Wednesday, July 13, 2011
The "Needle in the Haystack": A "Long-horned" Case-maker
This was a bonus today -- though I've been hoping to find some. That little insect sticking its head out of the case that's attached to that piece of vegetation is a Leptocerid caddisfly larva -- a "Long-horned" case-maker. I'm pretty sure the genus is Nectopsyche (see the entry of 1/26 on Leptocerids)-- but I couldn't get it out of its case, so I can't really confirm that. If you can't see the larva, here's an annotated version of the picture above (and I encourage you to click on the photo to enlarge it.)
I usually find these in the Rivanna, and that's where I went this morning -- to the boat put-in below the bridge at Milton. But, these are extremely hard to find, and it is indeed like looking for a needle in a haystack. Leptocerids -- this genus at least -- attach their cases to the grass or algae that covers the rocks in the Rivanna each summer. This vegetation is long (2-3"), dense, and gnarly. And these cases are tiny -- you'd never see them if you didn't know what to look for. Here's another shot of this insect.
I hope to find more of these throughout the summer (and I should) -- and with luck I'll find some that are a bit bigger than this one!
But I found other treasures today. Such as....
...this beautiful Emerald Dragonfly (family Corduliidae). In Voshell (Freshwater Invertebrates), this would be called a "Skimmer Dragonfly" (pp. 126-127), for which he gives the family name Libellulidae. But Libellulidae and Corduliidae as dragonfly families can be distinguished: in nymphs of the family Libellulidae, the "crenulations on the distal margin of the palpal lobes are usually separated by shallow notches (Merritt, Cummins, and Berg, Aquatic Insects of North America, p. 249), while with those of the Corduliidae family the crenulations are separated by deep notches (same source, p. 246). Here's a microscope view of the notches in question -- and they're deep. (The definition of "deep" is "one-fourth to one-half as high as long" (same source, p. 246).
Some other treats -- damselfly nymphs, both broad-winged and narrow-winged, so a good chance to see how different they are in appearance.
and Narrow-winged (Coenagrionidae)
It's not very difficult to tell them apart. Note the difference in the antennae. With Calopterygidae, the first segment of each antenna is longer than the other segments combined.
One more treat -- a "baby" Hellgrammite. This one was really, really, small -- about 1/8" long. It has not been here in this world very long.
If there's any doubt about the identification, you simply have to look at the anal prolegs: each proleg has two claws at the end. And here is a microscope photo of that. (Oh. Stream monitors should know that when hellgrammites are this small, they can be confused with netspinners. If they look a little bit off, be sure to look at them with a loupe.)
(Below -- another look at our Emerald Dragonfly.)