As one publicity slogan goes: ‘Everyone loves a ladybird’. Well, if we do, it is surely time to give them a little thought and care. A nineteenth century ‘Ladybird, ladybird’ children’s nursery rhyme from Dorset runs:
Laedy-bird! Leady-bird! Vlee away home,
Your house is a-vire, your children will burn.
In some ways, the whole world is on fire. By our manipulation of our environment, our destruction of natural habitats and our ever-increasing need for food and space for our multiplying numbers, we are giving ladybirds nowhere else to go.Michael Majerus, A Natural History of Ladybird Beetles
Harmonia axyridis, or the harlequin ladybird, was first seen in the UK in 2004 and has since spread over the country. It has been single-handedly blamed for causing the decline in Britain’s native ladybird populations, and is even said to sting and carry STDs – Twitter is full of people worrying they may get an STD from a ladybird. As they look for places to hibernate, the Harlequin ladybirds have become notorious for forming large groups inside houses, especially on windows and door frames. You might have noticed this happening to your house. Terrible isn’t it? Since harlequins arrived in the UK in 2004, media coverage has resulted in what’s been described as ‘a complete condemnation of this Ladybird’.
Yet while the threat to some native UK species is very real, coverage of the harlequin’s arrival in the UK has been sensationalised, and false myths are being spread, which may result in further environmental damage amid a very serious decline in the insect population. Harmonia axyridis is itself an intriguing little critter, with one of the most advanced immune systems of any insect, and the potential to be a source of new drugs due to this inbuilt resistance. This article will discuss why we should welcome our spotty overlords, or at least not do anything to harm them.
Like other beetles, ladybirds have hard wing-cases (elytra). They also have a round or oval body, with the pronotum, the section between the insect’s head and its elytra, wide and often patterned. Ladybirds have clubbed antennae and six short legs; their feet have four segments, but one is often too small to be visible. When threatened, hibernating or sleeping, ladybirds withdraw their legs and antennae under their bodies, so they appear dead. Coccinellids also exude foul-tasting or poisonous defensive fluids from their legs and the side of their bodies when attacked, an ability known as reflex bleeding. Their bright colours and spots signify their toxicity and warn other animals not to eat them. Other defence mechanisms also exist, like camouflage and dropping off plants in response to movement.
Ladybirds often prey on garden and agricultural pests, one obvious example being aphids; one seven-spot ladybird will live for around a year and eat about 5000 aphids in its life; the adult beetle can eat up to 90 per day. However, some species eat mildew, such as the tiny yellow 22-spot ladybird, and a few eat plants, such as the 24-spot. Not all ladybirds are red and black; the two-spot frequently comes in a black form with red spots; the orange ladybird is orange with white spots, and there are even striped ladybirds. There are many small beetles which aren’t brightly coloured, but still feature characteristics like the typical coccinellid shape – these are known as ‘inconspicuous ladybirds’.
Some people have taken the fact that harlequin ladybirds are an invasive species to mean they should kill them. But harlequins have hundreds of different colour variations, although they have a few shared characteristics such as brown legs, a rounded shape and usually an M-shaped marking on the pronotum. Some of these forms are extremely similar to existing UK species. For instance, black forms of Harmonia axyridis may look extremely similar to pine or kidney-spot ladybirds. The cream-streaked ladybird, Harmonia quadripunctata, is closely related to the harlequin and looks similar, as do rarer ladybirds such as the thirteen-spot, once thought to be extinct, and the eyed ladybird. So any time someone kills any ladybird, they could be killing something already under threat.
It is worth explaining how harlequin ladybirds ‘invaded’ the UK. They are native to Eastern Asia and Japan, hence their American name, the ‘Asian Lady Beetle’. They were imported to North America and parts of Europe as ‘biological control agents’ to be used on crops to eat aphids and other pests. Harmonia axyridis was particularly suitable because it is a voracious predator of aphids, eating at least 5500 in its lifetime, more than our native seven-spot. It is adaptable to a wide range of climates, with specimens recently being found in parts of Africa. And it’s not just restricted to aphids, consuming scale insects and the larvae of flies and small moths
And this is the problem. The harlequin ladybird is a killing machine, that can and will eat almost anything – including other ladybirds. This isn’t unusual; the average ladybird larva will eat the larvae and eggs of other ladybirds and even its own species, if there is nothing else to eat. Many species choose to lay their eggs away from any other ladybird eggs, because they might get eaten. As one article I read for this piece made very clear, the world of insects is brutal – you can get eaten (or squashed or parasitized) at literally any time. When the contents of seven-spots’ stomachs were analysed in Germany1, many of them contained the larvae of other ladybird species, and some studies indicate that two-spots who eat the eggs of other two-spots as larvae are healthier as adults.
Harlequins therefore aren’t unusual in eating other species of coccinellid. However, all harlequin ladybirds contain fungi called microsporidia which are passed on to the eggs by the adults. Microsporidia have no proven effect on Harlequin ladybirds – they may have a symbiotic relationship, as with humans and some species of bacteria. But other ladybirds which eat harlequin eggs and larvae get sick and die – in one study, every seven-spot which ate harlequin larvae died.
The toxic chemicals inside any ladybird will protect it from predators, with the seven-spot being one of the most well protected. A grotesque experiment in the early 90s showed that blue-tit chicks fed a diet of seven-spots became seriously ill or died in a matter of days. Birds almost always avoid ladybirds, and although the beetles frequently get caught in spiders’ webs, they are not always eaten. However, some spiders reportedly suffer no ill effects from eating harlequin ladybirds. And while harlequins and others do carry STDs, they only affect other ladybirds, so humans are in no danger of catching them – something which is seldom clarified in the press, because then there wouldn’t be a story!
