The Rat-Tailed maggot - Eristalis tenax - is the larvae of the Drone Fly, or Hover Fly. It lives in standing water.
Rat-Tailed Maggot

Nathan Reading [CC BY-NC-ND 2.0], via Flickr
The Rat-Tailed maggot - Eristalis tenax - is the larvae of the Drone Fly, or Hover Fly. It lives in standing water.