Tuesday, 3 February 2009

Alien Invaders

Today I saw the first Harlequin ladybirds of the year. Two individuals adjusting their position in a railing to catch the winter sun. In September 2006, I came across a beautiful, but strange, ladybird. Yellow, large and with 21 spots, I had never seen anything like it, and it wasn't in the insect guide I checked at home. A few weeks later, I found a large black ladybird with black spots. I had a little plastic container with me and took the insect home to photograph it. This time I took a bit more time to identify it. It was a Harlequin, a non-native ladybird species that since 2004 it has rapidly spread across the UK. The Harlequin is native from Asia, and has been widely used as pest control in greenhouses, from where it has escaped. The species had spread invasively in the USA and mainland Europe, from where it invaded the UK.
 This ladybird is unique in that it shows a large variation in color patterns between individuals. The following photos, all taken in Hull, illustrate this.
There was already a very well organized survey to follow the spread of this species in the UK, the Harlequin Ladybird Survey, and I reported these sightings. Data sent by members of the public (in the form of records and photographs) have helped to follow this invasion in great detail. This series of maps from the survey's website show the spread of the Harlequin in the UK year on year.
There is lots of info from the website, not only on the Harlequin, but also on the native ladybirds. You should be able to identify not only the adult ladybird, but also the larva. Here you can compare it with a 7-spot larvae.
Harlequin ladybird larva (with two lines of reddish spiky tufts on top of abdomen).
A 7-spot ladybird larvae (only black tufts on top of abdomen). Tufts are not obviously spiky.
Should we be concerned? Despite the Harlequin being a quite handsome bug, there are fears its explosive spread could result in threats for other ladybird species, either directly or indirectly. They are reportedly very aggressive toward other ladybirds and even humans! Although I must say I have often collected them by hand and they seem not to be aggressive when being handled carefully, in the same way the 7-spot. They eat larvae and eggs of ladybirds if aphids become scarce. Their populations might not be kept in check by predators and parasites. Also, they hibernate in houses in a communal way and they can become a nuisance.
 In Hull, the Harlequin became very common in 2007, but didn't see many in summer 2008, maybe the gloomy, wet summer didn't suit them!

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