Yesterday’s posting about an Orgy in Nelson speculated that the participants were mayflies, and that, owing to their short lives, it was a one-night event. The pictures from the next evening showed I was wrong on the second point, and a couple of people challenged the first, suggesting the insects were really caddisflies.
See the comments, below, where it is finally determined that these insects are caddisflies.
Actually, it dawned on me yesterday, that even if mayflies only lived a few hours, there could be a different batch swarming the following evening, so I took a look and there they were (pictures below).
But, are these mayflies or caddisflies? It seems that both species will do this sort of thing. The only way to be sure is to collect some spent ones on the ground. I failed to find any.
Could one settle the issue from the pictures showing them flying around distant tall trees? Possibly, but to do so unambiguously would require a better camera than I have. At best, about all one might distinguish is the difference in the shape of the wings: a mayfly’s wings are widest near the body (proximal); a caddisfly’s are widest near the tips (distal). With each cover picture, below, I include a detailed shot (full-resolution crop) from a random location within the swarm. Admittedly, there are ambiguities, but it looks as if the wings are widest near the body, and so maybe they are mayflies. But, the jury is out.
Either way around, being in a swarm enables them to spend their short adult lives mating.
The ability to even see the swarm strongly depends upon the lighting and the background. When this same group of insects was seen against the sky rather than the mountain, they seemed to vanish.
In a detail of a random portion of the above picture, wing shapes are sometimes evident.
Another tree and another image followed by a detail.
Finally, a pair of backlit pictures (shot in the general direction of the Sun).
National Geographic-worthy captures in my humble opinion. Best regards, ~Scott
Arlene Anderson sent me this picture of one a number of the insects that landed at her home in Nelson after swarming around adjacent trees. It is not a mayfly, but probably a caddisfly. Does anyone know?
Hi Alistair,
At first look, the picture from Arlene appears to be a moth of some type, although moths and caddiflies share a number of features that can make photo-based ID difficult. It would be nice to have a side shot of the critter – adult caddisflies hold their wings tent-like over the body, rather than more flattened as many moths do. Given the time of year and the mass emergence that you’ve experienced in the WK, my best guess on Arlene’s insect is would be caddisfly.
Hi Alistair,
More thoughts on the fascinating phenomenon of the swarming insects you photographed recently. The insects in the pictures you sent are definitely dead caddisflies. I have never seen moths congregate in the manner that adult caddisflies do. When I lived in Castlegar, the caddisflies would gather around tall trees in cloud-like fashion – perhaps using the trees as resting places and/or landmarks. The swarming behaviour is what I saw each year with the caddisflies or “river moths” – as many people like to call them – that emerged from the Columbia River in Castlegar. The timing for a large caddisfly emergence makes sense, too – the adult caddisflies were typically found in great abundance in early to mid-July when I lived there.
The pesky little creatures that congregate along the river banks in Castlegar appear to be Caddis flies. People these days generally call them River Moths although it seems back in the 70s a common term was Shad Flies. The swarms of these creatures are amazingly thick in the Thrums and Castlegar area, but their proliferation extends down to Trail and even well away from the Kootenay and Columbia Rivers to places like the Krestova end of the Pass Creek valley.
It seems that an extended period of really hot weather increases their numbers. At the height of their breeding season drivers find the front of their vehicle coated with the dead insects — from the headlights, to the windsheild, and all front facing surfaces. The rock cut on the Castlegar end of Thrums is one spot where cars meet many River Moths.
At homes where the Caddisflies mass in the dark, the outside surfaces of windows draw the River Moths as they try to get closer to the light inside. Porch lights have to be left off at this time of the year but even so, any time a door is opened some enter the home. They are also very good at finding rips in window screens that allow thenm to gain access into houses or even small openings that allow them to get into outdoor light fixtures to get closer to the light bulb.
They are very annoying but luckily they don’t bite.
I’ve seen the swarms in the setting sunlight above the treetops near the Brilliant Bridge (like in the photos in the links posted by Ruth). I’m not sure if that’s what you were seeing in Nelson. It could be a different creature. The Castlegar swarms appear dark while what you captured in photos look white.
I travel around the area a fair bit and go for walks all over. I don’t remember seeing any River Moths in Nelson. I have seen swarms of another fly in the Trail area. Those flies are smaller with a white body and sort of greenish translucent wings. They find shady areas not far from the river to stay out of the direct sunshine. Walking through the bush I disturbed them and they swarmed aound in clouds. It made breathing difficult as I tried to avoid breathing these little creatures in. I’ve seen these same flies in another area away from Trail but right now I can’t remember where it was. It may have been Nelson.
I spent some time searching the internet for information on the Caddis Fly in Castlegar. The pictures I found of Mayflies and Shad flies look very different tham the Caddisflies in Castlegar. Here’s a few interesting links:
Fly Fishing Caddis & Sedges
http://flyguys.net/aquatic-entomology/fly-fishing-caddis-sedges
Fly Fishing the Mayfly
http://flyguys.net/aquatic-entomology/fly-fishing-mayfly
CADDISFLY (Sedge)
article by Ron Newman
Scientific Name:
Class – Insecta. Order – Trichoptera (Hair Wing). Family – Limnephilidae
http://www.bcadventure.com/adventure/angling/bugs/caddisfly/caddisfly.phtml
Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
Order Trichoptera – Caddisflies
http://bugguide.net/node/view/5233/bgimage
LimnephilidaeFrom Wikipedia, the free encyclopedia
http://en.wikipedia.org/wiki/Limnephilidae
It’s very interesting how some fly-fishers use minutely detailed information to tie just the right fly for catching the fish they are after.