Brexit will not stop all European migrants; in particular, diamondback moths. Biologists have warned of a “biblical” plague of the cauliflower-devouring pests this year, carried to our shores by favourable winds.
Some insects, such as the Monarch butterfly, have a two-way, or homeostatic, migration pattern, returning each year to breeding grounds. Others, such as the diamondback moth, have a one-way “dynamic” migration, always in the same direction. This allows them to re-occupy areas where winters are too harsh to survive. The UK has a small native diamondback moth population, which is occasionally boosted by millions of migrants when conditions are right.
Migrating insects cannot fly against the wind. Some, like winged ants, wait for still air before taking off. Researchers with radar have discovered how weak fliers such as the diamondback moth can migrate for long distances by taking advantage of wind shear, the difference in wind speed and direction at different heights.
The moths rise vertically until they encounter a wind blowing in the right direction. Rather than progressing under their own power, they ride the breeze and are carried along like aerial plankton. When they reach a suitable place, rich in the right sort of greenery, the moths descend.
Moths can ride the winds this way for enormous distances. In 1960, a large migration of diamondbacks was tracked over 2000km from the Baltics. Other insects travel even further. In 1988, swarms of locusts were tracked flying 5000km from Africa to the Caribbean.
