Scientific name: Corydalus cornutus
Common name: Hellgramite (larvae), Dobson Fly (adult)
As you might have guessed by looking at it, hellgramite is a predator--and it's a big one! Hellgramites are usually three-inches long.
This creature is in the insect order Megaloptera. Adult Megalopterans include insects commonly known as fishflies, alderflies and dobsonflies. Larval Megalopterans, specifically those in the family Corydalidae, are known as hellgramites. The species in the genus Corydalus are among our largest North American insects.
Hellgramites are not very common. They are generally found under big rocks in larger, well-aerated streams and rivers. Being large and "showy" insects they tend to be secretive, hiding tightly wedged under large rocks to avoid predation (being eaten by something else).
As they lie under rocks, they feed on pretty much any insect or invertebrate that crawls by. They don't chase creatures that swim by, because they lack the ability to swim strongly in the fast-flowing water environment that they live in. Actually, they don't swim very well in any water.
As you might be able to tell, they have very large pincers. They use these powerful pincers to catch and tear up their prey. When handling these creatures you have to be very careful because they move very fast (it was hard to take their picture!), and can inflict a painful bite (ouch!). They're not poisonous, but they are powerful enough to draw blood. So if you catch one in a stream or see one crawling on land....watch out!!
You've probably never seen one of these creatures, and that's O.K. --they're hard to find. They spend two to four years of their lives in the water living under rocks, like we mentioned above. After spending a few years in a stream they crawl onto land--sometimes several hundred meters from the water--where they pupate. After a week or two they emerge as adults, in much the same way that caterpillars turn into butterflies.
Most people, even those who know about hellgramites, have never seen an adult hellgramite. The adults are known as dobsonflies, because they fly along streams and rivers exclusively at night. They're sometimes attracted to lights, so you might see one flying around a streetlight at night if you're near a stream or river. But don't be afraid, the adults are harmless -- although they are big and look scary!
Class: Insecta
Order: Megaloptera
Family: Corydalidae
Genus: Corydalus
Species: cornutus
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Want to know more about Minnesota's water? Check out our Water page and find out more about the quality of Minnesota's water.
The bug highlighted on this page was collected by MPCA's Water Quality Lab. This lab samples and analyzes water from around Minnesota.