Many people tend to overlook insects due to the fact that at first glance they can often appear to be nothing more than a nuisance to be squashed underfoot. However in reality, insects are essential for the survival of all other forms of life on the planet, and have also affected mankind in particular in many diverse ways. From transferring deadly diseases that have decimated populations to being an essential source of food for many groups of people, insects are undeniably important.
Probably the most important natural process that insects are known for is the pollination of many different species of plants, which is a mutually beneficial process that has evolved over millions of years. This process simply couldn't function without insects, particularly bees, butterflies and the like, who each pollinate thousands of flowers in their short lifetimes. Even with the intervention of scientific methods of pollination, mankind would not be able to keep up with the work done by these pollen and nectar feeders. So as a result many of the different colors, patterns and shapes that we see in nature today are a direct result of insects.
One of the most important things that insects have been used for is experimentation for modern science using live subjects. Due to the fact that certain chemicals can't realistically be used on either humans or animals for cruelty reasons, insects often make good test subjects. Also the fact that they are more simplistic than animals means that scientists can better understand the effects of experiments on insects over longer periods. Due to most insects short lifespans experiments can also be done over the course of multiple generations much faster than it could be even with lab mice.
Similarly, many insects produce byproducts that are useful to humans in some way, bees for example make honey. Broadening the criteria to include all invertebrates certain species of spider make silk strong enough to be used for netting. Many species also produce toxins and venom which can be harnessed and adapted for a variety of scientific applications.
One of the most important jobs that insects do is to eat all the debris and rubbish that would otherwise quickly build up and bury civilization. Insects eat everything from rotting leaves and wood, to the dead bodies of animals and tiny particles that float around in the wind. Without them this debris would eventually build to such an extent that it would literally bury people in their own waste. For example woodlice and millipedes feed on rotting plant material and wood, similarly to ants who eat everything from other insects to the food waste that we dump in landfill sites every day.
Insects have also been important in the development of many other kinds of inventions, modes of transport, works of art, and even robots used by NASA. Because of the innovative and diverse ways that insects both move and hunt, many of their characteristics have been successfully used by humans for millennium in developing all manner of different applications. For example moon landing robots are often based on the movements of insects such as ants. Also they are being developed to mimic the actions of grasshoppers in order to allow them to travel great distances in weak atmospheres.
Several of the lower levels of any food chain based is always insects, both predators and prey, and all levels on any food chain depend on the other levels in order to correctly function. The simplest food chain is probably that birds feed on worms, which in turn take nutrients out of the soil. The birds that feed on them are then in turn eaten by species such as foxes or larger birds. Without any one of the layers in these food chains, the other layers would not work either, and eventually the entire food chain becomes extinct.
Insects are also carriers of a variety of diseases, such as malaria from mosquitoes or smallpox from fleas. Although both devastating in their own ways, the changes that they have brought about has been huge on the development of the world as we know it today. The plague for example essentially ended the feudal system in medieval Europe, and ushered in the age of exploration and colonization. Similarly the fact that such a large percentage of people were killed means that the gene pools were affected and changed forever, all due to one of the smallest of insects that most people now see as nothing more than a pest to be poisoned.
Despite the technological and scientific advances of the last few hundred years, in the opinions of most experts there is little debate as to which species will be left after mankind dies out. Those species are the insects, cockroaches and scorpions for example, which are both known to be able to resist high levels of radiation. In the event of a nuclear war, or astral body hitting the earth and destroying civilization and society, undoubtedly the smallest of species such as the insects would be the survivors.
From the earliest fossil records right through until today, insects have survived and prospered where every other type of creature has fallen. There have been millions of species that have lived on the planet earth over the billions of years that life has been present. However only the insects and the bacteria have proven to be both adaptable and tough enough to have survived all the various changes that the planet has gone through.