Help Identify Caterpillars

[Graham Dixon]

I would appreciate it if anyone could identify the "caterpillars" that I am
finding inside rolled up nettle leaves in my garden (Hoghton nr Preston in
Lancashire - UK)

Description:-

Length - 35 - 40mm
Colour - Green with faint dark line along middle of back (When moving, it
is apparent that the green skin is transparent, the dark coloured
'digestive tract" can bee seen)
Prolegs - Segments 6,7,8&9 (4 Pairs)
Head - Green (Black at the front)
Thoracic Plate - Green with black spot on either side
Spiracular line - Very faint but visible. Spiracles do not show up as spots
Anal Claspers - Yes but unable to make out any detail on Anal Plate except
that it is green
Bristles - Very sparse

Fast mover, appears to be quite comfortable moving backwards as well as
forwardsproduces silk.

Thankyou

Graham Dixon