Big blue butterflies have been breeding at the highest level for 150 years

The great blue butterfly was reintroduced to the UK in 1983 and flew in its largest number since registration began in the largest number of locations in 2022.

Thanks to meticulous conservation efforts by a collaboration of scientists and conservation agencies, South West England now supports the largest concentration of great blues known in the world.

The big blue has a bizarre life cycle.

After feeding on the wild thyme or marjoram flowers for three weeks, the caterpillar produces odors and songs that lead red ants to believe it is one of their own larvae, and is carried underground into the ant’s nest and placed with the brood. The caterpillar spends the next 10 months with ant larvae before pupating in the nest the following year and then crawling above the ground as a butterfly.

Despite more than 50 years of efforts to halt its decline, the great blue was declared extinct in Britain in 1979.

Its reintroduction in 1983 was based on the discovery that large blue caterpillars can only survive in the nest of a particular species of red ant, Myrmica sabuleti. Landscape management changes were responsible for the extinction. Changes in grazing made the remaining wildflower meadows too high and too shady for the heat-loving red ant. These trends have now been reversed through targeted grazing – tailored to optimize turf structure in each interconnected site – so far in two UK landscapes.

As knowledge grew, it was possible to create a new large blue habitat from scratch on arable land, failed plantations and new railway constructions – the ultimate test of what is already the largest and longest-running successful conservation program for any endangered insect in the world. .

A total of 12 new sites are being restored to flowery meadows suitable for big blue breeding, either ‘starting from scratch’ on arable land, failed conifer plantations and railway construction, or by restoring custom grazing to degraded lower lands. These already support up to a third of the UK population of great blues, up from just 7% in 2019.

These restorations of a disappearing type of wild pastureland have also provided ideal breeding grounds for many other rarities that share the habitat of the great blue parts. Among plants, the extremely rare pasqueflower and cut-leaf self-healing have reappeared and/or spread under ‘great blue management’, along with up to 12 species of orchids.

A remarkable number of insects have increased on, or newly colonized, the 12 restorations. Nationally endangered species include the shrill maple bee (the UK’s second most endangered bumblebee), the rock rose pot beetle (known from just five UK sites), the downland villa beefly (not registered in the UK for 50 years) before 2000), and the strange shaggy oil beetle (only found at about 30 UK sites). Eight butterflies that are on the Red Date List—Duke of Burgundy, Little Blue, Adonis Blue, Brown Hair Stripe, White Letter Hair Stripe, Little Heather, Gray Skipper, Dingy Skipper — also bloom alongside abundant displays of more common or local insects and plants.

These restorations represent the largest and most innovative next phase of Great Blue restoration in Britain. Aside from the benefits of other rare species, they are important internationally as the great blue species is listed as one of Europe’s most ‘endangered’ insect species, and worldwide as well.

The 12 sites link or expand more established populations, spanning two landscapes in the middle of Somerset and, more recently, in the Cotswold Hills of Gloucestershire, which is now home to a promising foothold.

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