The ladybirds can form large clusters typically around window frames. © Peter_Fleming / Shutterstock
A non-native beetle, the harlequin ladybird was introduced to the UK as a form of natural pest control. They hang out in swarms, gather around our windows, eat other ladybirds and carry a sexually transmitted disease (STD).
In spring and autumn, you might suddenly see lots of these ladybirds about. But just how dangerous is the harlequin and why are they in your home?
Max Barclay, our Senior Curator of Beetles, explains why you don’t need to be worried about these ladybirds and what to do if you see one.
Ladybirds belong to the family of beetles known as Coccinellidae, of which there are at least 3,500 species worldwide.
In the UK there are 46 native species. Of these around 26 colloquially are called ‘conspicuous’ ladybirds. They tend to be brightly coloured, with many sporting the classic red-and-black polka dot. The remaining 20 species, called ‘inconspicuous’ ladybirds, are often drab in comparison.
Harlequin ladybirds, Harmonia axyridis, are not native in the UK. They live naturally in eastern Russia, China and Japan, but likely arrived in Britain in 2004 as natural pest control via either Europe or the USA, where they were first introduced as a biocontrol agent for aphids and scale insects.
They can now be found not only in Asia, Europe and North America, but also South America, southern Africa and New Zealand.
Harlequin ladybirds are incredibly variable, but the easiest way to identify them is by their orange legs. Image © entomart via Wikimedia Commons
“Harlequin ladybirds are pretty distinctive, even though they have lots of colour forms,” explains Max. “You can find different varieties, from red with black spots, to orange ones and even black ones with red spots.”
The harlequin ladybird is one of the most variable ladybird species in the world. They tend to be around the same size or slightly larger than the more familiar native seven-spot ladybird. Like the seven-spot they also have two white spots on their thorax.
But there’s one key difference that allows you to identify a harlequin ladybird.
“Whereas the native ladybirds are black on the underneath and have black legs, most of the harlequin ladybirds are orange on the underneath and have orange legs,” says Max.
As the weather begins to cool, many species in the northern hemisphere begin to wind down and start preparing for hibernation.
All species of ladybird in the UK hibernate – in insects, this is technically known as diapause. This is part of the lifecycle of ladybirds, which hatch from eggs in summer and grow into their adult form by winter. They then hibernate during the colder months, before emerging in the spring when they mate, lay their eggs and then die.
Harlequin ladybirds would normally hibernate in caves and hollow trees, but have found that the inside of homes are a good alternative. © muroPhotographer / Shutterstock
The adults of some species will hibernate on their own as they find cracks in bark or rocks in which to hunker down for the cold winter months. But other species, such as the harlequin, will hibernate together.
“There are a number of species of ladybirds that hibernate in big clusters,” says Max. “Ancestrally harlequin ladybirds would probably have hibernated in big clusters in caves, hollow trees and other sheltered places.”
In the absence of these they may well try and gain entrance to your home. The easiest way for them to do this is through the small gaps along the edges of loose-fitting windows. It’s common to find them in your home, but there’s no need to kill them as they’re harmless.
“These ladybirds don’t want to be in your home any more than you want them there. If people squash them, they can stain walls with their defensive yellow chemical secretions which can be slightly smelly.”
The best thing you can do is “to help them find their way out,” Max adds. “The ladybirds will be grateful and may even repay the favour by eating some of the greenflies on your roses.”
Harlequins have attracted negative publicity since they were introduced to Britain.
This is partly because they’re known to reproduce quickly, gather in large swarms and compete with native ladybirds for aphids. In addition to consuming the larvae and eggs of other ladybirds, they also engage in cannibalism. But in recent years the population of harlequin ladybirds shows signs of being brought under control by disease and native predators.
The harlequin ladybird is known to carry a sexually transmitted disease that forms a white crust on their exoskeleton. © Jeremy David Rhodes / Shutterstock
Harlequins can also carry an STD called laboulbenia. It’s a fungus that forms little scales on the wing cases and sometimes white crust on parts of the exoskeleton which can be seen with the naked eye. The STD also infects native ladybirds, and the harlequin is simply another host for the fungus to live on. The good news is humans can’t be infected.
“That is ridiculous,” laments Max. “It’s a fungus that grows on the exoskeleton and we don’t have one of these. Also, we don’t have sex with ladybirds.”
Occasionally, a ladybird will bite humans if provoked, but it’s harmless and causes no more than a minor irritation.
Currently, harlequin ladybirds are widely found throughout England and Wales, though they’re slowly pushing further north into Scotland.
While the ladybirds are thought to have a limited impact on some native species, they’re now so well-established that they’re effectively here to stay. Some native predators of the insects, such as a parasitic wasp that lays eggs on the ladybird, have started preying on them. This means that harlequin ladybird numbers are expected to reach some form of equilibrium.
“These aren’t anything to panic about,” stresses Max. “First of all they can’t give you diseases, they can’t hurt you and they’re not going to completely exterminate our native fauna. They’re going to find some kind of balance, even if that includes them in reasonably large numbers.”
So, if you want to stop these insects from entering your home, just make sure your doors and windows are fully sealed and insulated.
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