Ladybirds are everywhere at the moment. They were landing in my hair last weekend, and there are reports of them invading classrooms, clustering on sunny walks and divebombing picnic tables. They have obviously had a very good year. Early warmth, mild moisture and a hot summer meant plenty of aphids (greenflies) for them and their larvae to eat. Several rapid generations later their populations exploded, but then came the crash. They’d eaten all their aphid prey, and faced with starvation they took to the air in search of pastures new, or at least new herds of greenfly.
Normally you might not spot the odd ladybird flying from one bush to another, but now there are hundreds of them, sometimes many thousands. I well remember the great ladybird swarm of 1976, when the streets of Brighton were inundated. The skies were, if not quite darkened, then certainly polka-dotted with them wherever you looked up. They speckled cars and buses, and the pavements became slippery with their crushed bodies as they were trodden underfoot. A few days later a red tide left a scarlet strandline a metre wide along the beaches, and estimates were easily bandied about — of the tens or hundreds of millions of ladybirds drowned in the sea.
That was the first time I was bitten by a ladybird too. It happened again this year.
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Most beetles have short biting jaws, and although it was just a playful nip on the bare forearm, it was wholly unexpected. No, it was not trying to eat me. I was being tested. Though it had landed on my bare skin, rather than the leaf of a bush, the instinctive response was the same — take a taste check. When a ladybird lands on a plant it takes a small bite. It cannot eat the plant, but it can taste whether that plant is under attack from greenflies.
As aphids feed by sucking out the sap, the plant responds with defence chemicals called kairomones. These chemical compounds are alarm triggers which are recognised by any ladybirds coming to the plant’s rescue. If the test is positive the ladybird sets off on foot in search of the plant’s aggressors and starts tucking in. If it’s negative, as it was when it bit me, it flies off to try somewhere else.
There is another ecological imperative in the mix. It may well be a lovely, warm day, but it’s October for goodness’ sake, and the weather can flip in a trice. All ladybirds overwinter as adults, and if they are to make it through to next year, when mating and egg-laying takes place, they need to get under cover and find hibernation quarters very soon. That’s what they’re doing crawling over the brickwork of the walls, scrabbling around window sills and masonry ledges, or trying to come indoors to explore the covings and the back of the curtains. Soon they will be tucked into huddles of half a dozen to many hundreds.
Since 2004 the harlequin ladybird, Harmonia axyridis, has become more common than the seven-spot variety
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As they snuggle down they release an aggregation pheromone, a chemical scent that means they are safe and dry, and which attracts others to the security of whichever corner they have settled in. Drifts of many thousands are not uncommon. The chemical scent lingers and ladybirds will huddle in the same corners year on year. These are not the same individuals returning to a familiar home base, but the descendants (often by two or three generations) of those ladybirds that rested there last year. Others will be there again next year too.
Back in 1976 it was the familiar seven-spot, Coccinella septempunctata, that made national headlines. But since 2004 it is the harlequin ladybird, Harmonia axyridis, which has become the usual suspect. Originally a native of central and eastern Asia, this large and voracious ladybird has been commercially reared and deliberately released as a biocontrol agent against problem aphid attacks on garden and farm crops around the world.
The swarm of 1976, as suffered in Burnham-on-Sea
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It is now widespread in the rest of Asia, north Africa, Europe and the Americas. Soon gaining a reputation for eating the larvae of other ladybird species and other native insects, as well as the target greenfly, it has been tainted by stories which feed the narrative that it is an invasive alien. This is an anthropomorphism too far. As usual it is us humans that have interfered with the balance of nature: the ladybirds are just trying to find a place to rest up for the winter.
Richard Jones is an entomologist and naturalist, and a fellow of the Royal Entomological Society. He has written several books including Beetles, in the HarperCollins New Naturalist Library series.
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