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For Insects, Spiders & Their Kin
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Photo#18330
Larvae on Potentilla simplex - Periclista

Larvae on Potentilla simplex - Periclista
East Lansing, Ingham County, Michigan, USA
May 24, 2005
Size: 5/8"
Several dozen larvae feeding on Potentilla simplex and Fragaria x ananasa.

Moved
Moved from Sawflies.

green spiny larvae
I found this larva identified as raspberry sawfly (Monophadnoides geniculatus) on a Manitoba Ag website. www.gov.mb.ca/agriculture/crops/insects
We also found the same larvae feeding on raspberry leaves in another location.

 
Convenient followup :)
I was just this second looking at one of these I brought home yesterday thinking it would be a butterfly caterpillar of some sort. Then your comment notification came along and there's the same critter! I just looked at it through a 10x loupe and sure enough, there's too many prolegs for a lepidopteran so it must be a sawfly.

Keep an eye on them
Most larval guides are based on the final instar which often appears different than earlier stages. I'll bet these will grow and become more recognizable.