If it weren’t for the weather this would be a great time to go butterfly hunting, with many British species on the wing taking advantage of the many flowering plants and the sun’s warmth. One group of butterflies, the Blues, are a tricky bunch to identify and seem to rarely settle or allow close observation but are amongst our most pretty species of Lepidoptera. This week I bring you facts about the most familiar blue species – the Common Blue Polyommatus icarus

This is a widespread insect that I have encountered in a variety of habitats from gardens to downlands, usually only getting a fleeting view as one speeds past, however the other day I came across one that due to the weather was more obliging. I was walking up on the South Downs in low cloud when I noticed out of the corner of my eye the shape of a butterfly with wings spread sitting atop a blade of grass. I crept closer with camera ready, noting that it had orange spots on the hindwings and a blue sheen that did not quite cover the wings, fading to brown at the edges. It must have seen me for it sped off before I could get close enough for a picture, however I followed it with my eyes and watched as it landed a short way off at the edge of the path. It wasn’t good flying weather for butterflies and this time it had landed down among the grass stems with wings closed. I managed a few pictures of its patterned underwings which enabled me to later identify it as a Common Blue female.

  • It is not so reliant on ants as some other Blue species but the caterpillars and chrysalis’ both produce honeydew which attracts ants – which will protect them or even carry them back to their nests.
  • Common Blues have two main broods, one in May-June and another August-September though in a good year in the south of England they can have a third brood in October.
  • The larval food-plants consist mainly of Fabaceae species such as Bird’s-foot Trefoil and Restharrow as well as Black Medick, White Clover and other trefoils. The butterfly can occur anywhere these plants are found right across Britain.
  • Males can be told apart from Adonis Blues from the different shade of blue on their wings and the lack of dark lines along the white margins of the wings. Females are often mostly dark brown with some dark blue near the body but can also show much more blue on the wings, particularly in the north.
  • It lives in discrete colonies, though is capable of rapid colonisation across distances, this makes it a good indicator of habitat health as any change in an areas suitability or foodchain will rapidly affect colonies.
  • They have recently been found as an alien introduction in Canada, where they are spreading rapidly.