Lump-legged Swamp Fly

Anasimyia chrysostoma

"Anasimyia chrysostoma" is a fairly common species of syrphid fly observed across the United States and Canada. Hoverflies can remain nearly motionless in flight. The adults are also known as flower flies for they are commonly found on flowers from which they get both enegy-giving nectar and protein rich pollen.
lump-legged swamp fly I believe the two look-alike species are not present on the west coast - but I may be incorrect about this.. A. distincta and A. grisescens are difficult to distinguish from A. chrysostoma  where they overlap. Anasimyia chrysostoma,Geotagged,Summer,United States

Reproduction

Larvae of this genus are of the rat-tailed type living in aquatic environments.

References:

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Taxonomy
KingdomAnimalia
DivisionArthropoda
ClassInsecta
OrderDiptera
FamilySyrphidae
GenusAnasimyia
SpeciesA. chrysostoma