Asilidae | Bugging You From San Juan Island

Identifying the Nicocles canadensis Robber Fly

Posted on June 17, 2025 by "BUGGING" YOU FROM San Juan Island Leave a comment

It has taken a bit of time to finally sort out genus and species for this very cool Robber fly with beautiful caramel-brown mottled wings I spied the evening of June 6, 2025. It perched on a dried apple mint stem from last season, no doubt scouting the terrain to see what might be on the menu for dinner. Robber flies (Family Asilidae) are predatory. They catch other small invertebrates to eat, paralyzing them with special salivary digestive enzymes and then sucking up the liquified contents through the proboscis (Cannings, 2013).

Getting to an identification beyond Genus for this one has been incredibly frustrating, and complicating the process is the limitation of the key I was using (Wilcox, 1946), which primarily describes male specimens.

Robert Cannings has studied the Asilidae for many years in British Columbia and states this genus “sorely requires systematic attention.” I finally just gave up and reached out to Rob for help. He wrote me and said, “I’m pretty sure this is Nicocles canadensis. It’s a female, and some females are difficult, even when under a scope, because the Wilcox key, which is the best we have for now, deals with them poorly and concentrates on males. Nicocles canadensis is the species in the genus most often seen on BC’s south coast and, I assume, in your area.”

This is the only Nicocles fly I’ve ever found on our property on San Juan. According to Rob’s 2014 publication (linked in the references below) in Canada, ” Nicocles canadensis is restricted to Garry oak savanna and adjacent dry woodland on southern Vancouver Island (Saanich is the type locality),” so I anticipate this may be similar for our neighboring area.

Check out the attached references if you are interested in learning more about Robber Flies in our region.

Thanks for reading!

References

Cannings, R.A. 2014. The Robber Flies (Diptera: Asilidae) of Western Canadian Grasslands. 10.3752/9780968932179.ch7. https://www.researchgate.net/publication/268524943_The_Robber_Flies_Diptera_Asilidae_of_Western_Canadian_Grasslands

Cannings, R.A. 2013. Robber Flies (INSECTA: DIPTERA: ASILIDAE) Of The Montane Cordillera Ecozone.

Cannings, R.A. 1994. Robber Flies (Diptera: Asilidae) new to Canada, British Columbia, Yukon,
and the Northwest Territories with notes on distribution and habitat. J. Entomol. Soc.
British Columbia: 91: 19-26. https://www.biodiversitylibrary.org/part/213777

Cole, F. R. 1969. The Flies of Western North America. University of California Press. Berkeley and Los Angeles.

Fisher, E.M., and Wilcox, J. 1997. Catalogue of the robber flies (Diptera: Asilidae) of the
Nearctic Region. Unpublished preliminary draft.https://staff.royalbcmuseum.bc.ca/wp-content/uploads/2013/08/Catalog-Nearctic-Fisher-Wilcox-1997-manuscript-copy.pdf

Geller-Grimm, F. 2008. Robber Flies (Asilidae). Internet site at http://www.geller-grimm.de/asilidae.htm

Melander, A.L. (1924) Studies in Asilidae (Diptera). Psyche [1923] 30: 207-19. https://onlinelibrary.wiley.com/doi/pdf/10.1155/1923/83461

Wilcox, J. 1946. New Nicocles with a key to the species (Diptera, Asilidae). Bulletin of the Brooklyn Entomological Society 40 (1945): 161-165; New York – Lancaster. https://www.biodiversitylibrary.org/page/50573094#page/180/mode/1up

Know Your Pest Predators – Make Friends with Eudioctria sackeni

Posted on July 11, 2024 by "BUGGING" YOU FROM San Juan Island One comment

This is one of my favorite garden residents (Eudioctria sackeni), or the Sacken Longhorn Robber. I remember the first time I saw one of these, I thought, “Wow, it’s an Ombre Fly!” If you didn’t know, “ombre” means the blending of one particular color hue to another, often from light tints to dark. The coloration in this particular fly is distinctly “ombre,” though it varies in individuals within the species.

Eudioctria flies are in the family group, Asilidae or Robber flies. They are voracious predators of small insects that can be pests of gardens and orchards. Here, you see this one enjoying a small dipteran (fly) of some variety, perched on the leaf of one of my mint plants. The mint is a popular scouting platform. On any given day in the summer, I’ll see 4 or 5 of these flies in a six foot strip of mint which has become quite abundant in the yard over the past few years. The mint seems to be quite attractive to pollinators, and it also provides shelter for other bugs and critters. Our little tree frogs love to sit in the mint too.