Bugging You From San Juan Island

Here’s a unique specimen I have to show you. I found this fly on Wednesday after lunch when I went to look for a different species of fly around our above ground pool. I was actually looking for Woodpecker Flies when I found this one. Since I’ve committed to doing a presentation about them for the Scarab Society in September, I’m hoping to observe these weird Woodpecker flies again in the wild and take additional photos and videos to add to what I have collected already.

I didn’t expect to see anything IN the pool. Mostly, I was looking at vertical surfaces, like the sides of the pool and the sides of a nearby tree. When I glanced across the surface of the water, this little one stood out right away. I got a paper bowl to gently scoop it out, expecting it was deceased. It surprised me when it moved just a bit, then wiggled and flipped off the bowl onto the ground.

I bent down to inspect it, and when I touched it, it flipped around again like a fish out of water. Strange.

I had a plastic cup, so I managed to recapture the fly, wet and bedraggled as it was. I took it back into the house long enough for me to get my other camera. The lighting was better outside, so back out we went.

In case you are wondering, this is one of the Picture Wing Flies in the family Tephrididae. Also known as Fruit Flies. “Picture” references the patterned spots or stripes on the wings. There are other flies, like Drosophila sp., called fruit flies that aren’t actually fruit flies at all. THIS is a true fruit fly.

Many species of fruit flies are known for their pest status, however, there are over 4,300 described species in this family and the great majority of them are not pestiferous at all. They are merely a part of the local, natural ecosystem at large.

I used a key and geographic distribution records to determine the species for this one and believe it to be Chetostoma californicum. Trying to find host plant information led to me to do some deeper digging and to actually order a few more reference books on Tephridid flies. I have another fruit fly specimen I found when we were in Mexico, and plan to share that one with you next Friday. As I learn more about this particular one though, I will update my blog post accordingly.

The reference material I did find about Chetostoma californicum was largely from California and Arizona. Inferring from the documented host plant relationships recorded, it is likely one relationship possible in our immediate area is with native honeysuckle (Lonicera sp.). I also read adults of this species have been collected from Pines (Pinus sp.). We have a Pine tree just next to our above ground pool where the fly was collected.

Geographic distribution records for this fly include Western North America, primarily coastal, down to CA and into Arizona. You can view the GBIF map of reported sightings here – https://www.gbif.org/species/1623842 and also search for observations of the species posted on iNaturalist https://www.inaturalist.org/observations?subview=map&taxon_id=335747

The only additional personal record I have of this fly on San Juan Island is from February 16, 2024. I would conclude, based on my own observations, that this fly is not particularly an abundant species here. In checking for reports of the species on San Juan, my two posted observations are two of three total for the county.

Now if I can just find out what’s behind the fish flippy behavior…..stay tuned!

Thanks for reading.

References

No author. 2026. Chetostoma californicum. Grokipedia. https://grokipedia.com/page/chetostoma_californicum

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

Foote, R.H. and Blanc. F.L. 1963. The Fruit Flies or Tephritidae of California. Bulletin of the California Insect Survey. University of California Press. Berkeley and Los Angeles. https://essig.berkeley.edu/documents/cis/cis07.pdf

LeBlanc, 1959. A new species of Chaetostoma from California (Diptera: Tephritidae). Pan-Pacific Entomologist. 35:201-204. https://biostor.org/reference/225819

Wasbauer MS. 1972. An annotated host catalog of the fruit flies of America north of
Mexico (Diptera: Tephritidae). Occas. Pap. Calif. Dep. Agric. Bur. Entomol. 19:1–172.