Crede Holgate, of Balclutha Primary School, asks :-

Why do we have insects in our world?

John Marris, an entomologist who is curator of the Entomology Research Museum at Lincoln University, responded.

The simple answer to this question is that we have insects because they have successfully adapted to our world through hundreds of millions of years of evolution.

They are some of the most common, diverse and widespread organisms on the planet. Take a quick look at the numbers – there are around 5,500 sorts of mammals on the planet, while birds do a bit better with around 10,000 species. Plants come in at a respectable 400,000 species or thereabouts, while fungi (1.5 million) and others such as bacteria and viruses (2.6 million) are much more diverse. The insects come out comfortably on top though with a mind-boggling 5 million species.That might even be a conservative estimate as others have been much higher. Insects are so diverse that you could argue that we live in the age of the insects and have been doing so for many millions of years.

Insects have been winners in the battle for the ‘survival of the fittest’. They have survived and flourished, in competition with other organisms, through more than 400 million years of evolution. So, what is it about insects that has made them so successful? We can’t be sure for certain without having a crystal ball to gaze back into the evolutionary past, but we can make some pretty good guesses. One factor that is probably very important is the small size of insects, with some fully grown species as little as 0.3 mm in length. Being small means that many opportunities exist to make a living. An example is a single tree that may support one or a few larger creatures, but provide a multitude of habitats for a wide range of insects. These may include root feeders living underground to foliage feeders in the canopy, some that rely on flowers or seeds for food and others still that prey on or parasitize occupants of the tree. The small size of insects has allowed them to diversify hugely into all imaginable ecological niches.

Many other factors may be important in the success of insects. The early emergence of insects in the history of life may have given them a critical head start over the competition, from which they never looked back. The rapid reproduction rate of insects helps them to adapt quickly to changing environments. For example, insects evolved together with the flowering plants as they became dominant features of the land, which opened up new opportunities for insects to exploit. Insects were the first creatures to fly, millions of years before birds, bats or even the ancient dinosaur-like pterosaurs took to the skies. This gave insects an early advantage in adapting to the new habitats and environments that flying presented.

These are just some of the possible explanations for the existence and success of insects. What can be certain about is that insects are a hugely successful group and have been for a very long time.