Further to Pammi's question of 23 May
By Jomed
United Kingdom 
Little green caterpillars have totally devoured leaves on my neighbour's ash tree. All that remains are the skeletons. I wonder whether anyone can shed any light on what the caterpillars/pests might be as I am unable to find anything on the internet, despite hours of searching.
15 Jun, 2009
Answers
Many thanks for your response. I had done some research on the sawfly and did think that was what it could be. There are nesting boxes and bird tables and there are a large number of blue tits who visit so, fingers crossed, they'll manage to devour the huge population .......although it may take some time! I was thinking that maybe there's a sawfly infestation as this has never happened before!
16 Jun, 2009
Yes, they do go in waves like any infestation...remember all the ladybirds a few years ago? You'll just have to wait and see if they recurr.
17 Jun, 2009
They are probably some kind of sawfly. These are not completely specific to a particular plant ( I had gooseberry sawfly on a willow) so may not be listed under 'ash sawfly', but sometimes they mention the other plants they attack on the websites. The leaves should grow back as it's early summer. Unfortunately the caterpillars drop off and pupate, then fly back up and lay more eggs, sometimes 3 per summer!! Encourage blue tits etc to your ash tree with food.They will then eat the caterpillars (hopefully!). Spraying is probably out of the question.
15 Jun, 2009