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Artistic view of a Male Pteronarcys californica (Pteronarcyidae) (Giant Salmonfly) Stonefly Adult from the Gallatin River in Montana
Pteronarcys californica

The giant Salmonflies of the Western mountains are legendary for their proclivity to elicit consistent dry-fly action and ferocious strikes.

Lateral view of a Female Sweltsa borealis (Chloroperlidae) (Boreal Sallfly) Stonefly Adult from Harris Creek in Washington
I was not fishing, but happened to be at an unrelated social event on a hill above this tiny creek (which I never even saw) when this stonefly flew by me. I assume it came from there. Some key characteristics are tricky to follow, but process of elimination ultimately led me to Sweltsa borealis. It is reassuringly similar to this specimen posted by Bob Newell years ago. It is also so strikingly similar to this nymph from the same river system that I'm comfortable identifying that nymph from this adult. I was especially pleased with the closeup photo of four mites parasitizing this one.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Insect Family Corydalidae (Hellgrammites)

Hellgrammites are the vicious larvae of the Dobsonflies, some of the only trout stream insects which pose a biting threat to the angler. The pincers of the adult are even more frightening that the larva's, and they're aggressive enough to use them once in a while.

This family's life cycle does not create good dry fly opportunities, but the larvae may be eaten by trout year-round. They are a secret told only by stomach samples of well-fed trout.

Where & when

In 1001 records from GBIF, adults of this family have mostly been collected during July (22%), June (21%), May (15%), August (13%), September (7%), and April (6%).

In 165 records from GBIF, this family has been collected at elevations ranging from 3 to 12631 ft, with an average (median) of 2510 ft.

Family Range

Hatching behavior

The larvae exit the stream to pupate in burrows in the ground, so their emergence is completely unimportant to trout.

Egg-Laying behavior

Egg-laying dobsonfly adults are never, in my experience, common enough on trout streams to cause any sort of rise, but they are the sort of huge meaty insect that trout are unlikely ot pass up.

Larva & pupa biology

I do not know how hellgrammites become available to trout, exactly -- perhaps by accident and perhaps they undergo behavioral drift. They are such large insects and they show up in trout diets often enough that imitations make good searching patterns. In fact, the infamous wooly bugger and wooly worm fly patterns probably owe some of their success to their similarity to hellgrammites.

Specimens of Hellgrammites:

1 Male Adult
1 Female Adult
7 Larvae

Discussions of Corydalidae

Best time of year to harvest hellgramites
13 replies
Posted by Rblouser on Jun 27, 2008
Last reply on Jun 11, 2019 by Sapperstyle
I have just recently started fishing with hellgies and need some info on the best time of year for catching, bait. Any insight will be greatly appreciated
Dobson Fly
26 replies
Posted by Jesse on Jun 23, 2011 in the genus Corydalus
Last reply on Sep 12, 2013 by PaulRoberts
What can anyone tell me about the Dobson Fly?

(General now guys, we don't have to go all scientific with it ha)!
Anyone have hellgrammite experiences to share?
56 replies
Posted by Troutnut on Nov 18, 2006
Last reply on Aug 23, 2013 by Trout_House
I'm working on a magazine article about hellgrammites, which I think are a generally underrated food source and an extremely cool group of insects.

I'm going to do a lot of research and combine it with my own experiences, but many of you have been fly fishing longer than I've been alive, so I'd like to see if any of you have stories about them -- catching big trout with stomachs full of them, finding trout rising to the dobsonfly adults, getting bit by these bugs, or anything else.
Fishfly is not a hellgramite
5 replies
Posted by Ofieldstrea on Jun 24, 2007 in the genus Nigronia
Last reply on Jun 28, 2011 by PaulRoberts
Troutnut ... the term "hellgramite" is reserved for the Dobsonfly (Corydalinae). Though the Fishfly (Chauliodinae) and the dobsonfly are from the same Megaloptera family, at first glance appear similar, and have similar stages of development, they are from different subfamily with differing subspecies and have very different morphology and biology.

The dobsonfly inhabit the more oxygenated waters of riffles and possess only tuffed gills for respiration. The fishfly inhabit the quiter waters of pools and still water. Fishflies have a primative gills called lateral filaments, while some species of fishfly utilize breathing tubes, located posterior, to accomodate the use of atmospheric oxygen for breathing in low dissolved oxygen envirions while remaining submerged.

So .. it is incorrect to use the term 'hellgramite' when talking about the fishfly larvae. They are simply, 'fishfly larvae'. You really should change your reference.

---- Reference -----
McCafferty, W. Patrick, 1981. Aquatic Entomology; Chpt. 11, Fishflies, Dobsonflies and Alderflies (order Megaloptera), p. 189-196

trying to figure out
1 replies
Posted by Buggy on Apr 19, 2009
Last reply on Apr 19, 2009 by GONZO
I am from ontario canada and i pick hellgrammites for a local bait shop owner i was just wondering when is the earliest i could start picking...last year i started in june but i hear you can start sooner when is the earliest i can do this??? thanks for your help

serious picker

Start a Discussion of Corydalidae


Insect Family Corydalidae (Hellgrammites)

Genus in Corydalidae: Chauliodes, Corydalus, Nigronia
4 genera (Dysmicohermes, Neohermes, Orohermes, and Protochauliodes) aren't included.
Family Range
Common Name
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