What is eating my plants?

Last weekend I planted out in a freshly dug over bed that previously had strawberries in, some different varieties of kale and spring cabbages.  I used hoops and debris netting to keep out the birds and anything landing on the plants to eat it. 
The netting was secured down and I checked, and double checked to make sure nothing was going to get through or under my netting.  The netting is brand new so it does not have any holes in.  I put down some slug pellets in hope to stop the slugs from eating them as they have done before. 
I returned yesterday to find I have just stalks, well in some cases not even stalks, but no slime from any slugs, no birds or bugs anywhere to be seen.   The only other thing I do see around my plot is tiny little spiders about the size of a 5 pence coin, they are everywhere but never seen them on any plants of any kind over the years I have seen these spiders, so I don't think it's them.  I am at a loss to what it could be, does anyone have any ideas?

I will be interested in any replies on this as mine are the same... Kale, tucked up inside netting, pellets down, checked for caterpillars, eaten away leaving the centre stalks.  It did look to be worse near the netting so the only thing I can think of is snails.

Overnight my carrot green have been stripped  on closer inspection a big fat hungry caterpilar looked very smug indeed.

Hes gone to devon on a very long holiday.