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The importance of insects - and the tragedy of their declining numbers

The sheer variety of insects is astonishing, as are their numbers.

About a million species of insect have been described and named, and there are certainly millions more that remain to be discovered and catalogued.

A Banded male demoiselle
A Banded male demoiselle

Insects have six legs as adults, but that is where the similarities end, as there are so many variations on the basic insect body plan. Large numbers of fascinating insects are out and about this month, many of them attracted to gardens, especially those with colourful flowers.

Tragically, insects have declined in abundance by some 75 per cent over the past 50 years, mainly because of a steady loss of their habitats, such as forests, heathland, meadows, and marshes, as well as poisoning by pesticides and pollution of rivers and lakes.

Such reductions in insect numbers have also impacted on populations of insectivorous birds such as cuckoos, swallows, nightingales and spotted flycatchers - numbers of the latter, for example, falling by more than 90 per cent since the late 1960s.

In the UK, the Butterfly Monitoring Scheme has revealed alarming losses over many years, with common species such as peacock and meadow brown falling in abundance by nearly 50 per cent over 40 years, and rarer species such as hairstreaks and fritillaries by nearly 80 per cent since the mid-1970s. There are about 17,500 species of butterfly globally, and we have 59 here in the UK, of which about 20 may turn up in gardens.

Peacock butterfly
Peacock butterfly

While a very small proportion of insect species cause damage to people and their crops, by far the majority are useful and indeed essential for the healthy functioning of natural and semi-natural ecosystems.

Without them, grazed fields would be covered in dung, wild and garden flowers and crops would go unpollinated and pests would thrive, unchecked by their natural predators.

Add to this the fact that countless species of birds, mammals, fish, and amphibians include insects in their diet, and you can see how so much depends upon a healthy and diverse population of insects.

This Nature Note showcases a selection of fine photographs by fellow local naturalist Jonathan Heath, some taken in his own garden in Cambridge.

The banks of the River Cam, where the vegetation is rich, are the habitat of one of our most beautiful damselflies, the banded demoiselle.

The female is green with cream-coloured wings, but the male is bright blue with large blue patches on his wings. Dragonflies are stronger fliers, and some turn up from time to time in gardens as they hunt for smaller flying insects.

Southern male hawker
Southern male hawker

The southern hawker is a large common dragonfly that is often spotted in gardens, gliding alongside hedges and bushes.

Another dragonfly common in southern England, and which seems to be increasing, is the black-tailed skimmer, named for the black tip to the tail of the male.

Black-tailed female skimmer
Black-tailed female skimmer

The female is yellow with black stripes along the abdomen. In the UK, there are 11 species of damselfly and 23 species of dragonfly.

Hoverflies are a fascinating group of insects that, like dragonflies, are very agile in flight.

As their name suggests, they often hover perfectly still in the air, before suddenly darting away. Of the 6,000 species globally, we have around 280.

Wasp hoverfly
Wasp hoverfly

Many hoverflies have boldly striped bodies that mimic those of venomous bees or wasps, thus tricking bird predators which avoid them.

Certain moths have also evolved this strategy, notably the impressive hornet moth that resembles a true hornet sufficiently to deter predation. This is a day-flying moth that belongs to a group known as clearwings.

Hornet moth
Hornet moth
  • Martin Walters is a Cambridge-based writer and naturalist.

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