Snowfly: A Winter Stonefly and a request from the Xerces Society

F.Y.I. – StoneFly
March 2, 2010
With the help of your site there is no doubt that what we came across is the StoneFly. This is just additional comments if anyone is interested. While hiking on Feb 28, 2010 with temperatures of about +2 celcius we saw hundreds (or thousands) of these insects slowly crawling across the top of the snow ALL in the same direction (maybe toward the river or bush, which were both in that direction). If we stood still for a few seconds the bugs closest would almost always turn toward us (eek!). We thought maybe they were young Earwigs and it might be a sign of an infestation for the summer but it is nice to see that is not the case. We were very surprised to see any bugs at all!
Thanks for your excellent site!
Southern Ontario, Canada (about 25km n/w of Toronto along the Humber river)


Hi Dan,
Thanks for your wonderful observations of the behavior of the Snowfly, a species of Winter Stonefly.  Can you recall if the alignment had anything to do with the sun or with the wind?  For Americans that might be celcius challenged, +2 translates to about 35 degrees Fahrenheit.  Thanks so much for including the terrain where the sighting occurred.  We are happy to see that there was an instant hit to our Bug of the Month posting for March.

Location: Southern Ontario along the Humber River

It was very overcast for the entire day so that you couldn’t even tell in which direction the sun was. There was no discernable breeze but the flies would have been headed directly into the slight breeze that there was. To me it doesn’t seem like it was either of those factors that effected their direction though.
There would have been 2-3 acres of the flies fairly evenly dispersed and I would say that every one of the flies was headed the same direction. There are a few photos and you can see in the photos with more than one fly that they are all facing the same direction. In their tiny little insect minds it seemed that they knew exactly where they were going….

Request from the Xerces Society
Permission to Use Photo
Hi there; I am conservation biologist with the Xerces Society ( currently writing an Endangered Species Act (ESA) petition to list a couple of rare, endemic, and highly threatened Idaho snowflies (family: Capniidae). I am inquiring after permission to potentially use a photo that a user submitted on your site. Do you have contact information for all of your users? The photo of interest is at this url: 2010/03/02/snowfly-a-winter-stonefly-2/. Posted just yesterday. The photo would be credited, of course.

Hi Sarah,
Here at What’s That Bug? we reserve the right to grant permission to nonprofit education ventures to use images posted to our site, often because the requests are made years after the photos were submitted and we cannot contact the photographer.  In this case, Dan’s email address was still handy, and he can respond directly to you if he would like to grant permission.

Hello Sarah,
Yes, I do give permission to use these photos. If you do use the photo(s) and your report will be accessible to the public I wouldn’t mind knowing how to take a look at it when complete. I have been trying to inspire a teenage niece and nephew to have an interest in photography (I believe an enthusiasm for photography enhances your appreciation for everything you see whether photography related or not) and they may be impressed to see what interesting things can develop. Don’t worry if you forget to inform us when the time comes. It is not terribly important.
I have attached the highest resolution photo of the fly. There are 5 or 6 other photos of groups of flies on the snow if they could be of any use. Let me know if you would like a copy of them.
If these flies are rare enough that there should be some effort to preserve their environment then let me know and I will forward the info to conservation groups here.
It is nice to see that my photos might be of some use!
Good luck with your efforts!

Dear Sarah and Dan,
I am glad to see that we have come to a collaborative agreement in this matter.  Often preservation of a single humble species is imperative for the preservation of an entire ecosystem.

Thank you, Dan.
Yes, I will email you the petition when complete.
For the time being, do introduce your niece and nephew to our website,, which features many fantastic photos as well as lots of really good, free invertebrate conservation resources.
The “store” has some cool kids books for sale, too, if you are interested.
Since your species is unidentified, I have no idea about its rarity. Many snowfly species are weak flyers (hence the walking you observed?) and are highly endemic (e.g. confined to single stream or small cluster of sites). They are also generally very sensitive to pollutants and have very narrow habitat requirements (e.g. cold water, high dissolved oxygen, pebble-gravel substrate, etc.). In fact, stoneflies are considered to be one of the most sensitive indicators of water quality in streams and are frequently used as sentinel organisms in biomonitoring, as they are among the first macroinvertebrates to disappear from systems impacted by physical habitat degradation and thermal and chemical pollution.
Re: your species, I would start by looking on NatureServe (or whatever local Conservation Resources you have) to see if there are any snowfly species in your area that people have already flagged as sensitive. If so, you could do your best at further ID, or follow through with them to see what they think. I might have a chance to look into this a little bit, too, in the coming month or so. Right now I’m rushing to get this petition out in time, or I would do more.
Thanks so much,
I’m really quite envious of your sighting!

Hi again Dan (White),
Sorry, I missed the part about you having photos of multiple stoneflies together.
Yes, those would be really cool to see if you get a chance!
I’m curious about their density while walking, etc.

UPDATE:  June 22, 2010
Hi Dan,
just wanted to let you know that we filed the petition for Capnia lineata and zukeli
It is currently available on the home page of our website ( ), a few items down…
Thanks again for the use of your photo!
It looks great!

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