The invasion of the ladybirds

Aliens are invading the United Kingdom and the consequences may be far reaching.

The non-native harlequin ladybird Harmonia axyridis has rapidly spread throughout Europe and is now displacing native species in the UK.

Researchers at Anglia Ruskin University in Cambridge have been tracking the invasion. They examined changes in ladybird communities at four sites (two lime tree sites, one pine tree site and one nettle site) in East Anglia, England, over an 11-year period (2006–2016).

Harlequin Ladybirds displacing native species

Their study, published in the journal Insect Conservation and Diversity shows that overall Harlequins represented 41.5% of all ladybirds sampled in 2006 to a high of 70.7% and was over three times more abundant than the second commonest species, Coccinella septempunctata.

The proportion of native ladybirds declined from 99.8% in 2006 to 30.7% in 2016, although Halequins were dominant only at the lime tree sites and not at the pine or nettle sites.

In an earlier study the researchers reported declines in three native species over a 3-year period following the arrival of harlequin ladybirds in East Anglia. Their current work confirms and extends that finding.

Does it matter?

A key question is whether any of this matters. Isn't one ladybird much like another? The answer is that it matters at several levels, both in what it represents and in its consequences. Nor is it the case that 'one ladybird is like any other'.

Ladybird communities in a given habitat often comprise a small suite of species that co-exist by occupying different niches. Some will feed on aphids, others on mites, still others are herbivorous.

It matters also at another level.

The spread of invasive species

Global trade, travel and climate change are driving the spread of 'invasive species'. Invasive non-native species are widely acknowledged as one of the main causes of biodiversity loss globally. The prevalence of such invasions has increased dramatically over the course of the last half-century.

As the climate warms, this enables alien species to spread further to regions where previously they were poorly adapted. Barriers to such movement are being eroded. Such invasions can occur quickly, outpacing the adaptability of the native species. Whilst native species struggle to adapt to changing climate conditions, the invasive species takes hold. The population explosion of an invasive species can then disturb the predator-prey balance by providing a new abundant food source for the predators. Increasing numbers of predators then further disturb the precarious hold of native species.

Economic costs

So, why does it matter? We could answer that question in monetary terms. It is estimated to cost the global economy some $70 billion annually. Many of the invasive species become 'pests' to agriculture. But the real cost is greater than can be measured in dollars.

Human cost

Biological invasions are a major threat to global food security and livelihoods, particularly in developing countries. Those countries with high levels of subsistence and smallholder farming, often lack the capacity to prevent and manage biological invasions.

Ruined crops mean ruined lives. This can then become a driver for human migration as the land ceases to sustain a growing population.

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