Northern Caddisfly Adult

2008 November 22

Back in April, I had pictures of a caddisfly larva that we found in the little stream out back. Since then, I’d been wanting to get pictures of an adult too, but I wasn’t quite sure what time of year the local species emerged. Well, wonder no more: here are the adults, which started coming to our porch light right around the middle of October, and last I checked (November 14, after we’d had one significant snowfall) they were still around. They look a lot like moths, but aren’t.

I tried to get pictures of them while they were alive at first, but they didn’t come out quite as clear as I might have liked[1].

So, I ended up re-photographing them after they had died, so that they would lie flat and hold still for more detailed photography:

While the clarity is a lot better, and we can see the wing venation pretty well, this does point up one of the problems with dead specimens – they get brittle, and appendages tend to break off[2]. The one above looks like it has short antennae, but that was because they snapped off when I dropped it onto the graph paper. Luckily I had two of them, and you can see the broken antennae of the first specimen laying here beside the second specimen:

The most likely match I can find on Bug Guide is one of the Northern Caddisflies, Frenesia missa. Other people are reporting these to be out and about in October, November, and even as late as December.

The only economic impact of caddisflies is evidently that they are food for fish, so most of the information about them is on fly-fishing sites. The basic lifecycle goes like this:
1. Egg hatches in a slow-moving stream
2. Larva builds a shelter, usually a tube of sticks, sand, or whatever is characteristic for their species
3. Larva eats bits of food that drift by, goes through five molts
4. Larva closes itself into its shelter and pupates
5. When the pupa is mature, it crawls out of the case and swims to the surface. An odd feature here is that caddisfly pupae are not the nearly-featureless ovoids that you kind of expect from a pupa. No, these have legs, and can swim and crawl.
6. The pupa hauls itself out of the water, and the adult emerges to fly off and mate
7. The adult mates and lays eggs. While they don’t live for a super-long time, they aren’t as bad off as mayflies that die after about a day. Adult caddisflies can evidently last up to a few weeks, at least in the species that can eat nectar to keep themselves going.

The way caddisflies are drawn to lights, it is easy to mistake them for moths. The giveaways are first, that they have long, thin antennae, while most moths have feathery antennae. Second, their wings are not covered with powdery scales like moth wings are. Instead, they are membranous wings, with short hairs over the surface and at the edges, like this:

I’m not sure how far they generally fly from their home streams. Probably not too far, because there isn’t a lot of percentage in mating only to find that you are too far away from any streams to get to one to lay eggs. But, they do certainly go far enough to be able to colonize new streams. We certainly had a lot of them at our porch light[5], and some of them were even mating there, but since the little stream out back is only about 50 feet from the house, they obviously didn’t have to go very far.
[1] I finally broke down and got an actual purpose-made macro lens, for things that are too small for the unassisted camera, but too big or too 3-dimensional for the improvised high-power macro I’ve been using. I ended up buying a Raynox DCR-150, which I think is a very nice piece of optics [4]. It comes with a universal mount that lets you clip it onto pretty much any camera that has threads on the lens for mounting filters. When you look through it, there are none of the aberrations that you normally get with a magnifying glass and that are the giveaway that you are using one. It just makes the world look, well, bigger. It’s no blame to the lens that I didn’t do better here, it just needs different camera settings and different procedures than the other lens, and I haven’t worked out the best way to make use of it yet. In particular, I need to come up with some sort of mount that will hold it as steady as the microscope frame that I usually use, while still allowing me to make side shots as well as straight-up-and-down shots.

[2] A story I read a while back: in an introductory entomology course, one of the exam questions was “How many legs does a crane fly have?”[3] One answer was, “Between 1 and 4, based on the specimens in our teaching collection”.

[3] The right answer is supposed to be “6”

[4] Raynox also makes the DCR-250, which is more powerful than the DCR-150 but has less depth of field. I considered getting the DCR-250, but overall it has about the same capabilities as my first macro lens, and would have left me with some of the same limitations. I may end up getting one of them too at some point, though, if only because it looks better suited for taking pictures outdoors instead of on my microscope stage.

[5] There are a lot of kinds of insects that are drawn to lights at night, and just about as many “explanations” of why they do it. I don’t know which explanation (if any) is correct, they range from insects thinking the light is the moon and trying to use it to navigate, to having the light-sensing cells in their eyes overloaded from the bright light so that they think that “bright” is actually “dark”. One thing to keep in mind, though, is that whatever the explanation is, it must be something that will apply to a very broad range of insect species[6]. That’s why I doubt the “moon navigation” explanation, that sounds like something that only a few fairly specialized insects would do. Instead, we have a whole bunch of tenuously-related insects (antlions, moths, caddisflies, and many others) all doing it.

[6] Not all night-flying insects are drawn to lights, though. Notably, mosquitos and black flies are not drawn by lights to any great extent. Which is why those electronic bug-zappers that use lights for lures are useless – all they do is fry a bunch of pretty harmless insects, while the biting flies and mosquitos that they are intended to kill pretty much just ignore them. If you want to trap mosquitos, you need one of the chemical lure units. Those work, although they are generally kind of pricey and the unit we bought became rather fussy to get started once it was more than a year old.

One Response
  1. Carla permalink
    November 26, 2009

    awesome pictures! the one of the wing is great because you can actually see the hairs which are characteristic of the Trichoptera Order of Insects! thank you!

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