Whats eating the cabbage??

Right i know ive been getting pests in my polytunnel and its only last couple of days its been a real issue. i can see mice have been at my peas ive just sown, and slugs at my lettuce but im at a loss as to what has been at my new cabbage seedlings? They are up high on my staging but it almost looks as if they have just had the top parts snipped off and just the stalks left!! Very straight cut like if you had used a pair if scissors  and only a couple of them, the rest so far have been ok. Does anyone have a clue??