Ants?

Jon Topping

No, it's not ants, but lily beetles. Look out for bright scarlet beetles and squash them. Their young look a bit like bird droppings as they cover themselves in their own excrement - have a good look for these and wipe them off.

Lokelani

Yes if they lay eggs the young look like horrible brown blobs underneath the leaves. 

Pick them off carefully, if you drop them they tend to land red side down & it's much harder to spot their dark undersides on the soil. 

Jon Topping

Brilliant thank you, I've just had a quick look but not found anything yet, do they hide for the evening.

nickybs

In my experience,which is, unfortunately, annual, they seem to start off on the lower leaves and have a nasty habit of letting go the minute you touch the plant so, as Lokelani says, they can be hard to spot. Best to wait until tomorrow and you'll find them easier in the daylight. Take lots of kitchen roll with you to put the young in as they are really gross and slimy! Happy squashing