Planet Earth Online

Aliens in the attic

Helen Roy

Centre for Ecology & Hydrology

"Ladybird knocks spots off the squirrel's migration" (The Times, 7th February 2008); "Invading ladybirds breed up ecological storm for UK species" (Guardian, 30th June 2009); "Harlequin ladybird threat to 1000 species" (Mirror, 30th June 2009); "Beware the plague of smelly ladybirds" (Daily Express, 27th October 2009)

These are just a few of the many headlines for stories about the arrival and spread of the harlequin ladybird (Harmonia axyridis). Indeed the press has been instrumental in highlighting research on the harlequin ladybird; last year alone there were more than 200 press items about the harlequin ladybird. But what is the story behind the headlines?

The invasive alien harlequin ladybird, Harmonia axyridis was introduced into continental Europe in the 1980s as a biological control agent. It's a voracious predator of scale insects (small sap-sucking insects, so called because they produce an umbrella-like waxy coating or 'scale' over their soft bodies) and aphids. Never intentionally introduced into Britain, it arrived in the county of Essex in 2004 and its spread across the country has been spectacular - approximately 100 kilometres per year.

The harlequin ladybird is particularly abundant in the southeast of England, but there are many records from central and northern England, Wales and also a few records from Scotland, as far north as Orkney. In the last month we heard that the ladybird is now breeding in Scotland.

This precise information on the distribution of the harlequin has been achieved because of the staggering response from people contributing to the harlequin section of the UK Ladybird Survey website which was launched in 2005 as a collaborative project between the Centre for Ecology & Hydrology, the University of Cambridge and Anglia Ruskin University.

People across the country have recorded their ladybird sightings and uploaded photographs, and this has resulted in an impressive and unique dataset documenting the movement of an alien species since its arrival in Britain.

Research behind the scenes of the ladybird survey has also been very productive. We have asked key questions to unravel the story of this alien invader. Perhaps the most important, but difficult to answer, is: how will this species affect native biodiversity?

Laboratory studies have demonstrated that the harlequin can eat native ladybird species such as the 7-spot, Coccinella septempunctata, and the 2-spot, Adalia bipunctata while these native ladybirds do not eat the harlequin. Further experiments have shown the ladybird also eats other insects such as the green lacewing, Chrysoperla carnea and even butterflies. In all of these cases it is usually the immature stages (larvae) that are attacked.

But what is happening outside the laboratory in the wider countryside? How can we address this challenging question? Every year ladybird numbers vary dramatically. Many people remember the year of 1976 when 7-spot and 11-spot, Coccinella unidecempunctata, ladybirds were extremely abundant. The summer of 2008 was bleak for all ladybirds but then last summer numbers were high.

So how can we tease out whether or not the harlequin is having an impact on native ladybirds against this backdrop of fluctuating numbers? One answer is: with difficulty! However, a more constructive response is to use standard survey methods to monitor ladybirds (and other insects) in various habitats throughout the year. Such systematic field surveys are indicating that the niche of the harlequin overlaps with a number of herbaceous and arboreal insect species.

These results allow us to assess the status of native species using ecological models which can include other factors such as habitat and climate. We can integrate the data received through the online survey to strengthen these models. In addition, the photographs from contributors to the UK Ladybird Survey indicate the potential for antagonistic interactions between the harlequin and other species (people have recorded H. axyridis eating larvae of many species, from ladybirds to lacewings and even moth larvae) and we can use these to refine our research questions.

Information of this kind is being gathered not only in Britain but also across Europe. Indeed, collaborative effort is essential to further our understanding of this conspicuous invader. So in September this year scientists from Europe, United States, Japan and South Africa met in Switzerland to share their findings.

The main conclusion so far is that the arrival of the ladybird in Europe poses a risk to native biodiversity, but we are not yet in a position to say how big this threat is. There is an early indication that the small 2-spot ladybird is being found less frequently than in previous years. Is this a consequence of the harlequin or was the species already in decline? This species will be the focus of extensive analysis over the coming years.

Each autumn the UK Ladybird Survey receives reports of very large numbers of harlequins, when the insect enters buildings to find suitable overwintering sites. The autumn of 2009 was no exception; the survey received approximately 800 records a week during October.

The 2-spot ladybird also favours buildings for overwintering and so now is an ideal time to look for these two species. Window frames and attics often harbour large aggregations and it would be very useful if people could send in photos of the ladybirds they see in their houses this winter using the online survey or perhaps their mobile phones (text* "ladybird" to 83040). How many harlequins are living in your house? How many 2-spots?

We are often asked what will stop this invader? We do not recommend anyone killing the harlequins they see because they are easily confused with other species and such action would have minimal impact on the overall harlequin ladybird population at large. Also, we do not yet have a full understanding of the threat posed to biodiversity by the harlequin.

There are a number of parasites that attack native ladybirds and this year we have the first evidence that they are beginning to turn their attention to harlequin ladybirds. This is a research theme that we will be expanding over the next year when we will be encouraging people to report their sightings of some of the parasites that exploit ladybirds. At the end of last year I received an exciting package - some harlequin ladybirds infected with an insect pathogenic fungus. This is the first such report from Britain but I am sure it will not be the last.

So to conclude, the harlequin ladybird is often reported as an invasive non-native species with far-reaching ecological impacts, and there is no doubt that it could threaten biodiversity. However, it is critical that we gather evidence to give us a thorough understanding of the extent of any effects it will have on other species. We have a unique opportunity to monitor this species through public participation and to study this species within a community context through extensive biological recording in the field.

*Texts will be charged at your standard network rate. Internet browsing costs will be subject to your tariff but should not be more than 20 pence.

Posted on 1 February 2010

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