Insect Identification Restores Large Blue to UK
One Red Ant Species Needed for Butterfly Success
Jun 17, 2009
The Large Blue Butterfly (Maculinea arion) became extinct in the UK in 1979, but detailed studies between 1972 and 1977 provided the information necessary for successful re-introduction and conservation.
Life Cycle of the Large Blue Butterfly
The butterfly lays eggs on wild thyme, and the caterpillars that hatch out fool red ants into taking them back into their nest. These caterpillars spend the winter protected by the ants, and in return the ungrateful wretches kill and eat young ants! Insect identification (of the ants), and a study of the precise requirements of these ants, revealed the cause of the extinction and suggested management strategies for conservation once the Large Blue was re-introduced.
This is how it goes:
- The caterpillars depend on one species of red ant (Myrmica sabuleti) for survival over winter.
- The ant needs exactly the right soil temperature to survive.
- The precise length of the grass influences soil temperature – 1 cm of grass can cause a 2-3 degree change!
- Changes in animal husbandry, and reduction of rabbit populations by myxomatosis, allowed grass to become longer, cooling soil and killing the ants.
- Swedish butterflies were released in suitable habitat in 1983.
- Grass was cut to the required length and maintained by re-stocking with the appropriate number of sheep.
- The ants returned.
- The Large Blue is thriving once more.
Jeremy Thomas (of the University of Oxford UK) studied the breeding success of the last small colonies of UK Large Blues, counting eggs and observing the behaviour of the caterpillars.
- The adults lay eggs on the flowers of wild thyme, and the young caterpillars have a ‘honey gland’ on their rear end.
- Red ants drum on the ‘honey gland’, and the caterpillar wiggles like an ant larva.
- The ant collects the sweet secretion, which smells like young ants, and carries the caterpillar into the underground nest.
While many species of red ant behave in this way, only Myrmica sabuleti is completely fooled – keeping and guarding the caterpillars through the winter. The caterpillars eat ant larvae until they pupate and emerge as adult butterflies in the following spring.
Conservation Benefits
The Large Blue is a ‘flagship’ species (rather like the Giant Panda or Mountain Gorilla), and in order to conserve it the habitat must be restored and maintained. When this is done many other species benefit, and Thomas has said “ … there have already been dramatic increases in rare birds, plants and other butterflies, such as the wood lark, pale heath violet and the pearl-bordered fritillary …”
Presumably the ant will also do well, and maybe the spider (Zodarion rubidium) – which mimics Myrmica sabuleti and eats them – will also benefit. This spider was once restricted to southern France, but with global warming it is moving north (much like the Rosemary Beetle).
Understanding the requirements of any species needs detailed study, in this case involving precise insect identification.
Reference: Kathy Wren, ‘Science: Researchers Publish the Discoveries that saved the Large Blue Butterfly’, Journal of American Association for the Advancement of Science, online, June 15, 2009.
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