Insects disappearing

[Lisbeth]

No bugs on your windscreen is bad news for swallows

By Don Pinnock• 13 June 2021


Image: TheOtherKev / Pixabay

If you want to gauge the state of the planet, you don’t have to be a scientist, you just have to look for what’s missing around you.

We are essentially creatures of two dimensions and only slightly of the third: up. Above us is the kingdom of air, clouds, flying insects and birds.

Of all these creatures, one among them is its most permanent resident: the swallow. From the moment it flies out of the maternal nest it remains mostly airborne for about two years, seldom landing, always flying and sleeping on the wing.

It is well named. In relation to its size, it has an enormous mouth surrounded by an almost useless little beak. There’s a reason for this. It needs its beak only to roll mudballs to make a nest when it eventually comes down to earth to breed (it’s impossible to incubate eggs in mid-air) and to offer tidbits to chicks. For the rest it catches insects on the wing by diving at them with a gaping maw.


Bird in full flight. Image: Pixabay

While, as Shakespeare put it, one swallow does not a summer make, a bunch of them lets you know it’s on the way. And so it has been since humans first noticed this at the dawn of our species. Where they went in winter was not known until relatively recently. It was once speculated that they wintered underground.

But in many parts of the world these days, one swallow – or maybe two or three – is all you get. They’re in deep trouble. The reason has to do with the Silence of the Bugs.

Let me ask you a question: when did you last wipe a bug splat off your windscreen? Or dig butterflies out of your radiator? I bet not often – and that’s extremely worrying.


Regal butterflies on an orange flower. Image: Joshua Torres / Unsplash


Two peacock butterflies perched on yellow flowers. Image: Pexels

The reason is that we’re running out of them and very few scientists are marking their passing. Biology these days happens in the DNA lab. As a result, there are fewer and fewer field biologists to raise red flags about insect decline. But if swallows could, they would.

What’s happening is in fact an insect Armageddon, particularly in developed countries.


Image: Bankim Desai / Unsplash


Image: liggraphy / Pixabay


Scarab beetle. Image: USGSBIML Team

A study over 27 years in 63 protected areas in Germany found an alarming 82% decline in flying insects and a 76% decline in all insects. Africa’s not so bad, but the bug-on-your-windscreen test suggests we’re still in trouble.

In a detailed study over 20 years, Danish etymologist Anders Møller found the abundance of flying insects killed on windscreens decreased by more than 80%. Lower abundance of insect windscreen splats correlated with lower numbers of three species of aerially insectivorous birds, particularly swallows, and the rate at which they fed their nestlings.


Image: TheOtherKev / Pixabay


Blue beetle. Image: James Wainscoat / Unsplash


Image: Pixabay

Let’s look at the wider implications beyond the crisis for swallows. We live in an invertebrate world. Of all known species, fewer than 5% have backbones. The other 70% are insects. They’ve been on Earth far longer than humans. In many ways, they created the world we live in.

It’s easy to care about iconic mammals. We could soon be living on a planet without rhinos, elephants, mountain gorillas, lions and tigers. For sure it would be a sad place.


Image: liggraphy / Pixabay


Image: image4you / Pixabay


Image: James Wainscoat / Unsplash


Jumping spider. Image: Max Pixel

But the possibility of invertebrate extinctions is to confront a different order of loss. So much will disappear before we even knew it existed. Harvard entomologist EO Wilson estimates that without insects, humanity would last just a few months. The result would be a food-chain cascade to the bottom.

Most amphibians, reptiles, birds and mammals would go next. Flowering plants would be history. The planet would become a compost heap, covered carcasses and dead trees that couldn’t rot. Fungi would have their day then they too would die off.

The Earth would revert to what it was like 440 million years ago, when life was just beginning to colonise the soil – a silent place of mosses and liverworts waiting for the first invertebrate brave enough to try its luck on land.

So we need to pray for more insect smears on our windscreens, moths round our candles and butterflies in our radiators. Let’s nurture the caterpillars that become butterflies, leave the grasshoppers on our lawns, be happy about crickets in our gardens and stop hitting them with insecticide.

For a start, maybe make this a Be Kind to Bugs Month. We need them much more than they need us. And if swallows are to be around to herald spring, they need them too. DM/ML

[Richprins]

[Lisbeth]

The insect apocalypse: ‘Our world will grind to a halt without them’

Dave Goulson
Sun 25 Jul 2021 10.00 BST

Insects have declined by 75% in the past 50 years – and the consequences may soon be catastrophic. Biologist Dave Goulson reveals the vital services they perform

Click on the title to read the whole study.

[Richprins]

Well, they have only notably declined here in the last 5 years?

Still a disaster.

[Klipspringer]

Wherever there is long term data (such as the famous German study over 20 years) there is a massive decline.
In South Africa there is just no data available.

It's all about habitat destruction and the environmental foodprint we leave as consumers.

[Lisbeth]

Insects are vanishing worldwide – now it’s making it harder to grow food

: February 15, 2023 | Stuart Reynolds
Emeritus Professor of Biology, University of Bath

Over the past 20 years a steady trickle of scientific papers has reported that there are fewer insects than there used to be. Both the combined weight (what scientists call biomass) and diversity of insect species have declined. Some studies were based on sightings by amateur entomologists, while others involved scientists counting the number of bugs splattered on car windshields. Some collected flying insects in traps annually for years and weighed them.

