A migration miracle
Species: Painted lady Weight: 0.2-0.3g Range: 5,000+ miles We’re used to strong-fl ying insects migrating to the UK from Europe. But the painted lady butterfl ies we see in warm summers easily beat that. Most specimens start as
d
caterpillars in the Sahel region of Africa. As spring begins they move north over the Sahara, some making it to Southern Europe and the Med, others only getting to North Africa. With summer on the way, the
next generation continues the journey north. Research shows some individuals hop directly from North Africa to the UK. Others fi lter through Central Europe and then into the UK across multiple generations. But here’s the amazing bit: in the autumn, they’ve been found to fl y 5,000+ miles back in a single generation!
Key
Spring migration north Autumn migration south
service of free biological pest control
They do an incredible
Croatia reveals that harlequins are attracted to the lights on ships – they are literally being ferried around Europe.
For all the scares about marauding “invasive” insects – and there is genuine concern about the honeybee-devouring Asian hornet – most migratory insects perform crucial “ecosystem services”. Jason Chapman has studied the Marmalade hoverfl y, our commonest species. To his surprise, these show an ability to choose favourable days for wind-
assisted migration. Hundreds of millions arrive in the spring; up to a billion depart each autumn. “The really exciting numbers,” says Chapman, “are when you calculate how many aphid pests are eaten by the hoverfl ies’ larvae. You rapidly get into the trillions. We think they are doing an incredible service of free biological pest control.”
For all the great insect clouds of old, only now are we gaining a sense of the true scale of insect migration. Migratory ecologists looking at radar data have revealed a startling fact: a biomass of 3,200 tonnes of migrating insects. Imagine 270 London buses made from solid insects passing over southern England each summer. Or, if you prefer, roughly 3.5 trillion insects. That’s an awful lot of bird food. And each one a minuscule everyday miracle.
Top sites for but erfl ies
Our nature reserves are home to dozens of butterfl y species, including (see below) some of the UK’s rarest. But for these insects and other wildlife to thrive, we also need country- wide networks of wild spaces, and you can help. For tips on butterfl y-friendly gardening, visit
wtru.st/butterfl y-garden
Daneway Banks
GLOUCESTERSHIRE WT 37 species. Second largest known population of large blue.
Hutchinson’s Bank
LONDON WT 35 species recorded. This is one of the UK’s best sites for the small blue.
Lydden Temple Ewell KENT WT
34 species
including the Adonis and
chalkhill blues. One of Europe’s fi nest chalk downlands.
Llanymynech Rocks
MONTGOMERYSHIRE WT 33 species, including the very rare pearl-bordered fritillary.
Natural World 39
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ELLEN WINTER
LONDON WT
RAY LEWIS
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