Harlequin ladybirds in the house: how to identify them and keep them out

As the weather cools in autumn, many homes start to see ladybirds gathering on warm, sunny walls and around window frames, then turning up indoors in corners, on ceilings and in light fittings. These are usually harlequin ladybirds, an invasive species looking for somewhere to spend the winter.

01What is a harlequin ladybird?

The harlequin ladybird (Harmonia axyridis) is native to eastern Asia. It was introduced to parts of Europe and North America to control aphids, and from there it reached Britain, where it was first recorded in 2004. It has since spread across much of the country.

It is a concern for wildlife because it competes with native ladybirds for food and also eats their eggs and larvae. Indoors, it is a nuisance rather than a danger.

02How to identify them

Harlequins are hard to identify by colour alone, because they come in many forms: orange with lots of black spots, red with a few, black with two or four red or orange patches, and more besides. A few things help:

• Size. At around 7 to 8mm, they are a little larger and rounder than most native ladybirds, including the familiar seven-spot.
• Legs. Harlequins usually have brown or orange legs. The seven-spot has black legs.
• Behaviour. Large clusters on buildings and indoors in autumn are typical of harlequins.

Native ladybirds sometimes shelter in buildings too, so if you are not sure what you have, a clear photo helps.

03Why are they all over my windows?

In autumn, harlequins go into a resting state for the winter and look for dry, sheltered, sun-warmed crevices. Window frames, soffits, eaves, gaps in brickwork and loft vents all suit them. Once a few settle, they give off scent signals that draw more in, which is why numbers can build quickly on a sunny autumn afternoon. From there, small gaps let them into the house, where they gather on ceilings, in light fittings and behind curtains. On mild winter days some wake up and wander about.

04Are they harmful?

Not seriously. They can give a small nip if handled. When disturbed or squashed they release a yellow, strong-smelling fluid, known as reflex bleeding, that can stain paintwork, curtains and soft furnishings. Some people report mild skin irritation or allergy-type symptoms.

05Keeping them out

• Seal the gaps. Focus on window frames, door thresholds, loft hatches and gaps around pipes and cables, using a suitable exterior-grade sealant.
• Mesh vents. Fit fine insect mesh to air bricks and soffit vents, keeping the airflow they are there to provide.
• Close blinds or curtains on sun-facing windows on bright autumn days, which makes them less attractive.
• Keep frames and sills clean so that early clusters are easy to spot and remove.
• Check the loft and upper landings in autumn, and deal with small clusters before they grow.

06If they are already inside

Do not squash them, as that causes the staining. Use a vacuum cleaner to remove them, and empty the bag or cylinder outside straight away to avoid the smell. Household insect sprays indoors are not a good idea: they are often ineffective on clusters tucked into crevices and add exposure you do not need.