Ladybirds play the villain

While it made a change from reading seemingly endless headlines about the credit crunch and the ‘will they, won’t they’ story of the ashes, recent coverage of the ladybird ‘invasion’ was nonetheless disheartening. In many ways it simply reinforced my view that we seem incapable of tolerating the natural world around us whenever it steps over the line beyond being simply a convenient backdrop to our daily lives.

The spectacle of many millions of 7-Spot Ladybirds concentrated along the coast of Norfolk should be something to marvel at, a mass of coleopteran life rarely seen in this country. Instead it was viewed as a threat, something that might keep the tourists away, curtail the summer and further deepen our economic gloom. Alarmist headlines, such as the Independent’s ‘Ladybird invasion hits Norfolk’, were matched by comments like ‘it was quite horrific’, ‘it ruined our visit’ and ‘there was absolutely no escape from them’. Still, at least we didn’t stoop to the levels seen in 1976 when far larger numbers were present, with cartoons showing ladybirds with teeth and, unbelievably, Nazi swastikas in place of spots. At worst, the presence of so many ladybirds was an inconvenience.

As was the case with the 1976 outbreak, the origins of the ladybirds involved this summer are somewhat unclear. Were they, as some have argued, immigrants blown in from the near Continent or were they home-grown ladybirds, the product of a good breeding season? I favour the latter explanation, in part because it follows the well-reasoned case made by the late Michael Majerus when explaining the origins of the 1976 occurrence. A successful breeding season last year, followed by a fairly mild winter and, importantly, a superabundance of aphids during the early part of the year would have enabled the 7-Spot Ladybird population to reach better than usual levels. A sudden decline in the aphid population, possibly weather-related, would have left the ladybirds devoid of a food supply, prompting them to move on. Those reaching the open sea would have turned back, to congregate on the coast where they covered boats, fence posts and other surfaces.

Look at photographs of these gatherings and you will notice that virtually every last individual is identical, such is the lack of variation seen in this particular species. This may seem like a fairly obvious statement, but many ladybird species show a great deal of variation in their appearance. Melanic forms are common and the number, shape and size of spots can vary considerably from one individual to another; counting spots will not necessarily help you to identify the species!  Rather than moan let’s celebrate a bumper year for this normally popular insect.

Harlequin poses threat to natives

Over the last few days I have spotted an increasing number of harlequin ladybirds. Normally I would be delighted to see a ladybird but the harlequin is not one of our native species. Instead, it is a potentially troublesome and invasive addition to our fauna, reaching our shores because of our own actions. Let me explain. The harlequin ladybird is a native of eastern Asia but it has been introduced to a number of countries as a biological control agent. Scientists, looking for an alternative to pesticides, have used the harlequin to control crop pests, such as aphids and scale insects, by introducing them into glasshouses, crops and even gardens. Unfortunately, as has been the case for a number of species used in this way, the harlequin has gone on to become a pest in its own right. It first established itself here in Britain in 2004, with individuals arriving from the Continent (where they had been introduced) thanks to their remarkable powers of dispersal or by gaining assistance in shipments of plants and other foodstuffs.

The harlequin ladybird is pretty catholic in its choice of habitats but does seem to favour deciduous trees like sycamore and maple. Here it feeds on aphids, scale insects, the eggs of various moths and a range of other insects. This species has a clear competitive advantage over most of our native ladybirds because it has a much greater breeding potential. The pre-adult stage lasts just 20 or so days (although this is temperature dependent) and, once they reach adulthood, the females can begin to lay eggs after just five days. This means that a single female can produce more than 1,000 eggs during her lifetime.

At the moment, the numbers of harlequins in Britain have not reached the pest proportions seen elsewhere in the world. In North America, many tens of thousands may overwinter in a single home and, given their tendency to bite, they are not the most welcome of lodgers. They are also a threat to our native species, especially when aphid numbers are low, as the species is likely to feed on other ladybirds and their larvae. Even wine production could be threatened. Harlequins are attracted to soft fruit, like grapes, and may occur in such numbers that they taint the resulting wine production with the alkaloid chemicals they carry to deter potential predators.

Fortunately, the Government has provided funding to the Harlequin Ladybird Survey Project (see www.harlequin-survey.org) to collate information on sightings and to undertake research to assess the level of the threat. It is also hoped to determine how the species may be controlled to prevent it becoming a pest. Let’s hope the research comes up with a solution.