My trip to the South West back in June was extremely rewarding. One of the many highlights was seeing a Large blue butterfly at the National Trust’s Collard Hill in Somerset.
The Large blue butterfly is one of the rarest butterflies in the UK and actually became extinct as a native butterfly in 1979, but since then it has been successfully re-introduced. However, Collard Hill is currently the only place in the UK where the public have access to see this butterfly during the few weeks in summer when it is flying.
Despite it’s name, it’s not particularly big! Though it is the largest of our blue butterflies, its size can vary and is relatively small in comparison to many of our other native butterflies.
Our first sighting was of one nestled in some grass close to the footpath…
Their markings are also variable – but the deep blue upper wings fringed with black and unmistakable arch of black spots on the forewing (in most cases looking almost like a paw print) are diagnostic…
The reason for the Large blue’s rarity is due to its curious lifestyle which involves spending the majority of its life-cycle as a larvae and pupae within the nests of red ants, where the larvae feed on ant grubs!
Its life-cycle was not fully understood until the work of Jeremy Thomas in the late 1970’s and the key discovery of its dependence on a particular species of red ant (Myrmica sabuleti) which itself requires specific environmental conditions in order to survive (i.e. warm, well drained grassland with a very short sward and the presence of wild thyme). Unfortunately, this discovery came too late to save it from extinction and it was the absence of this particular red ant from many of the former sites which ultimately led to the loss of the Large blue in the UK.
It was a privelege to see this once absent species which is now, thankfully, a success story – bouncing back in a number of locations across the South of England.