It’s halloween, here come the ladybirds!

On warm October days all across the northern hemisphere you may see squadrons of ladybirds seemingly appearing out of nowhere and making a beeline for quiet corners of your house. These are Asian Harlequin Ladybirds, so named because of the huge number of colour forms they occur in (in the US these little beetles have often been nicknamed the Halloween Ladybug, because of the swarms they form in the autumn).

Most of us probably wouldn’t recognise a Harlequin Ladybird, but at this time of year they come into our houses to hibernate, sometimes in huge numbers. While adults of some ladybirds hibernate individually, finding cracks in bark or rocks in which to over-winter, Harlequins hibernate in big clusters, historically in eg caves or hollow trees. To a Harlequin Ladybird, our houses don’t look much different to a cave of course: safe, dry, and usually warmer than outside!

But Harlequins Ladybirds aren’t native to the UK (or the US).

Native to eastern Asia from central Siberia to the Pacific coast, Harlequins are voracious predators of small insects, and were identified as a potential biocontrol agent for aphids and scale insects. Consequently, they were introduced into greenhouses, crop fields, and gardens in many countries, including the United States and parts of Europe. Naturally enough, a winged migratory insect didn’t stay where it was released, and the Harlequin has now reached most of the planet and is regularly described as ‘one of the most invasive insects on earth’.

Released in mainland Europe as a ‘natural pest controller’ Harlequins spread quickly, and were first discovered in southern Britain in summer 2004. Successful, hardy, and larger than our native ladybirds the Harlequin was soon found throughout nearly all of England. The insect conservation charity Buglife noted that it took the Grey Squirrel a century to spread throughout the country – it took the Harlequin Ladybird less than 5 years.

Does that matter?

Harlequins are pretty little insects, but they have big appetites. Larger than our native ladybirds they easily out-compete smaller species, and unlike many ladybirds the Harlequin doesn’t just feed on one type of food. They are now known to feed on other ladybird eggs and larvae (and even the eggs and caterpillars of moths and butterflies) as well as aphids.

Given that they may impact populations of native ladybirds and don’t ‘belong here’, should we be reaching for the insect spray?

While Harlequins may have an impact on some native species, they are now so well-established that it is effectively here to stay whether a few of us remove them or not. And nature has a way of redressing the balances we upset anyway: existing native predators, such as a parasitic wasp that lays eggs on ladybirds, have started preying on Harlequins. Eventually numbers are expected to reach some form of equilibrium.

Besides Harlequins are nothing for us to worry about. They don’t damage furnishings or clothes (they do produce a rather smelly yellow fluid if they’re ‘attacked’ though), they can’t give us any diseases (a ridiculous scare-story once spread about ladybirds transmitting venereal disease to humans which is unequivocally untrue), they can’t hurt us, and they’re not realistically going to exterminate any of our native wildlife.

If they really bother us, perhaps we should just make sure that our doors and windows are fully sealed and insulated?

Could we learn from them instead?

Harlequin Ladybirds are actually fascinating little things. Maybe we should learn about them and teach our kids about them instead. Why do they – and other animals – hibernate in large groups, for instance? How do they leave behind ‘invisible’ scent trails that linger from year to year (which can be removed with strong detergents, but which is worse – a chemical cocktail with possible negative environmental consequences or a pheromone which we can neither see nor smell?). They are a very real warning about what happens when we move animals and plants around the world without proper consideration – why don’t we teach the dangers of doing that? Besides all else, they’re a good example of how wildlife adapts to changes in the environment.

Our answer to wildlife so often involves demonising and/or destroying it. Ladybirds of all species have as much right to survive as we do. And like with many species before it, any ‘problems’ are our fault: we moved Harlequins around the world. And spraying them? Insecticides are incredibly powerful toxins that can’t target specific species and often linger in the environment destroying insects of all kinds: native ladybirds like seven-spots sometimes hibernate with Harlequins as well, and no pesticide can tell the difference between a ‘good’ insect and a ‘bad’ one.

Time will tell what damage the Harlequin will cause, but there are so many instances of accidental or deliberate introductions causing ecological damage now that we’d surely be extremely careful not to facilitate another one? Unfortunately, as anyone watching their local Ash trees for signs of Chalara fraxinea (the fungus that causes Ash dieback) will know, that is sadly not the case…


To hear from an expert on the problems of insecticides and our attitude to insects have a listen to this War On Wildlife (WoW) Short with author and academic Adam Hart, Professor of Science Communication at the University of Gloucestershire. Adam suggests we should cherish ‘the small things’. [Duration 0:01:12]