Every autumn, householders report clusters of ladybirds on window frames or small grey creatures on a kitchen floor and ask whether a pest controller is needed. This article summarises the Royal Horticultural Society (RHS) advice pages “Harlequin ladybird” and “Woodlice”. It concerns Britain, where the RHS says the harlequin ladybird is now widespread in England and spreading in Wales, Scotland and Ireland. Not every pest question needs a treatment; these two are examples where the RHS advice is to tolerate or remove by hand. This is general information, not a substitute for professional identification.
What a harlequin ladybird is
The RHS says the harlequin ladybird is one of about 40 species of ladybird found in Britain and Ireland, is predatory and prefers aphids but will eat other insects. It originates from Japan and has been introduced around the world as a biological control agent against aphids. The RHS says it was not deliberately introduced to Britain or Ireland but became established in 2004. Adults are 8 to 10mm long and very variable in colour; the two most common forms are black with two red spots or orange with 18 black spots. Some native ladybirds also have many colour forms and can look similar, so identification is often not easy. The RHS notes that the native two-spot and ten-spot ladybirds are small, at 4 to 5mm. Sightings can be submitted to the UK Ladybird Survey.
Why they gather in buildings
According to the RHS, many ladybird species like to overwinter in groups inside buildings, and the harlequin is no exception. In autumn adults seek overwintering sites and can form large aggregations, which can become particularly evident on the south side of buildings and other structures. The RHS says the appearance of large groups indoors can cause some concern but that there is no danger associated with their presence, although they can exude a clear yellow liquid that may stain furnishings.
What can and cannot be done
The RHS states that it is not possible to discourage ladybirds from entering buildings, and that the ladybirds can be captured and removed or tolerated. For control, it says there are no means of controlling harlequin ladybirds, since any action would also harm native ladybirds, other aphid predators and other insects, and because they are now so well established and abundant that destroying a few in one area will not make any difference to overall numbers. For buildings, it advises that they can be tolerated or captured and released outdoors. The site’s article on cluster flies in lofts looks at another autumn insect that overwinters in buildings, and its guide to pest products as biocides covers what a product label means.
The ecology point
The RHS says a harlequin ladybird can be considered a useful addition to the garden because it feeds on aphids, but that it will also eat scale insects, the eggs and larvae of butterflies and moths, other small insects, other ladybirds and even its own kind. The RHS says there was a fear that it would out-compete native aphid predators, that evidence in Britain is so far mixed, and that research is ongoing.
Woodlice indoors
The RHS says there are 30 species of woodlice in Britain, five of which are often found in gardens. They are terrestrial crustaceans that shelter in dark, damp places, especially where decaying plant material accumulates, and feed largely on damp decomposing plant material, which makes them part of the garden’s nutrient recycling. They are up to 1cm long and often grey, and some species, known as pillbugs, can roll into a ball when threatened. During the day they hide under logs, stones and flower pots and at night they move around looking for food.
On damage, the RHS says woodlice do not usually damage healthy plants but can become associated with damage that has other causes, such as slug damage or plants that have died and begun to rot. It says they occasionally damage very soft tissues such as seedlings and sometimes strawberry fruits, and that holes in older, tougher plant material will have been caused by something else such as slugs or caterpillars. Its management advice is that they are a vital part of garden biodiversity and should be encouraged in a healthy garden, that they are naturally abundant, and that they are food for shrews, toads, centipedes, some spiders, ground beetles and parasitoid flies.
The RHS says that woodlice can come into houses from gardens but are unlikely to survive for long indoors unless they find a damp place to shelter. Repeated sightings inside can therefore be a clue to a damp area. The site’s article on silverfish and moisture indoors discusses a similar link between a damp home and insects.
Common questions
Are harlequin ladybirds dangerous?
The RHS says there is no danger associated with their presence indoors, although a clear yellow liquid they exude may stain furnishings.
Can I stop them coming in?
The RHS says it is not possible to discourage ladybirds from entering buildings; they can be captured and released outdoors or tolerated.
The bottom line
The RHS advises tolerating harlequin ladybirds indoors or releasing them outside, because they cannot be controlled without harming other insects, and treating woodlice as harmless garden recyclers that only linger indoors where it is damp. Neither, on the RHS’s account, calls for treatment.
Sources
- Royal Horticultural Society, “Harlequin ladybird” (rhs.org.uk)
- Royal Horticultural Society, “Woodlice” (rhs.org.uk)