[mdjlucan]

I've got a box Bush and it is full of these creatures what are they

[mumofstig]

They look like Box Tree Caterpillars shown on the RHS site

https://www.rhs.org.uk/advice/profile?PID=760

[londongardener]

I really don't like saying this - but with box moth caterpillars you have to squash them - or feed them to the birds.  Normally I don't squash things apart from Gooseberry sawfly.