Q What are harlequin ladybirds?
A The harlequin is a relatively large ladybird with many colour variations, which has only recently started to appear in Britain.
Caption: Harlequin ladybirds help gardeners by eating pests such as aphids
Q Do they differ from other ladybirds?
A Worldwide there are about 3500 species of ladybird, 46 of which are resident in the British Isles.
Most of our ladybirds feed on other insects, though a few eat plants or fungi. Perhaps the most familiar is the seven spot (Coccinella septempunctata), a red ladybird with seven black spots. Some species can be difficult to identify as they vary a lot in colour. For example the two-spot ladybird (Adelia bipunctata) can be red with two black spots, or black with four red spots.
Other ladybirds may be yellow and black or brown and cream. There are good photographs of the 20 most prominent species of harlequin ladybird in Britain on the ladybird survey website (ladybird-survey.org or on harlequin-survey.org).
Harlequin ladybirds (Harmonia axyridis) are larger than most of our native ladybirds, reproduce more quickly, and are more voracious predators than many other species.
Q Where do they occur?
A Harlequins first started to appear in Britain in Essex in 2004. Their arrival provided an ideal opportunity for scientists to record the spread of an invasive alien species and they have been carefully monitored ever since.
Although most sightings are for the south and east of England, they have now been recorded over most of the country, including the tip of Cornwall and the far north of Scotland.
Q Where have they come from?
A Harlequins are native to parts of Central Asia and the Far East, in a band stretching from Kazakhstan to Japan. They were introduced into several European countries in the 1980s as biological control for scale insects and aphids. They were not brought deliberately to Britain, but turned up anyway, carried on cargo, vehicles or wind currents.
Q Why are they a problem?
A Harlequins are not a problem to gardeners; in fact, like other ladybirds they are an ally in the war against aphids and other insect pests.
However they could be damaging to our native ladybirds in two ways. Firstly because they are large and aggressive, they will actually eat other ladybirds especially their larvae, so could pose a threat to less common species. They are also likely to compete with our ladybirds for food.
All ladybirds can nip, though not break the skin, and may come into houses to hibernate in winter. These irritations seem to be more of a problem with harlequins, perhaps because they are larger, or sometimes occur in large numbers.
Q How do I recognise them?
A Harlequins are relatively large (6-8mm), quite round and domed. The wing cases can be pale yellow-orange, orange-red, red or black. They can have any number of spots from 0-21, or a grid pattern, in black or orange-red.
The most common variants in the UK are orange with 15-21 black spots or black with two or four orange or red spots. The harlequin survey website mentioned below has illustrations of 24 colour variations.
Q What is their life cycle?
A Most ladybirds overwinter in a dormant state between October and February. They become active and start feeding in March, then mate and lay eggs in June or July. The eggs hatch into larvae which are dark grey with black legs and heads. These pupate in July/August, to emerge as adults in August/September. There is now evidence that harlequins can go through this life cycle two or three times a year.
Q Will they wipe out our native ladybirds?
A The short answer is it is too soon to tell. The harlequin is certainly very invasive and adaptable. Harlequins were introduced into North America for biological control purposes in 1988 and are now the most widespread ladybird on the continent.
In Britain, ladybird populations fluctuate naturally a great deal from year to year and it is difficult to separate out the various factors responsible. Two-spot ladybirds are certainly declining, but this may or may not be anything to do with the recently arrived harlequins. Although they have been very fast and successful colonisers, there is evidence that they are now falling prey to some of our ladybirds' natural enemies such as insect-killing fungi, which could help keep the population in check in the long run.
Q Should I tell anyone about them?
A Since the harlequin invasion, ladybird numbers and distribution have been the subject of a number of research projects, and these are interested in sightings of all ladybirds, not just harlequins. You can even send in your records and photos by mobile phone. For more information, go to the website ladybird-survey.org or harlequin-survey.org
Q What other action should I take?
A There is no reason to kill harlequins. The loss of a few adults will make little difference to their numbers and, as they are not that easy to identify, you run the risk of killing a rare native species by mistake.