T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network

Cranefly nymph (Genus: Mischoderus)

Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Hexapoda
Class: Insecta
Subclass: Pterygota
Order: Diptera
Suborder: Nematocera
Family: Tanyderidae
Genus: Mischoderus

Mischoderus is a primitive cranefly in the family Tanyderidae. 
The larva differs from the tipulid cranefly larvae in that the head is not retracted into the body, and instead of a spiracular disc ((breathing apparatus at the tip of the tail)) there is a cluster of tentacle-like tail filaments (or only 2 slender filaments in early instars). There are no thoracic prolegs, but there are anal prolegs at the end of the abdomen.
Mischoderus larvae are found in many farmlands and bush covered, hard bottom and soft bottom streams, though usually in low abundances.
They are known to have ingested a range of streambed foods including plant detritus, algae and midge larvae. 
Many crane-fly larvae are aquatic and are an important food source for our native fishes and trout.

They are known to feed on
Plant material
Achnanthes lanceolate (algae)
Fragilaria vaucheriae (diatom)
Staurastrum (green algae)
detritus (organic matter produced by the decomposition of organisms)
Polypedilum (non-biting midges larvae) 
This list may not be complete but is based on published studies

Late instar larva with tail filaments

A pupae of a Crane-fly (Tipulidae) ready to hatch into an adult when caught.

Thanks to Wikipedia for text and information: https://creativecommons.org/licenses/by-sa/3.0/