Ten Years of Invasion how the harlequin spread

Published: 20 May 2015 at 16:24

New report shows that only Scotland has stood firm against alien ladybird species

The history of how the harlequin ladybird – an insect described as “the most invasive ladybird on Earth” – has spread so successfully across mainland Britain over the last decade, has been published today in the journal Ecological Entomology.

Ten Years of Invasion is co-authored by Dr Helen Roy of the Centre for Ecology & Hydrology and Dr Peter Brown of Anglia Ruskin University.

The harlequin ladybird (Harmonia axyridis) was first recorded in the South East of England in 2004 and thanks to the public submitting over 30,000 recordings to the UK Ladybird Survey since 2005, scientists have plotted its spread in a northerly and westerly direction across mainland Britain.

The research, which examines the factors for its incredible progress, shows that only Scotland has stood firm against the invasion, thanks to its climate (lower temperatures and higher precipitation than England) and less favourable habitats, such as heathland and moorland. 

Originally from Asia, the harlequin has proved particularly successful in urban areas, and almost all Scottish recordings have been in towns or cities. 

Human involvement also appears to have been key to their spread.  For example, the first harlequin spotted in Scotland (in 2007) was a result of the ladybird being transported in a suitcase; while the first record from the Orkney islands (in 2008) involved the ladybirds being transported with vegetables from mainland Britain.  Such inadvertent human assistance can greatly increase the rate at which invasive species expand their ranges.

The harlequin outcompetes and directly feeds on other ladybirds, and appears to have played a large part in the decline of species.  Since its arrival in 2004, seven out of eight native ladybird species tested have seen a decline in numbers across Britain.

The report concludes that although the harlequin is currently less susceptible to attack by native parasitoids and pathogens than Britain’s native ladybirds, within the next 10 years it is possible that natural enemies will begin to adapt.

Dr Peter Brown, Senior Lecturer in Zoology at Anglia Ruskin University, said:

“Much of the research on this species would have been impossible without the thousands of people who have taken part in the UK Ladybird Survey.  The result is a unique dataset tracking the invasion of a non-native species from the moment of arrival.
“This new paper brings together all of the research on the harlequin ladybird over the last 10 years and highlights the factors, such as adaptability to climate and habitat, that have allowed this species to become one of the most successful global invaders.

Dr Helen Roy added:

“The commitment of people to recording harlequin ladybirds has encouraged the development of a recording system for other non-native species which is being used as an early warning tool for the Asian hornet and other species that are on the horizon.”  
“The number of new arrivals is increasing year on year and so the demand for scientific evidence to underpin our understanding of the impacts of invasive non-native species on other wildlife will continue to be high.”