Something seems to be nibbling the flowers on my broad beans.

There are small holes at the base of the flower, on virtually all the flowers. The only flowers which aren't affected are the very newest, and soon these too will also be attacked.

The only insects I've seen near the plants are bees, but they are also covered in ants. I've not seen them attacking the flowers - they just seem to feed at some browny black spots on leaves.

I get the feeling that these attacks may be killing the beans, as I can't see any pods forming.

Any ideas?