One of the most common predators of coccinellids is Dinocampus coccinellae, a small wasp with a horrifying lifestyle. It injects its egg into a ladybird, and the larva then hatches and feeds off its host, before emerging from a cocoon beneath its still-living body. Only around 25% of ladybirds survive this experience, and in some areas almost all seven-spots are affected by this parasite. Harlequin ladybirds fall victim to Dinocampus coccinellae at a lower rate than the seven-spot and many other native species of ladybird in the UK, and parasitisation is still considered quite unusual. Some studies suggest that Dinocampus larvae are often killed by this ladybird’s powerful immune system. This gives Harmonia axyridis a big advantage and increases the pressure on native ladybird populations.
Even two-spots (Adalia bipunctata), usually not preyed on by Dinocampus wasps, often find themselves outcompeted for food by harlequins, especially because their breeding seasons coincide and they compete for food on the same plants. Out of all the native species affected by the rise of this ladybird, the two-spot has declined the most dramatically; the UK population of two-spots has fallen by 44% since the harlequin ladybird was first spotted here. Harlequin ladybirds can also breed almost continuously, whereas most UK ladybirds only breed once or twice a year, leading to even more competition.
Harmonia axyridis can survive in a huge range of habitats, but many native UK species are not as well equipped to handle changes in temperature and humidity. Some ladybirds need a period of hibernation before they can breed. Thus increasing temperatures can also affect their fertility; harlequins do not need this period and in mild winters in some regions can breed up to five times a year. The late entomologist Michael Majerus saw the invasion of species such as the harlequin ladybird as an example of ‘biotic homogenisation’, which means that habitats around the world are becoming more homogenous with the accidental or intentional introduction of invasive species into the ecosystem, and the resulting decline in biodiversity and loss of rare animals and plants.
But you cannot entirely blame harlequins for reducing other insect populations, when they are just ‘ladybirds being ladybirds’. This beetle may be one factor in the decline of other species, but equally, if not more important, are the effects of climate change, pollution and habitat destruction. The number of insects has decreased so much that there is talk of an ‘insect armageddon’, which may take the planet millions of years to recover from – and anything which relies on insects for food will be affected. In his 2012 book A Natural History of Ladybird Beetles, Majerus described ‘ladybirds’ greatest enemy’ as a ‘professed friend of ladybirds – us!’
One example in which humans have become an enemy of ladybirds is that of climate change. If they are woken up by warm temperatures in the middle of winter, or earlier than usual, they may be unable to find prey and then starve to death. Conversely, ladybirds can also freeze to death in the event of a short, unseasonal cold snap they haven’t been able to prepare for. And UK winters are becoming increasingly chaotic and unpredictable, with cold snaps in the middle of the autumn followed by warm periods, or very mild warm winters without a cold period at all. As ladybirds lie dormant during the winter, long periods of wet weather place them at risk of fungal infections, which are often fatal for an insect.
While the Harlequin ladybird has had a very negative effect on some species, such as the two-spot, others are less affected – perhaps because of their ability to adapt or feed from a variety of habitats. Others live in special habitats, such as in reed beds in water, in pine trees or alongside nests of ants, such as the scarce seven-spot ladybird. However, these are less in danger from the harlequin than they are from human activity, such as pollution and destruction of their habitat. The scarce seven-spot ladybird has adapted to living near wood ants, but their nests are often destroyed or severely disturbed, meaning the ladybird’s lifestyle is disrupted too. In areas where harlequin populations are more established, the populations often ‘swing back into an equilibrium’, although native species initially do suffer losses.
The harlequin ladybird may even end up being good for humans in unexpected ways. Harmonia axyridis has one of the strongest immune systems of any insect, which helps it to colonise new habitats rapidly without a huge risk of dying from infection. While researching what made this ladybird so successful in new environments, one team of scientists found that the fluid inside it contained more than 50 different anti-microbial peptides, or chemicals which protect the ladybird against infections – more than any other insect. Some of the chemicals found in the beetle are effective against malaria and even cancer – for this reason, it has been identified as a possible source of new drugs. They do sometimes seem more advanced than some other species, or at least more prone to being cautious and alert.
So what can one do to help ladybirds and other insects which may be under threat? One thing people can do is try not to panic every time they see an unusual insect, let alone kill it. Part of this problem is exacerbated by the media; recently several schools were closed in London because of groups of harmless spiders which had been the subject of exaggerated news articles. If you haven’t seen a certain insect before, it could just be very rare. If you have kids you may want to talk to them about this subject by, for example, getting them a book on insects. Practical things one can do include planting flowers to attract ladybirds and leaving a part of the garden untidy so as to provide a place for ladybirds to hibernate and live.
The harlequin ladybird itself may not be as bad as it’s pointed out. Many different species can be invasive in the right (or wrong) habitat, and even the well-loved 7-spot has had a negative impact on North American ladybirds since it was introduced there a few decades ago. The harlequin ladybird’s variability and ability to adapt to new situations are a huge part of its success, and in the future the chemicals it produces could be used to treat diseases such as malaria. Harmonia axyridis may help humans in more ways than just eating aphids in the garden – which it is exceptionally good at, despite its invasive behaviour. But when insect populations are declining worldwide, with catastrophic effects on the rest of the environment, we need to do practical things to help other ladybirds too.
By Rachael Horwitz
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