One of the rarest and most fascinating wild species in the UK is expected to make an appearance this summer.

The National Trust said visitors to Collard Hill in Somerset will have the chance to see the Large Blue Butterfly, which has suffered a decline over Europe due to changing farming practices.

The precise time when the butterfly can be seen, depends on the weather, but the main flight period is from mid June to early July each year.

In fact it became extinct in the UK in 1979 and its reintroduction has been a wildlife success story.

The Large Blue begins life as a normal caterpillar and the young larvae feed on wild thyme flowers.

From then on its life depends on an elaborate contrick. As each larvae drops to the ground, it secretes a sticky sugary substance which is irresistible to ants.

The ants are tricked into thinking that the larvae is a lost ant grub and take it into their underground colony.

But not any old ant will do, only large colonies of a single species of red ant Myrnica sabuleti can act as a suitable host. An incredible phase in the caterpillar's life then begins where for ten months it turns into a carnivore - eating the ant grubs while hapless ants feed it and care for it as one of their own.

The sneaky caterpillar then pupates in the ant nest, finally emerging for a few brief days in the last stage of its remarkable life as a beautiful blue butterfly.

These final days, which for a few weeks this summer the public will be able to see at Collard Hill, are a frantic struggle to find a mate and for the females to lay their eggs on the wild thyme in order for the cycle to begin again.

Now the butterfly has been reintroduced to eleven sites across South-west England, four of which are owned by the National Trust, after a major partnership project set up in the 1980s.

The locations have been kept relatively secret to minimise disturbance and help scientific research.