Where have all our insects gone?
The European oil
beetle, one of many insect species under threat in the UK. Photograph: Alfred Schauhuber/imageBROKER/REX/Shutterstock
There is a crisis in the countryside – and a massive decline
in insect numbers could have significant consequences for the environment
by Robin McKie, Observer science editor
Sun 17 Jun 2018 09.00 BST
When Simon Leather was a student in the 1970s, he took a
summer job as a postman and delivered mail to the villages of Kirk Hammerton
and Green Hammerton in North Yorkshire. He recalls his early morning walks
through its lanes, past the porches of houses on his round. At virtually every
home, he saw the same picture: windows plastered with tiger moths that had been
attracted by lights the previous night and were still clinging to the glass.
“It was quite a sight,” says Leather, who is now a professor of entomology at
Harper Adams University in Shropshire.
But it is not a vision that he has experienced in recent
years. Those tiger moths have almost disappeared. “You hardly see any, although
there used to be thousands in summer and that was just a couple of villages.”
It is an intriguing story and it is likely to be repeated
over the next few weeks. The start of summer is the time of year when the
nation’s insects should make their presence known by coating countryside
windows with their fluttering presence, and splattering themselves on car
windscreens. But they are spectacularly failing to do so. Instead they are
making themselves newsworthy through their absence. Britain’s insects, it
seems, are disappearing.
This point was underlined last week when tweets from the
naturalist and TV presenter Chris Packham went viral after he commented on the
absence of insects during a weekend at his home in the New Forest. Packham said
he had not seen a single butterfly in his garden, and added that he sleeps with
his windows open but rarely finds craneflies or moths in his room in the
morning. By contrast, they were commonplace when he was a boy. “Our generation
is presiding over an ecological apocalypse and we’ve somehow or other
normalised it,” he later said.
Certainly, the statistics are grim. Native ladybird
populations are crashing; three quarters of butterfly species – such as the
painted lady and the Glanville fritillary – have dropped significantly in
numbers; while bees, of which there are more than 250 species in the UK, are
also suffering major plunges in populations, with great yellow bumblebees,
solitary potter flower bees and other species declining steeply in recent
years. Other threatened insects include the New Forest cicada, the tansy beetle
and the oil beetle.
As for moths, some of the most beautiful visitors to our
homes and gardens, the picture is particularly alarming. Apart from the tiger
moth, which was once widespread in the UK, the V-moth (Marcaria wauaria)
recorded a 99% fall in numbers between 1968 and 2007 and is now threatened with
extinction, a fate that has already befallen the orange upperwing, the bordered
gothic and the Brighton wainscot in recent years.
An insect Armageddon is under way, say many entomologists,
the result of a multiple whammy of environmental impacts: pollution, habitat
changes, overuse of pesticides, and global warming. And it is a decline that
could have crucial consequences. Our creepy crawlies may have unsettling looks
but they lie at the foot of a wildlife food chain that makes them vitally
important to the makeup and nature of the countryside. They are “the little
things that run the world” according to the distinguished Harvard biologist
Edward O Wilson, who once observed: “If all humankind were to disappear, the
world would regenerate back to the rich state of equilibrium that existed
10,000 years ago. If insects were to vanish, the environment would collapse
into chaos.”
The best illustration of the ecological importance of
insects is provided by our birdlife. Without insects, hundred of species face
starvation and some ornithologists believe this lack of food is already causing
serious declines in bird numbers, a point stressed by the naturalist and
wildlife author Michael McCarthy. “Britain’s farmland birds have more than
halved in number since 1970,” he points out. “Some declines have been
catastrophic: the spotted flycatcher, a specialist predator of aerial insects,
has both declined by more than 95%, while the red-backed shrike, which feeds on
big beetles, became extinct in Britain in the 1990s.”
Further confirmation of the link between insect and bird
numbers was provided last week with the publication of a study by Aberdeen University
researchers which showed that the plunge in numbers of cuckoos in some areas of
England was closely linked to declines in tiger moth caterpillars on which
cuckoos feed.