In the past six years, this trickle has become a flood, with more and more sophisticated studies confirming that although not all insect species are declining, many are in serious trouble. A 2020 compilation of 166 studies estimated that insect populations were on average declining globally at a rate of 0.9% per year. But the declines are uneven. Even within the same environments, populations of some insect species have waned, while others have remained stable and still some others increased. The reasons for these differences between insects are unknown, though evidently some are more resilient than others.

Until recently, much of the evidence has been drawn from protected areas in Europe and to a lesser extent North America. So what is the picture like elsewhere? A new study offers fresh data on the seasonal migrations of insects in east Asia. These insects, many of them pest species, fly north in spring every year to take advantage of the new growing season, and fly south in autumn to escape the cold.


A sky filled with monarch butterflies.
Insects can travel thousands of miles in seasonal migrations. Javarman/Shutterstock

A progressive fall in the enormous numbers of these migrants indicates that insect declines are indeed a global problem.

Millions of migrating insects

Between 2003 and 2020, scientists from the Chinese Academy of Agricultural Sciences in Beijing caught almost 3 million migrating insects from high-altitude searchlight traps on Beihuang Island off the coast of northeast China. A further 9 million insects were detected from radar records. In all, 98 species were identified and counted, most of which were either plant-eating crop pests or insects that are their natural enemies – predators and parasites. Over the whole 18-year period, the yearly tally of all identified insects fell by 7.6%, a steady downward trend of 0.4% a year.

Insect declines clearly are occurring on a large scale in Asia, just as they have been in Europe and North America. It seems reasonable to assume that the causes are the same. Although we don’t know for certain what those causes are, it seems likely that they operate all over the world.

The study also showed that pest insects such as the black cutworm moth, whose caterpillars attack a wide variety of vegetable crops, are as strongly affected by the global decline of insects as non-pest species such as bees and butterflies that were the subjects of most of the previous European and American studies.

We are so used to considering insects as pests that it is tempting to think that, in a world with fewer of them, agriculture might prosper as never before. This new study reveals why that is not the case. The researchers used detailed entomological records from the past to construct a complex food web showing how each of the insect pest species caught in the searchlight traps can be eaten by several kinds of insect predators and parasites, often termed “natural enemies”. As an example, black cutworm caterpillars are eaten by green lacewings, among others.


Green lacewings eat crop pests – but there are fewer of them in farm fields. Cornel Constantin/Shutterstock

The researchers compared how fast 124 pests had declined alongside each of their natural enemies. Over the 18-year study, the abundance of natural enemy species fell at a rate of 0.65% a year, while the plant-eating prey did not decrease in number at all, on average. This suggests that beneficial natural enemy species are more likely to decline than the pests that they feed on. As a result, farmers must either tolerate lower crop yields or use even more chemical insecticides to control pests, leading to still worse declines.

Although it is tempting to point a finger at pesticides, bright streetlights or climate change, insect declines almost certainly have multiple causes that overlap.

The most frequently named suspect is agricultural intensification. This term covers a multitude of sins. Farm mechanisation, the eradication of hedges, crop monocultures, the increased use of chemical fertilisers and regular applications of pesticides are all intended to produce fields without weeds, pests or diseases. Only a reduced range of wild plants and animals can survive in the narrow field margins and neighbouring roadside verges that remain. Another way of putting it is that farmers have made fields unwelcoming to most insects.

Intensification is designed to ensure that as much as possible of the farm ecosystem’s energy flow is diverted into growing crops and livestock for human consumption. It has been estimated that 24% of all plant growth annually is now appropriated by humans, and this rises to a staggering 69% on cropland. These figures roughly doubled over the 20th century. It’s no wonder that insects don’t do well in landscapes such as these, and farmland occupies almost 40% of the land.

Why you’ll miss bugs

Insects are by far the most numerous of all animals on Earth. The estimated global total of new insect material that grows each year is an astonishing 1,500 million tonnes. Most of this is immediately consumed by an upward food chain of predators and parasites, so that the towering superstructure of all the Earth’s animal diversity is built on a foundation of insects and their arthropod relatives.

If insects decline, then other wild animals must inevitably decline too. There is already evidence that this is happening. In North America, insect-eating bird species experienced an average decline in population size of almost 10 million over the past 50 years, while those for which insects are not essential prey did not decline at all. In Europe, parallel declines of insectivorous swallows, house martins and swifts have all been linked to insect declines.

While it’s true that a few insects are a menace to humans (disease-carrying mosquitoes come to mind), the vast majority of insects are friendly: they pollinate crops, provide natural pest control, recycle nutrients and form soil by aiding the decomposition of dead animals and plants. All these processes will slow down if insects become scarce. The economic value of these services is incalculable – agriculture could not continue for long without them.

Our insect friends are being crowded out. Somehow, we must find ways to make more room for them.

[Richprins]

We used to have hundreds of big green grasshoppers around the lights at night here about 10 years ago. They have quickly become fewer over the years and this season none at all...

[Lisbeth]

We ar getting closer and closer to a natural disaster