I happened to look down and saw this very small caterpillar being tended by ants. It was feeding on Bird's foot trefoil (Lotus corniculatus), a member of the Legume family, and a favourite of silvery blue larvae. This is what the adult looks like: http://www.pbase.com/laroseforest/image/124513471

Just realized I should add something about what is going on with the ants. They are protecting the caterpillar from predators, in return for which they get to feed on a sweet 'honeydew' that the caterpillar exudes. An example of a symbiotic relationship at play.