A remarkable variety of insects live in this planet. More species of insects exist than all other animal species together. Insects have survived on earth for more than 300 million years, and may possess the ability to survive for millions more.
Insects can be found almost everywhere—on the highest mountains and on the bottom of rushing streams, in the cold South Pole and in bubbling hot springs. They dig through the ground, jump and sing in the trees, and run and dance in the air. They come in many different colors and various shapes. Insects are extremely useful to humans, pollinating (授粉) our crops as well as flowers in meadows, forests, deserts and other areas. But ticks and some insects, such as mosquitoes and fleas, can transmit disease.
There are many reasons why insects are so successful at surviving. Their amazing ability to adapt permits them to live in extreme ranges of temperatures and environments. The one place they have not yet been found to any major extent is in the open oceans. Insects can survive on a wide range of natural and artificial foods--paint, pepper, glue, books, grain, cotton, other insects, plants and animals. Because they are small, they can hide in tiny spaces.
A strong, hard but flexible shell covers their soft organs and is resistant to chemicals, water and physical impact. Their wings give them the option of flying away from erous situations or toward food or mates. Also, insects have an enormous reproductive capacity: An African ant queen can lay as many as 43,000 eggs a day.
Another reason for their success is the strategy of protective color. An insect may be right before our eyes, but nearly invisible because it is cleverly disguised like a green leaf, lump of brown soil, gray lichen (青岩), a seed or some other natural object. Some insects use bright, bold colors to send warning signals that they taste bad, sting or are poison. Others have wing patterns that look like the eyes of a huge predator, confusing their enemies. Some insects also imitate bitter-tasting insects; hungry enemies are fooled into avoiding them. The passage is mainly about ______.