Dobsonflies are a subfamily of insects, Corydalinae, part of the Megalopteran family Corydalidae. The larvae (commonly called hellgrammites) are aquatic, living in streams, and the adults are often found along streams as well. The nine genera of dobsonflies are distributed in the Americas, Asia, and South Africa.
Etymology
The origin of the word "dobsonfly" is unclear. The term was in common use by at least 1878, as the records from the annual meeting of the Entomological Club of the American Association for the Advancement of Science that year contain:<blockquote>"In discussion it was stated that the somewhat peculiar name of the 'Hellgrammite Fly' for the Corydalis had been for many years in common use both on the Upper and Lower Mississippi and that the equally curious name of 'Dobson' was given to its larva, which was largely used for bait by the river fishermen."</blockquote>During this time there were also many more vernacular names for the larva. Below is a chart which shows some of the names in circulation and their locations in 1883, as heard from fishermen.
:::::{| class="wikitable"
|+
!Name
!Location Documented
|-
|Dobson
|Popular Use
|-
|Helgramite
|Popular Use
|-
|The Crawler
|Janesville, WI
|-
|Dam-worm
|Fox and Rock Rivers, WI
|-
|The Andy
|Fulton, NY
|-
|Black Crabs
|Fulton, NY
|-
|White Crabs
|Fulton, NY
|-
|Flying Crabs
|Fulton, NY
|-
|Scrabbles
|Broome County, NY
|-
|Molly-Grubs
|Broome County, NY
|-
|Black Worms
|Schenectady, NY
|-
|Flying Worms
|Schenectady, NY
|-
|Stone Crab
|Milford, NY
|-
|Sand Crab
|Milford, NY
|-
|Hell Devils
|Monroe, NY
|-
|The Dragon
|Schoharie, NY
|-
|Clipper
|Port Jervis, NY
Honesdale, PA
|-
|Conniption Bugs
|Towanda, PA
|-
|Bogart
|Portland, PA
|-
|Crawler
|Perkiomen, PA
|-
|Ho Jack
|Carlisle, PA
Pond Eddy, PA
|-
|Devil Catchers
|Wyalusing, PA
|-
|Snake Doctor
|Hanover, PA
|-
|Hiltamites
|Tulpehocken Dam, PA
|-
|Alugmites
|Tulpehocken Dam, PA
|-
|Stone Climber
|Schuylkill River, PA
|-
|Clipper Bug
|Schuylkill River, PA
|-
|The Devil
|Hazleton, PA
|-
|Water Grampus
|Lambertville, NJ
|-
|Goggle Goy
|Tumble, NJ
|-
|Black Crab
|Belvidere, NJ
|-
|Crock
|Interior of NJ
|-
|Red Crab
|Raleigh, NC
|-
|Yellow Crab
|Raleigh, NC
|-
|Hell Divers
|Raleigh, NC
|-
|Devil Catcher
|*location not given*
|-
|Dobsill
|*location not given*
|-
|Hell-Lion
|*location not given*
|-
|Kill-Devil
|*location not given*
|}
Description
Adult dobsonflies are some of the largest non-Lepidopteran insects of temperate zones such as the United States and Canada, with a wingspan of up to in some species of Corydalus. The Asian Acanthacorydalis fruhstorferi can have a wingspan of up to , making it the largest dobsonfly and the largest aquatic insect in the world by this measurement. The wings vary from a grayish to translucent shade, depending on the species, and the anal region of the hindwing is wide and folded at rest. Despite the large wings, adults are weak, fluttery fliers. The body is soft and coloration varies from yellow to dark shades of brown.
Adult males of many—but not all—species are easily recognized by their long, curving mandibles. Examples of species with large-mandibled males include the genera Acanthacorydalis, Corydalus and Platyneuromus, while in Neoneuromus, Nevromus, Neurhermes and Protohermes the sexes are similar. In Corydalus cornutus, a particularly long-mandibled species, these can reach up to in length and are used in competition for females. It is possible that the mandibles may have been selected as secondary sex characteristics used by females to evaluate males during courtship. Males cannot use these mandibles to bite because they are too long; on the other hand, females have short, heavily sclerotized mandibles which enable them to deliver powerful bites when threatened. "In spite of its disagreeable appearance it is in some respects very interesting to students of Nature study." The larvae, commonly called hellgrammites, are perhaps better known than the adults due to their more readily findable nature. They are unusual in that although they are generally aquatic, taking in dissolved oxygen through abdominal lateral filaments and tracheal gills, they also have spiracles that allow them to take in air directly when above water.
Larvae of dobsonflies differ from those of their sister clade, the alderflies, in that they bear eight pairs of lateral processes as well as anal prolegs with a pair of terminal hooks used to hold themselves to substrate, and also in that they lack a terminal filament. At the end of the abdomen is a pair of claw-like structures. Body color is black or dark brown.
Systematics
There are about sixty species of dobsonflies. suggests nine genera within Corydalinae, divided into four lineages. Working from "most basal" to "most derived" lineages, there are:
- The Protohermes lineage, containing the genera Neurhermes and Protohermes, distributed from Northwest India to Indonesia, China, and Japan.
- The Chloroniella lineage, containing the monotypic genus Chloroniella, found only in South Africa.
- The Nevromus lineage, containing the genera Acanthacorydalis, Nevromus, and Neoneuromus, distributed from Northwest India to Southeast Asia.
- The Corydalus lineage, containing the genera Platyneuromus, Chloronia, and Corydalus, distributed from southern Canada down to northern Argentina and south-east Brazil.
A 2025 study made the following phylogeny using molecular techniques:
Diet and behavior
The larvae of dobsonflies live along the rocky bottoms of streams. Chiefly active during the night, they ambush prey in the middle of riffles which supply plenty of oxygen and stir up prey. They are generalist predators; dissections have revealed that they primarily eat aquatic immatures of mayflies, caddisflies, stoneflies, and chironomid midges. Although the larvae spend most of their lives under rocks below water, locals along Virginia and Pennsylvania rivers have reported emergences, known as "hellgrammite crawlings," during thunderstorms.
The adults are also nocturnal, and are seldom seen as they hide under leaves in the canopy during the daytime. However, they do sometimes form aggregations under bridges or other structures along streams.
Oviposition occurs along rocky walls of streams at night, from May to September in Corydalus. The females deposit coin-size egg masses containing on average one thousand grey, cylindrical eggs, each egg about long and wide. This mass is covered by a layer of a chalky, white substance, which probably protects the eggs from desiccation and overheating. Females tend to deposit egg masses at relatively few sites, resulting in grouped egg masses. The pupae are yellow-orange with dark spots on the dorsum of the abdomen, covered in minute setae, and exarate (i.e. the developing appendages and mouthparts are attached only at their proximal ends). Finally, the pupae emerge from the chamber, leaving behind the larval and pupal skins. Smallmouth bass, in particular, are very attracted to hellgrammites as bait, due to the insects' active movement in the water. John Henry Comstock
Although not to the same extent as the larvae of mayflies and caddisflies, hellgrammites are intolerant of polluted waters and may have potential to be used as indicators of water quality.
As the adults are strongly attracted to lights, entomologists and collectors often use black light and mercury-vapor light traps to capture them.