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Genus Pollenia - Cluster flies

Shady Couple - Pollenia - male Porky II, a clus*ter fly? (Or have I erred again? Joe? Tony?) - Pollenia golden - Pollenia Calliphoridae?  - Pollenia Cluster Fly - Pollenia griseotomentosa - male Cluster Fly - Pollenia Fly - Pollenia - male Fly - Pollenia
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Diptera (Flies)
No Taxon (Calyptratae)
Superfamily Oestroidea
Family Calliphoridae (Blow Flies)
Genus Pollenia (Cluster flies)
Explanation of Names
Pollenia Robineau-Desvoidy 1830
6 spp. in our area(1), hundreds total. It is possible that all six species are introduced from Europe.
Adult cluster flies resemble house flies, but are slightly larger, about 5/16 inch long, narrower and nonmetallic gray. When at rest, they overlap their wings at the tips, whereas the house fly does not. Also, the thorax is without distinct stripes, contains many short, yellow-golden hairs, and the dark gray abdomen is hairy with light and dark patches of color. When crushed, the cluster fly has an odor resembling "buckwheat honey."
Species identification is usually impossible from images alone and may require seeing
thorax from behind (one species has a pattern only visible from behind)
underside of the wing, near the base, to see if a tuft of small hairs is present (a 1:1 or closer macro may be necessary)
posterior thoracic spiracle (to see color)
closeup of mid femur and tibia (to see small hairs)

Key to NA species in (2)
primarily holarctic
Internet References
Biological Survey. Cluster Flies (Calliphoridae: Polleniinae: Pollenia) of North America
Works Cited
1.Keys to the genera and species of blow flies (Diptera: Calliphoridae) of America north of Mexico
Whitworth T.L. 2006. Proc. Ent. Soc. Wash. 108: 689–725.
2.Cluster flies (Calliphoridae: Polleniinae: Pollenia) of North America
Adam Jewiss-Gaines, Stephen A. Marshall, and Terry L. Whitworth. 2012. Canadian Journal of Arthropod Identification.