Massive Rove Beetle

[Zephyr]

I found these in the compost bin of a local community gardening project. They are massive. I may have seen an adult 2 years ago and if I recall correctly they are just as impressive. I hope to collect more (I have 2 still alive, 2 others died possibly due to collection-related injuries ): )

If they're like other rove beetles breeding them should be easy! Any ideas on an ID?

 

[What]

Probably Tasgius sp. ? I believe those are the typical large roves of the eastern US.

[Peter Clausen]

It's hard to see the vestigial elytra in that photo, but I'd have guessed it was a ground beetle larva from the pale coloration of the abdomen and cerci (and size). Did you confirm whether or not they have flying wings under the elytra? I'm always surprised to see rove beetle flying, though I don't know what proportion of them do so.

[Zephyr]

I'm pretty sure this specimen is immature. I've seen Tasgius species around here and these monster dwarf them. I figured they could be hairy rove beetle larvae but these are even larger than those.