At first I thought they were falling leaves, blown by the breeze. They were very beautiful, as is always the case with butterflies, but they are just insects, of course.

So are ants, so are cockroaches.

There are 1,017,018 species of insects in the world with some experts estimating that there may be more than 10 million species in all.

Most insects are beetles: about 300,000 have been identified to date.

Butterflies and moths are the second largest group, with 165,000 described species and an estimated additional 100,000 yet to be described.

Scientists estimate 10% of the animal biomass of the world is composed of ants, and another 10% of termites. ‘Social insects’ could possibly make up 20% of the total animal biomass on this planet.

There isn’t anywhere you can go on dry land where you won’t find insects. Even in the Arctic and Antarctica insects have evolved to live successfully during the warmer months. Meanwhile, in all other regions of the world they are in the soil beneath our feet, in the air above our heads, on and in the plants and animals around us – but hopefully, in these hygienic times, not on or in ourselves.

It is estimated that there are approximately 10 quintillion –10,000,000,000,000,000,000 – individual insects on the planet. The estimate was, presumably, made on the basis of counting insects in transects of pre-defined size in diverse environments.

It is estimated that on average there are more than a million insects living on every single acre on earth.

Together, they eat more than all other creatures combined; this includes dead wood, dead and living plant stems and leaves, and dead birds and animals. They are essential in cleansing of the land and pollinating the crops upon which we rely.

They, in turn, provide a major food source for a wide range of animals and birds which, also, are essential to the health of our environment.

However, insects can be hugely destructive.

Desert locusts have plagued agriculture in Africa and Asia for millennia. A single swarm can be composed of billions, with up to 80 million per square kilometre spread out over a thousand square kilometres.

Each individual can devour its own weight – 2g – in fresh food in 24 hours. A ton of locusts, which is a tiny part of the average swarm, eats the same amount of food in a single day as 10 elephants, 25 camels or 2,500 people.

Insects come in amazing number of sizes, shapes and behaviour, but they all have characteristics in common: three body parts – a head, thorax and abdomen – six jointed legs and two antennae.

The antennae serve to sense the world around them from inside their skeleton which, in their case, is on the outside of the body (an exoskeleton), like a carapace protecting it.

Flexible joints between the skeletal plates allow them to move. All insect species lay eggs and most go through four stages of metamorphosis: egg, larva or nymph, pupa, and adult. Most, but not all, have wings at some point in their lifetime.

Entomologists believe that insects are successful because of their protective shell, small size and ability to fly, features that help them escape from enemies and travel to new environments.

Insects have been around for 390 million years and prototype cockroaches for 300 million.

By comparison, we’re johnny-come-latelys – our human ancestors evolved in Africa only 190,000 years ago and set off to colonise the world 30,000 years later. It is said that in the event of our blowing up the planet, the life most likely to survive (if any) is cockroaches.

Cockroaches have survived freezing, irradiation, microwaving and prolonged submersion. They might even survive a nuclear holocaust.

Meanwhile, to return to the diaphanous creatures floating with the autumn leaves in the sunlit garden, their ancestors, closely resembling present-day species, can be found as fossils dating from 40 million years ago.

So, we may well imagine that on an autumn day a mere 100,000 years ago, some hairy hominoid sitting under a tree mistook windblown butterflies for windblown leaves. However, being Homo sapiens sapiens, he would have learned from his mistake.

Sapience was the inclination, and sapient was the man. Let us hope wisdom and the learning curve prevails, and cockroaches do not inherit the earth.