Nothing to do with fish

Spring Fishfly - male

The weather was so warm while I was at my parents’, I couldn’t resist setting up to try to catch a few moths, even though it was a bit breezy and they were calling for rain in the early morning. Since I’m not living there, I have to take advantage of whatever opportunity I have during visits, and can’t be as choosy about the weather. I set up two sheets with blacklights, one near the house and one along the driveway about 100 metres/yards away. I also ran the trap overnight, just putting a glass bowl over the bulb to protect it from the rain that was supposed to arrive. I was hopeful for a few moths flying despite the breeze, and wasn’t disappointed. I ended up with somewhere between 80 and 90 species that evening – double the highest count I’d had there before, and more than enough to keep me occupied for hours photographing all the species new to me (which was most of them) the next day, even if it wasn’t quite up to par with TheMothMan’s 130 species he picked up at Rondeau earlier that week.

As observed in my post about the Giant Water Bug, the lights don’t attract just moths. You can get a good variety of insects, including many species of beetle, flies, midges, ichnumonid wasps, and others. Among the “others” I discovered a number of these guys. This is a fishfly, from the genus Chauliodes. I spent some time puzzling over the two different species on, and finally decided that this was the Spring Fishfly, C. rastricornis. The most obvious difference I noted from the photos is that at the back of the head there’s two short dashes side-by-side, and in the Spring Fishfly they are dark-on-light, while in the Summer Fishfly (C. pectinicornis), they are light-on-dark. Time of year can also help, but we’re at the time where they start overlapping a bit so it wasn’t of much use to me. Both species are found through most of eastern North America.

Spring Fishfly - female

Males and females are dimorphic. The females are larger, and have straight, thin antennae, while the smaller males have feathery (pectinate) antennae. Like with moths, the males use these feathery antennae for detecting the pheromones of the females. I got both males and females in to the sheets and in the moth trap, perhaps half a dozen individuals total, though unfortunately the female I caught for a photo didn’t want to cooperate for me, so this was the best photo I got of her. Both sexes are quite large, easily a couple inches long. The first one I got in to the sheet quite startled me, because of its size and ferocious look.

Spring Fishfly - male

They spend most of their life cycle in the water or associated with it. Eggs are laid on vegetation near the water’s edge, and when the larvae hatch they crawl to the water where they can spend as much as two to three years. During that time they’re omnivorous – they’ll eat a lot of detritus, but also graze on the vegetation or opportunistically predate other invertebrates. Because of these feeding habits they prefer still water bodies with a good layer of detritus on the bottom. When they’re ready to pupate, the larvae leave the water again, finding a rotting log or dead tree where they pupate under the bark. The adults emerge after about 10 days, and will live for about a week to mate and lay eggs.

Spring Fishfly - male

Supposedly the fishflies don’t eat while adults, so I’m not sure what these things that look like mandibles are, or are for. Fishflies resemble the related dobsonflies, except that the dobsonflies have huge mandibles. I also don’t know what the purpose of the dobsonfly’s mandibles are, as they don’t eat as adults, either. In fact, there’s very little detailed information on fishflies, and it’s compounded by the fact that mayflies, those ephemeral insects that line the screen door and exterior walls of the cottage by the hundreds in the summer, are also known as “fishflies” in some areas. There’s also another genus of fishfly, Nigronia, which are more darkly patterened than the Chauliodes. I don’t know where the name “fishfly” comes from, as I don’t think any life stage of any of the species actually has anything to do with fish. However, the larvae of fishflies and dobsonflies are often used as bait for fly fishing…

Spring Fishfly - male

Although none of the references I looked at mention it, the adult fishflies have large compound eyes and therefore, I presume, excellent sight. Given that they don’t eat as adults, I assume it’s primarily used in locating mates and avoiding predators. There’s also three shiny bumps on its head between its antennae, which are ocelli, light-detecting organs that sense light and dark, but not detail the way the compound eye can. Ocelli are usually unable to perceive form, but are much more sensitive to light, and process information more quickly, than compound eyes. Ocelli are divided into two main types: dorsal (such as these) and lateral (on the sides). Dorsal ocelli are found especially on flying insects, where they use the light sensors to help orient themselves vertically while flying.


Author: Seabrooke

Author of Peterson Field Guide to Moths. #WriteOnCon Mastermind. Writer of action/thriller SF/F YA. Story junkie. Nature nut. Tea addict. Mother. Finding happiness in the little things. Twitter: @SeabrookeN / @SeabrookeLeckie

12 thoughts on “Nothing to do with fish”

  1. Those wings are quite lovely, seen close up. The face, however, only a mother could love! : )
    The scientific name of the order, megaloptera, if from the Greek for large or giant, and wings. The larvae of dobsonflies and fishflies are called hellgrammites. They are the largest of aquatic insects.
    The large jaws may play a role in mating. Dobsonfly males have been observed to place their jaws on top of the wings of the female during mating (Voshell-Freshwater Invertebrates of NA).

  2. Wow, what great macro shots. I’m very impressed with your talent and you must of had a very cooperative fishfly to work with. I used to catch and fish with helgramites and just posted about it in a river post.

  3. A two-inch insect and there’s no information about it???!!! This one’s brand-new to me; gotta keep an eye open for it now.

  4. Thanks for the additional info, Horsin’around. Sometimes printed references are much more useful!

    Thanks, Fishing Guy. I must say the male, at least, was a pretty cooperative individual.

    I’d never seen these guys till now either, Lavenderbay. They seem to stick pretty close to water – except when attracted to light.

  5. I was under the impression that and adult fish fly did eat, while adult dobson’s didn’t? I could be mistaken. And yes it is believed that the large jaws of the male dobson are used for mating purposes.

  6. Hi, your webpage was just the answer my 7th grade daughter needed to identify a catch for her insect collection project. We caught a male Summer Fishfly in Dunn, NC and we live no where near a shoreline. Very interesting.

  7. Excellent description of the compound eyes and ocelli. I was wondering what the three simple eyes between the large compound eyes were for. Great pictures that confirmed the ID of the fishfly that I photographed.

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