Subject: What is this?
Location: Calgary Alberta Canada
June 20, 2016 9:10 pm
Hi, I live in Calgary Alberta Canada and now noticed the follow fly, which generally appears in swarms around the house or spruce trees. Flies are out from June to August/September. The only come out I the late afternoon or evening when the temperature begins to cool. During the day they rest on the side of the house or along the soffits. House backs onto a green space and is roughly 100 yards from the bow river. Swarms have become larger in recent years and I’d love to know what they are. They do not bite or sting. Just very annoying and unsightly.
Thanks for your help!
This is a Caddisfly, a member of the order Trichoptera. Caddisflies are often described as “mothlike” and the fact that you are so close to the river explains why you have so many Caddisflies in your yard. Immature Caddisflies, sometimes called Caseworms, are aquatic, frequently used as live bait by anglers, and according to BugGuide: “Most caddisfly larvae are intolerant of pollution; therefore, their presence is an indication of good water quality, and their absence in areas where they previously occurred may be an indication of polluted water.” Caseworms make cases from a variety of materials, including sticks, sand, pebbles, snail shells, bits of leaves and many other materials, however, each species is very specific about the material used and the shape of the case. BugGuide also notes: “Adults rest on nearby vegetation during the day; flight activity begins at dusk. Adults are attracted – sometimes in great numbers – to artificial light” and that agrees perfectly with your account. More information on Caddisflies can be found on Aquatax where it states: “Probably the most interesting feature to the non-fishing general public regarding this group is the cases that many of the larvae construct out of various materials. Caddisflies are found in all types of aquatic habitats throughout Saskatchewan. The majority are intolerant of pollution and, as such, are valuable tools for monitoring organic and chemical contamination of habitats.”