Blow-ins: wind responsible for UK insect invasion

Human actions aren’t always the reason exotic species are introduced into ecosystems, researchers suggest. Sometimes it’s simply a function of bad weather.

A team of scientists led by Pilvi Siljamo from the Finnish Meteorological Institute in Helsinki, Finland, decided to look at the case of the Harlequin ladybird (Harmonia axyridis), a European species that was first noted in the UK in 2004, and became very rapidly established shortly thereafter. {%recommended 7887%}

Given that there was no official plan to introduce the insect – as a vector for biological control, for instance – and that a ladybird seems an unlikely choice for eco-terrorism, the Harlequin’s arrival was generally seen as the result of an accident. Some speculated that the foundation population may have come across on one of the ferry services that ply the English Channel between the UK and Europe. 

Siljamo and colleagues, however, had other ideas. 

The researchers combined the geographic records of Harlequin discoveries in the UK in 2004 and 2005 with weather events in Europe occurring at the same time. They found a strong correlation between new sightings and cross-channel airflows.

The ladybirds, it seems, were being picked up by the wind on one side of the waterway and being dumped on the other.

“We show that the distribution of this species in the early years of its arrival does not provide substantial evidence for a purely anthropogenic introduction and show instead that atmospheric events can better explain this invasion event,” the researchers write in a paper lodged on the biology pre-print repository, biorXiv.

Suitable airflows, they report, are “relatively frequent”, and range from once a week out of Belgium and the Netherlands, to twice a week across France.

“Given the frequency of these events, we demonstrate that atmospheric-assisted dispersal is a viable route for flying species to cross natural barriers,” they conclude.