Insects and - species outnumber all higher animals by far. Their immense variety reflect adaptation to an extreme range of ecological conditions, even gravely toxic ones. Especially the nearly 60,000 fly species cover about all the globe. Many can fly, which helps getting everywhere, but they also occur on/in soil, water, host plants or animals, cavities etcetera. They often occur in great swarms, as over a billion Monarch butterflies migrating from Canada to a Mexican forest to hibernate. To occupy various positions in ecological systems, usually prey, often predator, sometimes pollinator, and so on.