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Brown Argus, Aricia agestis butterfly, roosting on grass
Brown Argus (Aricia agestis) butterfly roosting on grass. Photograph: Bob Gibbons/Alamy
Brown Argus (Aricia agestis) butterfly roosting on grass. Photograph: Bob Gibbons/Alamy

British butterfly defies doom prediction to thrive in changing climate

This article is more than 11 years old
Brown Argus, once rare and declining, depended on one plant species but warmer temperatures have helped it expand range

A modest but resilient British butterfly has bucked the trend of worried predictions about the species' health, with scientists reporting it appears to have benefited rather than lost out from climate change.

The Brown Argus, Aricia agestis, named after a 100-eyed giant in Greek mythology because of the multiple eye-like dots on its underwing, has long been dependent in the UK on a single plant species, the rockrose Helianthemum nummularium. It appears this is probably because the plant tends to grow on south-facing slopes and absorbs the warmth and sun which the butterfly's caterpillars need.

But hundreds of records kept by amateur butterfly enthusiasts since 1990 show that Brown Arguses have expanded their range by 40 miles in the past two decades, moving north at more than 2.3 times the average pace of other flourishing insect species.

Research published on Thursday in the journal Science by five experts led by Rachel Pateman of York university shows that the butterfly is now within a few miles of her labs on the Heslington campus. Its startling advance is credited to warmer temperatures encouraging the caterpillars to try other foodplants, notably geranium species, especially dove's-foot cranesbill.

The group, which includes members from the Natural Environment Research Council's base in Oxfordshire and Butterfly Conservation in Dorset, says that the butterflies appear to have adapted very quickly to new foodplants, for egg-laying as well as caterpillar diet. On the continent, where the Brown Argus ranges from the Pyrenees to Iran, geranium species are commonly used, and a closely-related butterfly, not yet found in the UK, is called the Geranium Argus.

"Ecological and evolutionary adjustments by the butterfly, interacting with alternative host plants that differ in their niches and life-history traits, have resulted in rapid range expansion of this previously rare and declining butterfly," says the study. "We suggest that altered interactions among species do not necessarily constrain distribution changes but can facilitate expansions."

Research on global warming's effect on the natural world acknowledges that there can be benefits as well as actual and potential disasters, and also recognises the ability of species to adapt. The United States Environmental Protection Agency notes a marked northward movement by invertebrates and insects, which form 97% of all animal species. The Brown Argus phenomenon conforms to the pattern, at the fastest end of the process.

An even more dramatic range-leap by a butterfly – albeit involving a hitch on a plane – involves the Geranium Bronze, a little smaller than the Brown Argus but equally tough. It first arrived in Europe in 1987 in ornamental pelargoniums sent from South Africa to Majorca, reached the UK in 1997 and, although seldom seen since, is being monitored as a potential pest to the horticultural trade.

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