“There is now a lot of correlational evidence to show that
when certain insects do badly, very often the birds that feed on them get into
trouble as well,” said David Gibbon, of the RSPB.
However, insects also play invaluable roles in other parts
of the environment – for example as pollinators of our orchards and fruit
fields. And again, scientists are worried. “People think that it is just bees
that pollinate orchards, but there are huge numbers of flies that also
pollinate – and they are all also threatened,” said Leather.
In addition, flies, beetles and wasps are predators and
decomposers who control pests and who generally clean up the countryside. “Just
think of the work of the dung beetle,” added Leather. “If they go, the land
would be covered with the excrement of cows, sheep and other animals.
But perhaps the most alarming indication of the ecological
apocalypse we face was provided a few months ago by researchers who published a
startling paper in the journal Plos One. Their work was based on the efforts of
dozens of amateur entomologists in Germany who began employing strictly
standardised ways of collecting insects in 1989. They used special tents called
malaise traps to capture thousands of samples of insects in flight over dozens
of different nature reserves.
Then the weight of the insects caught in each sample was
measured and analysed – revealing a remarkable pattern. The annual average
weight of insects found in the traps fell by 76% over the 27-year period of
their research. Most alarming, however, was the discovery that the decrease was
even higher – 82% – in summer, a time when insect numbers should reach their
peak.
Such figures give strong numerical support to the veracity
of anecdotes about splattered car windscreens and moth-plastered patio windows
becoming a thing of the past. Equally stark is the fact that although
meteorological patterns fluctuated to some degree during the years of the
study, it was clear that weather was not the cause of the declines.
But perhaps the most alarming aspect of the research was the
realisation that these grim drops in insect numbers were occurring in nature
reserves – in other words, in areas where the landscape was highly protected
and should be the most friendly of habitats for insects. Conditions elsewhere
were likely to be a lot worse, the scientists warned.
“Insects make up about two-thirds of all life on Earth [but]
there has been some kind of horrific decline,” Professor Dave Goulson of Sussex
University, said at the time. “We appear to be making vast tracts of land
inhospitable to most forms of life, and are currently on course for ecological
armageddon. If we lose the insects, then everything is going to collapse.”
The fact that insect biomass has been declining at a steady
rate for almost three decades strongly suggests some profound influences must
be at work. Most entomologists believe habitat change lies at the heart of the
problem. “There have been massive alterations to the way we use the land and it
is hard not to believe these are closely involved in what we are seeing,” said
Leather.
As he points out, intensively farmed wheat and cornfields
support virtually no insect life, and this means that as intensive agriculture
spreads there are fewer and fewer islands of natural habitat left to support
them.
And then there is the issue of urban spread. Housing schemes
continue to encroach on our woods and heaths so that streets and buildings
generate light pollution that leads nocturnal insects astray and interrupts
their mating. “That is the reason we see most changes to insect life in
south-east England, for that is where we see the greatest spread of cities and
towns,” said Leather.
In addition to habitat changes, there are the dangers posed
by pesticides, in particular neonicotinoid pesticides, which have already been
blamed for recent crashes in bee populations. These chemicals are water soluble
and so leach out of fields after they are applied to crops.
According to research quoted in the journal Science last
year, these pesticides have since been found in high concentrations in nectar
and pollen in wildflowers near treated fields. Though still not at levels
sufficiently high to kill insects directly, they do affect their abilities to
navigate and communicate.
In the face of this mixture of ecological woes, it is
perhaps not surprising that insects in Britain are faring so badly. Whether or
not they face an ecological apocalypse is a different matter, for not every
expert shares a sense of doom. Professor Helen Roy of the Centre for Ecology
and Hydrology, for example, sees cause for hope. She told the Observer that
there were too many success stories – tales of insects that were recovering in
numbers and thriving – to feel a sense of despair. “Obviously, many species are
suffering, but I am an optimist and I just don’t think it is right to call this
an apocalypse,” she said.
