[2] 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 18 cm (7.1 in) in some species of Corydalus.

[4][5] 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.

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.

[3] Males of many species will also produce nuptial gifts in the form of packages of nutrient-rich spermatophores that are eaten by the female partner after mating.

Corydalinae is distinguished from closely related clades by the following synapomorphies (with exceptions in a few species): quadrate head with a postocular spine, ridge, and plane, non-pectinate antennae, four crossveins between the radius and the radial sector, and distinctive male terminalia with a well developed ninth gonostylus.

[3] In regards to the larvae, entomologist John Henry Comstock wrote in his 1897 book Insect Life,[1] "In spite of its disagreeable appearance it is in some respects very interesting to students of Nature study."

[12] They are generalist predators; dissections have revealed that they primarily eat aquatic immatures of mayflies, caddisflies, stoneflies, and chironomid midges.

[13] 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.

[9] The dobsonfly may be attracted by mercaptan, an indicator additive in natural gas and propane, and may behave as an animal sentinel in the presence of these gases.

Males compete with each other for females, aggressively fluttering the wings and trying to place their long mandibles underneath the body of the opponent in order to flip him into the air.

After copulation, the female proceeds to spread her legs wide apart, curl the abdomen under the chest, and eat the gelatinous part of the spermatophore.

[9] When they have finally reached maturity, the larvae leave the water and find a rock, log, or anthropogenic debris, typically close to the stream but sometimes up to 40 m away.

[9][17] 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).