The large blue butterfly, Phengaris arion has been a protected species in England for almost a century. In spite of protected areas set aside for the butterfly, numbers dwindled and went extinct in England in 1979. At the time, the extinction was attributed to collectors.
Subsequent research found the caterpillars to be predators on Myrmica sabuleti, a species of ant. The caterpillars are able to trick the ants into carrying them into their nest where they feed on ant eggs and larvae. Myrmica sabuleti thrives on recently burned grasslands and are rare in areas of mature vegetation. Original efforts to protect the butterfly excluded grazers, fire, and mowing to promote the growth of wild thyme, the host plant of young larvae. However, these efforts inadvertently made em>Myrmica sabuleti rare within the preserve and promoted decline of the butterflies.
More recently, populations of the large blue have been reintroduced into England under conditions that promote em>Myrmica sabuleti. Those populations are thriving under the new habitat management.