Ladybirds are great for your allotment and should be encouraged. I have had loads on my allotment this year. Ladybirds eat aphids which makes them exceptionally useful.
If you are interested in finding out which types of ladybird you have on your plot try the UK Ladybird Survey website. This website has a wide variety of information included on it and aims to help the recording of ladybirds within the UK.
The Harlequin ladybird is not native to the UK and is causing problems for our own native species due to it being the worlds most invasive species. To find out more, including how to identify and record sightings of the Harlequin ladybird, go to the Harlequin Ladybird Survey website.