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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.

Case view of a Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
It's only barely visible in one of my pictures, but I confirmed under the microscope that this one has a prosternal horn and the antennae are mid-way between the eyes and front of the head capsule.

I'm calling this one Pycnopsyche, but it's a bit perplexing. It seems to key definitively to at least Couplet 8 of the Key to Genera of Limnephilidae Larvae. That narrows it down to three genera, and the case seems wrong for the other two. The case looks right for Pycnopsyche, and it fits one of the key characteristics: "Abdominal sternum II without chloride epithelium and abdominal segment IX with only single seta on each side of dorsal sclerite." However, the characteristic "metanotal sa1 sclerites not fused, although often contiguous" does not seem to fit well. Those sclerites sure look fused to me, although I can make out a thin groove in the touching halves in the anterior half under the microscope. Perhaps this is a regional variation.

The only species of Pycnopsyche documented in Washington state is Pycnopsyche guttifera, and the colors and markings around the head of this specimen seem to match very well a specimen of that species from Massachusetts on Bugguide. So I am placing it in that species for now.

Whatever species this is, I photographed another specimen of seemingly the same species from the same spot a couple months later.
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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Mayfly Family Baetiscidae (Armored Mayflies)

The mayflies of this family are known mostly for their curious shapes, but they can create excellent spinner falls, too. Read about Baetisca, the only genus in this family, for details.

Where & when

In 35 records from GBIF, adults of this family have mostly been collected during June (31%), May (23%), April (17%), July (11%), August (9%), and March (6%).

In 17 records from GBIF, this family has been collected at elevations ranging from 3 to 2625 ft, with an average (median) of 2152 ft.

Family Range


To determine whether a specimen of Ephemeroptera belongs to Baetiscidae, use the Key to Families of Mayfly Nymphs or Key to Families of Mayfly Duns and Spinners.

Specimens of the Mayfly Family Baetiscidae

2 Male Duns
2 Female Duns
2 Male Spinners
2 Female Spinners
15 Nymphs

1 Underwater Picture of Baetiscidae Mayflies:

Discussions of Baetiscidae

An important hatch
2 replies
Posted by Troutnut on Jun 26, 2006 in the species Baetisca laurentina
Last reply on Apr 8, 2013 by Willy
Based on reports from several sources and my own experiences, I'm beginning to think it is significantly more important than it has been credited for. The duns emerge by crawling out onto land, so they aren't important, but some of my most memorable fishing nights of 2005 were due to Baetisca spinner falls.

It is a tricky hatch to detect. I haven't seen more than a couple of their spinners in the air at a time, though some of my friends report spotting their swarms. Normally for me they just showed up on the water from unseen swarms upstream. They were mixed with spinners from Ephemerella invaria and Maccaffertium vicarium, among others, but the fish were relentlessly selective to the Baetisca laurentina spinners.

I wasted the better part of an hour flinging a sulphur imitation the first time I encountered a Baetisca fall. Like Ephemerella spinners, they can be hard to spot on the water, and they were much more sparse. I finally captured one, noticed the very different body profile, and since I didn't have anything remotely imitating it I continued to catch no fish. I returned the next night with an imitation with a robust, opaque body, and the fish went crazy for it.

I just finished reading through the account by Caucci and Nastasi in Hatches II about how the extremely important Ephemerella invaria sulphur species went unnoticed for decades because it was confused with Ephemerella dorothea. The maddening difficulty of some dorothea hatches was partially explained away once people understood this difference.

Although Baetisca is much less prominent than Ephemerella invaria, I suspect it has similarly been confused with well-known sulphur species in the rare locations and occasions where it is important.
Baetisca in Vermont
1 replies
Posted by BRAT on Oct 25, 2009 in the genus Baetisca
Last reply on Oct 25, 2009 by Taxon
Hi there; I just gathered a sample from our local Black River here in SE Vermont, and found a thriving population of armored mayflies. Wasn't sure what they were at first, with their bubble-humped backs and short little tails, but once I used my hand lens I realized they have tiny little "thorns" behind their last legs. Their mottled coloring resembles everything I've seen here, confirming my ID. I'll be sending off a sample to a friendly bug lab to let the pros look at them.
6 replies
Posted by Tnoetzel on Jan 14, 2009
Last reply on Jan 28, 2009 by Martinlf
are these flies the flies we call batflies? They look like a size 12 may fly on the water but have a very stubby abreviated and robust body. They are becoming more and more a factor where I fish on the Au Sable River. Do these spinners retract thier tail section into the thorax?
Similiar found in Minnesota
1 replies
Posted by PRohlfsen on May 11, 2007 in the species Baetisca obesa
Last reply on May 11, 2007 by Troutnut
I was fishing the Vermillion River in Minnesota south of the metro area and found a nymph similar to the Armored Mayfly Nymph. It did appear to be much more green in color. It was moving through a really muddy part of the stream, which I found interesting.
Can't wait to hit this hatch
Posted by Troutnut on Jun 12, 2006 in the species Baetisca laurentina
Last reply on Jun 12, 2006 by Troutnut
It sounds like the Baetisca hatch is really going on here in northern Wisconsin now. I've heard reports from more than one source about fishable Baetisca laurentina hatches on two of my favorite rivers. I bought some imitations and hopefully I'll be using them tomorrow!

Start a Discussion of Baetiscidae


Mayfly Family Baetiscidae (Armored Mayflies)

Genus in Baetiscidae
Genus in Baetiscidae: Baetisca
Family Range
Common Name
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