeus, 1758). Synonyms:

Species name cornutus from Latin cornut horned (2). See Remarks for discussion of English common names.

Up to 50 mm body length, 100-140 mm to tip of wings. Wingspan to 125 mm.

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.

Eastern North America (only species in east)

Near fast-flowing streams. Attracted to lights.

Late spring-early fall (adults). June-September (North Carolina)

Adults likely do not feed.

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.

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):

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:

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.

Three other species in this genus apparently have very limited distribution in North America: