Rather tatty Small White butterfly. They can be seen from March to July. The caterpillar is bluish green with a row of yellow spots down each side and a yellow line along its back. However, if they pupate on fences or walls they are greyish/brown to blend in with their surroundings, clever huh? They feed on members of the brassica family, cabbages in particular and also on garden mignonette (Reseda) and nasturtium (Trapaeolum), which is what has attracted it to my garden.