From the website of the Norfolk Wildlife Trust:
“Harlequin ladybirds are the most invasive ladybird species on earth. Female harlequin ladybirds can begin to lay eggs five days after becoming an adult and a single female can lay over a thousand eggs in her lifetime.
The harlequin ladybird was introduced to North America in 1988, where it is now the most widespread ladybird species on the continent. It has already invaded much of northwestern Europe, and arrived in Britain in summer 2004.
There are 46 species of ladybird (Coccinellidae) resident in Britain, and the recent arrival of the harlequin ladybird has the potential to jeopardise many of these.
The harlequin ladybird was first recorded in Norfolk in 2004. Since then it has rapidly increased in number and distribution.
If you think you’ve found a harlequin ladybird then please send a record of your sighting to the Ladybird Survey. Details of how to do this, and a form to download, can be found on their website at https://www.coleoptera.org.uk/coccinellidae/home .
The harlequin is a non-native species which has become a pest in the UK, causing a decline in some of our native ladybird species as it out-competes its smaller rivals for food, and preys on their larvae. Since its arrival in Britain in 2004, it has spread rapidly across the southeast and is gradually moving north and west. Monitoring its spread across the country is essential. The important information you need to send them should include your name and address, what you found (adult, larvae, pupae etc), where you found it (a grid reference and location is best but a postcode will also do), the date when you found it, how many you found (1, 2–5, 6–10, more than 10) and what they were doing – e.g. nothing, walking, laying eggs, mating, eating etc. A photograph would be useful as well (but not essential) and digital photos can be submitted on-line.
Harlequin ladybirds can be difficult to identify as they are highly variable in colour and ‘spottiness’. They range from orange or red with black spots to black with red or orange spots. They also have various white markings on their head and the bit behind their eyes (the pronotum). The number of spots is also highly variable.
While many of our native ladybirds can also vary in colour and number of spots – especially the two- and ten-spot ladybirds, harlequin ladybirds are larger than most of them (>5.5mm). The exceptions to this are the seven-spot, scarce seven-spot and eyed ladybirds which are a similar but they have black legs instead of reddish-brown like the harlequin. The harlequin is a non-native species which has become a pest in the UK, causing a decline in some of our native ladybird species as it out-competes its smaller rivals for food, and preys on their larvae.”