Roy pointed to explosions in the number of ladybirds and
painted lady butterflies that have occurred in the past as evidence. “There are
huge variations in numbers of a particular insect species in a year and huge
variation in the places you see them.” She also pointed to one study of
pollinators that showed while 32% became less widespread between 1980 and 2014,
16% became more widespread. “It is not all doom and gloom,” Roy added.
This view was supported by David Gibbons of the RSPB who
agreed that not every investigation about insect numbers revealed a tale of
irrevocable decline – though he added that he still believed the overall
picture was worrying. “It is hard not to see a link between some of the bird
number declines and drops in insect populations we are experiencing. There are
very close correlations in many cases. But proving there is a causative link –
in establishing the one effect is leading to the other – is much more
difficult.”
We appear to be
making tracts of land inhospitable to most forms of life. If we lose insects,
it all collapses
An illustration of the problem is provided by one of the few
cases where a causative link between insect loss and bird-number declines has
been established: the grey partridge, Gibbons said. “During the 70s and 80s,
pesticides were killing off plants on which sawflies and other insects fed.
Grey partridge chicks feed on these insects and so this process led to a
decline in their numbers – and that has since become dramatic.” In fact, the
grey partridge’s drop in numbers has brought its population to less than 5% of
its figure last century.
The crucial point is that researchers were able to show that
these twin declines were connnected by manipulating herbicide levels in places
where chicks were being reared. When herbicide levels went up, insect levels
went down and so did bird numbers. “That manipulation provided the causative
link,” said Gibbons. “It was possible to change insect numbers and so see the
impact. However, such research is difficult to carry out and is very rare.”
And of course, threats to our birdlife are only one aspect
of the dangers posed by losses of insects in the UK. As entomologists point
out, they also keep our soil fertile, degrade waste, pollinate our orchards and
control pests such as the aphid.
“We cannot afford to lose them and that’s what makes this
issue so urgent and so important,” Leather concluded. “That’s worth keeping in
mind as the summer evenings begin – and we see hardly any insects.”
Ladybirds
Many of Britain’s native species of ladybirds are suffering
serious declines in numbers, thanks to the arrival of the harlequin ladybird.
It has been declared the UK’s fastest invading species, after reaching almost
every corner of the country in just a decade. It preys on native ladybirds and
is believed to have caused the decline of at least seven species, including the
popular two-spot ladybird, which – when last assessed in 2012 – had slumped by
44% in numbers.
Moths
More than 2,500 moth species have been recorded in Great
Britain, of which around 900 are called larger moths. In the report The State
of Britain’s Larger Moths 2013, it was revealed that larger moths had declined
by 28% between 1968 and 2007. This was most noticeable in southern Britain
where there was a 40% decline. By contrast, numbers showed no significant
change in northern Britain, where disappearing species are balanced by moths
spreading north because of climate change.
Bees
Seventy of the 100 crop species that provide 90% of food
worldwide are pollinated by bees. In the UK, there are more than 250 species of
bee: 25 species of bumble bee, 224 species of solitary bee and one honey bee
species. According to a government report in 2014, figures there has been an
overall decline in wild and honey bees over the past 50 years. The figures also
revealed evidence that there has been parallel declines in the plants that rely
on them for pollination.
Butterflies
The State of the UK’s Butterflies report – produced in 2015
by Butterfly Conservation – provided further evidence of “the serious,
long-term and ongoing decline of UK butterflies”. Overall, 76% of the UK’s
resident and regular migrant butterfly species had declined in either abundance
or occurrence (or both) over the past four decades, it was found. “This is of
great concern not just for butterflies but for other wildlife species and the
overall state of the environment,” the report noted.
Beetles
These insects eat large volumes of slugs and aphids and
large numbers of weed seeds, thus helping to stop fields being overrun by
unwanted plants and pests. However, a study, published in the Journal of
Applied Ecology in 2012 - which looked at 68 beetle species at 11 locations
around the British Isles over 15 years - found that three-quarters of those
examined had declined in number over the periodOf these, half had fallen at
rate equivalent to 30% per decade.
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