A caddisfly larval specimen peeking out of its case

Aquatic insects are the best insects

A caddisfly larval specimen peeking out of its case
A tiny caddisfly larval specimen (Order Trichoptera), collected from a stream in Boulder Canyon, Boulder, Colorado, USA, on September 9, 2012.

Let’s just call this Aquatic Insect Month, since I still haven’t gotten back to the Iceland posts. This morning I spent a few hours in lab identifying the aquatic insects I collected in Boulder Canyon back in September for my entomology class, using the excellent key An Illustrated Guide to the Mountain Stream Insects of Colorado, by J. V. Ward, Boris C. Kondratieff, and R. E. Zuellig. Fortunately for my sanity, we only have to identify our specimens to family level (I figure I can always come back to the collection at my leisure after the semester is over).

This was my first time attempting to take photos with the microscope (most of these specimens are only a few millimeters long), so I’m afraid I haven’t quite got the hang of the lighting and focus, but you can still see many of the awesome features of these aquatic larvae.

The caddisfly at the top of the post didn’t seem to be identifiable without removing it from the case, which I didn’t really want to do, but I did have representatives of two more readily identifiable families of caddisflies (Order Trichoptera). The first, which I didn’t photograph, was a humpless casemaker caddisfly in the family Brachycentridae, likely Brachycentrus americanus in this area, which is characterized by a four-sided case. But not all caddisflies form larval cases. Net-spinning caddisflies of the family Hydropsychidae use silk to form “retreats” against rocks, rather than creating a case that they can carry around like the caddisfly above. In addition to providing protection, these nets also trap food for the larva, so these caddisflies require flowing water, such as the mountain stream we collected these from:

Net-spinning caddisfly (Family Hydropsychidae), larva

Sadly, my two tiny mayfly nymph specimens were extremely fragile and ended up broken to varying degrees. This one at least only lost some of its caudal filaments:

Small mayfly (Family Baetidae), nymph

Both of the mayflies I collected were in the family Baetidae, the small mayflies or small minnow mayflies, which are among the smallest mayflies when fully grown. The nymphs feed primarily on algae.

I think the oddest-looking larvae in my collection were the black flies (Family Simuliidae):

Black fly larva (Family Simuliidae), larva

At the top of the picture, you can see the characteristic cerebral fans, foldable fans on the head which the larvae use to gather food such as algae and organic debris. Here’s a sadly not very clear closeup:

Black fly larva (Family Simuliidae), larva

On the hind end, they have a circle of tiny hooks which they use to hold onto the substrate:

Black fly larva (Family Simuliidae), larva

The fuzzy white bit may be the remnants of a silk holdfast, which the larva can use to help hold its place or to move around without being swept away by the current, but it’s hard to tell.

In addition to these, I also had a wonderful large stonefly naiad in the family Perlidae, probably Acroneuria, which was too scrunched up to photograph well, and a tiny riffle beetle (Family Elmidae). I think that’s a pretty impressive assortment for a quick stop!

Many thanks to our TA Tim Szewczyk for confirming my IDs and pointing out baffling characters.

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