A swift moth (Hepialidae) caterpillar burrows underground eating grass roots. The caterpillar is probably larva of the Common Swift (Korscheltellus lupulina) or the Ghost Moth (Hepialus humuli).
From Wikipedia (http://en.wikipedia.org/wiki/Hepialidae):
The Hepialidae is a family of insects in the lepidopteran order. Moths of this family are often referred to as swift moths or ghost moths. Hepialidae constitute by far the most diverse group of the infraorder Exoporia. There are 60 genera and at least 587 currently recognised species of these primitive moths recorded worldwide.
The maggot-like larvae feed in a variety of ways. Probably all Exoporia have concealed larvae, making silken tunnels in all manner of substrates. Some species feed on leaf litter, fungi, mosses, decaying vegetation, ferns, gymnosperms and a wide span of monocot and dicot plants. Most feed underground on fine roots, at least in early instars and some then feed internally in tunnels in the stem or trunk of their hostplants.
-0.35 exposure compensation in ACR
9 recovery in ACR