Monday, 19 October 2009

Harlequin Ladybirds by Polly McEldowney

The word 'Harlequin' sounds innocuous enough, conjuring up images of a diamond-clad theatrical clown. But the Wikipedia entry reveals the character may have been originally based on a more sinister figure from medieval French passion plays. 'Hellequin, a black-faced emissary of the devil, is said to have roamed the countryside with a group of demons chasing the damned souls of evil people to Hell. The physical appearance of Hellequin offers an explanation for the traditional colours of Harlequin's mask (red and black).'

A slightly less frightening new visitor to Chorlton is the Harlequin ladybird, but it is not without negative connotations of its own. Harmonia axyridis is a new species to the UK, having arrived in the South of England in 2004 and rapidly spread across the country. I have seen it in Manchester for the first time this autumn, and it is quite possible you have too, as it has made a rather dramatic entrance. It is much bigger than most of the other 25 species of ladybird native to the UK, and is rarely seen alone, sometimes aggregating in groups of thousands or even tens of thousands. There have been scenes around Chorlton recently that are reminiscent of the summer of 1976, when unusually hot weather led to an explosion in the population of the 7 spot ladybird, Adalia 7-punctata. A brief stroll round my back garden has just revealed a cluster of 30 on a green surface. The harlequin ladybird's success arises partly from having a longer breeding season than other ladybirds, such as the 7 spot which has only one generation a year. But the harlequin will continue to breed as long as it is warm enough and there is food available, having two or more generations a year. I've spotted harlequin larvae in my garden this week, and it's nearly the end of October. Most other ladybirds will have sought out places to hibernate by now. Another huge advantage is that it is more of a generalist feeder than other ladybirds, which tend to stick to aphids as a food source. The harlequin is a highly effective aphid predator but can also broaden its diet when aphids are scarce, eating the eggs and larvae of other species, including butterflies and other ladybirds. It will even suck the juice from soft fruit.

So, outcompeted and outnumbered, our hitherto common species of native ladybird could be in big trouble. Is there anything we can do? The best thing for now is probably just to monitor sightings on the UK harlequin ladybird survey website. Identification isn't straightforward as there are over 100 colour patterns of the harlequin ladybird. They can have black spots on a red background, or red spots on a black background. The main giveaways are the size (6- 8mm) and the fact that they're wandering round in October. Another common characteristic is an M-shaped mark on the pronotum (the back of the head). Be careful when getting close to them though; they have a defence mechanism where they exude a toxic chemical, 'reflex blood', which can be quite painful to humans. This creature is best admired from a distance!

Polly McEldowney, October 2009

I learned that Polly had an interest in this subject last week and asked her if she would consider contributing an article to the blog. She tells me that she "finally cracked" when she found a Harlequin Ladybird in her hairbrush! - Ed.

1 comment:

Anonymous said...

I meant to mention these when I was round, we've had hundreds of them. Amazing little creatures, seemed to the love the newly glossed window sills, which I rescued them from....and are now complete with ladybird foot prints. fantastic.