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A winged alien could soon devastate commercial geranium crops in the south
of Spain. The alien is a small, dark brown butterfly from South Africa which
in the past two years has colonised all the Balearic Islands in the western
Mediterranean. The first eggs have now been found on the Spanish mainland.

Botanists who have tracked the rapid spread of the geranium bronze (Cacyreus
marshalli) across the islands of Majorca, Minorca and Ibiza warn that it
will cause havoc if it gains a foothold on the mainland. ‘They feed on
leaves and flowers and larvae burrow into the stems of geraniums,’ says
Martin Honey, an entomologist at the Natural History Museum in London.
Spain’s geranium industry is worth £16 million a year.

Already, the butterflies have dismayed gardeners in the Balearic Islands.
‘Ninety per cent of the geraniums are affected,’ says Honey. ‘The population
of this thing has just exploded, and it’s probably the commonest butterfly
you see.’

According to Honey, the butterfly arrived in the Balearics on geraniums
imported from South Africa. Larvae of the geranium bronze have been
identified on imports to countries as far north as Belgium and Britain, but
the butterflies do not survive the colder climates.

‘The Balearic Islands are hot and sunny with lots of scrub, very similar to
the natural habitat of the butterflies in Africa,’ says Gary Roberts of the
Butterfly Conservation Trust. But the butterfly has no natural predators in
the Balearics. Honey says botanists may end up importing predators, such as
wasps, from Africa. ‘But these often cause problems because they may attack
other native species of butterfly,’ he says.

Victor Sarto i Monteys, a Spanish botanist who works for the Service of
Plant Protection in Barcelona, says he has found eight of the butterfly’s
eggs in Alicante – the first on the mainland. A larger number of adults,
perhaps 30, would be needed for the insect to establish a foothold, he says.
Monteys says he is convinced the butterfly will jump to the continent. ‘We
will know only when it is too late,’ he says.