I am not positive that this Syrphid fly is Chrysotoxum flavifrons. The fact that the last segment of the antenna (flagella) is longer than the first two segments (scape and pedicel) combined, and that there are erect hairs on the front part of the side of the thorax (anepisterum), would definitely be diagnostic for this species if we were in the east. However I can’t find information on the species of the west, let alone their morphology, or a key to separate them.
Chrysotoxum flavifrons is also common in our region, they apparently favor spruce forests like the one in which this one was found, and they feed on the flowers of Cornus sp., which were abundant in that area in the form of Cornus unalaschkensis, so that’s the label I’m sticking on it. If any of you have a better idea, please let me know. And, though I doubt that this is diagnostic it was interesting to me, I found this fly at a UV light at least 2 hours after dark.
Description-Medium sized (11.2-16.5mm) wasp mimic Syrphid fly with yellow face, legs, abdominal lines, two yellow spots on the sides of the thorax, black scutum with 2 pale grey longitudinal lines, and a bronzy green scutellum; flagella of antenna longer than scape and pedicel combined; erect pile on the anterior anepisterum.
Similar species-I cannot ascertain even what all species we have in the west, let alone what might be similar.
Habitat– Coniferous forests up to subalpine; known to frequent hilltops to find mates.
Range-Northern North America; probably region wide in appropriate habitat.
Eats-Larva are possibly associates of root aphids and ants, probably preying on the ant larvae and aphids, and scavenging honeydew; adults are known to visit the flowers of Cornus sp. (dogwoods) and Linnaea sp. (twinflowers), and probably many others.
Eaten by-Larvae are probably parasitized by some Encyrtid wasps; larvae and adults eaten by any insevtivore which can catch them, though the wasp mimicry probably protects many adults.
Reproduction-Nothing seems to be known for sure about the reproductive habits of anything in this genus, though female Chrysotoxum spp. have been observed ovipositing near ant nests.
Adults active-Late May to mid September
Etymology of names–Chrysotoxum is from the Greek words for ‘gold bow/cradle/curved support. I can’t seem to find out to which golden element in the morphology of Chrysotoxum this refers. The specific epithet flavifrons is from the Latin words for ‘yellow forehead’, although the face of this species isn’t any more yellow than several other Chrysotoxum.