Where did the Harlequins go?

So here’s a little nature mystery that we’re just going to ‘put out there’: why wasn’t our house a home for Harlequin Ladybirds this winter?

Before we even attempt to answer that, many people may not know a Harlequin Ladybird from a ‘normal’ ladybird. Well, they come in a large number of colour forms (and an even larger range of vernacular names), but most of us might recognise them because of an interesting survival trick they have up their tiny sleeves: over-wintering in large groups in our homes.

While adults of many other ladybirds hibernate individually, finding cracks in bark or rocks in which to over-winter, Harlequins spend the off-season packed together in large, motionless clusters. Historically that would have been in caves or hollow trees, but to a Harlequin Ladybird, our houses don’t look much different to any other dark nook of course. Safe and dry, even our leaky sieve of a home here on the Common Ground is usually warmer than outside...

In North America these little beetles are nicknamed the ‘Halloween Ladybug’, because they begin to make their way indoors in the late autumn. That’s when we usually start seeing them too. This year, though? Ones or two crawling around the corners of the windows or up amongst the beams, but not the tight groups of hundreds we’re used to living with through the winter.

Where had they gone? Maybe we should delay answering that question by asking another: how did they get here in the first place? Because while they’re common now, Harlequin Ladybirds aren’t actually native to the UK (or to North America). In fact they were first found in England less than twenty years ago

Originally from eastern Asia (from central Siberia to the Pacific coast), Harlequins are voracious predators of other small insects. In a sadly typical example of ‘Have we thought this thing through properly?”, this now rampant ladybird was identified as a potential biocontrol agent for aphids and scale insects, and was introduced into greenhouses, crop fields, and gardens in many countries - including parts of Europe.

Released in mainland Europe as a ‘natural pest controller’, just as naturally this highly mobile insect didn’t stay put. It began to spread quickly, and was first discovered here in southern Britain in summer 2004. Successful, hardy, and larger than our native ladybirds the Harlequin was soon found throughout nearly all of England, leading the conservation charity Buglife to wryly note that while it took the Grey Squirrel a century to spread throughout the country, it had taken the 10mm Harlequin Ladybird less than five years.

In fact the Harlequin Ladybird has now reached across the planet, and is now regularly described as ‘one of the most invasive insects on earth’.

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. As well as the aphids they were brought over to chomp down on, they are now known to feed on other ladybird eggs and larvae, and even on the eggs and caterpillars of moths and butterflies.

Which on top of all the other man-made problems assailing our declining insect populations is NOT a good thing. So how should we respond? These little ‘bugs’ didn’t ask to be brought here, and while they might feast on native insects, there’s no evidence yet that they’re likely to cause any long-term declines or extinctions. And Harlequins certainly don’t do us any harm. They don’t damage furnishings or clothes, 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 (pest controllers love to talk about how Harlequins bite, but Harlequins are very small and controllers have services they want to sell). They will leave a smear of blood (an unpleasantly smelly yellow fluid) behind if they’re handled roughly, but if they’re left alone they tend to just head back outside once the weather warms up.

Jo and I have always just let them be. We don’t bother them, they don’t bother us. And native ladybirds like 7-spots often over-winter with Harlequins, anyway, so even if we think we are ‘helping our plucky Brit ladybirds fight off the invaders’ by destroying clumps of Harlequins we actually run the risk of killing other ladybird species too.

But what has all of this to do with NOT finding any Harlequins in the house this year, you might reasonably be asking by now? The thing is that the garden was packed with the larvae of Harlequin Ladybirds last year. They’re distinctive once you know what to look for and one of our little nettle patches had literally hundreds crawling over it in the summer. I assumed that come the colder weather they’d follow the chemical pheromone trail that previous incumbents had laid down and be jostling for the best positions in the corners above the windows as usual. But, no. They didn’t come!

Was ’something’ happening in the environment that was impacting Harlequins? Nature has a way of redressing the balances we upset, and researchers had discovered that existing native predators, such as a parasitic wasp that lays eggs on ladybirds, had turned their attention to this rather abundant newcomer. Could the larvae we found not made it to adulthood? Could a new disease have emerged as our summers begin to warm?

Who knows, and on a riff of the old ‘swallows and spring’ proverb, a few missing ladybirds does not a set of valuable data points make. It’s an anecdote and it may just be a very local response anyway. I tweeted back in January wondering whether anyone else had noted anything similar, but apparently not. So this entire post may be just me wittering on about something unimportant. On the other hand we can all be citizen scientists and put our sightings online anyway, just in case they’re useful (or just in case they’re useful and we get to scoop a huge cash prize in twenty years for being the first to spot a trend which was leading to the eventual extinction of the Harlequin Ladybird in the UK).

So (and back to reality) that’s the story of our non-sighting. Just in case. But has anyone reading this noticed a dearth of ladybirds holed up in their house this winter, too, or is it really just us?