Origin and importance of insects
Insects feed many birds, bats, hedgehogs, lizards, frogs and fishes. Carrion and dung beetles and fly larvae eat carcasses and dung, and insects that eat plant remains speed decay, cleaning the land – they are natural sanitary animals. Most flowering plants (legumes, melons and gourds) give rich yields when pollinated by insects; bumblebees pollinate alfalfa and clover. There are over 700 pest species: the Asian locust, aphids, codling moth, cotton bollworm, Colorado beetle; in stores the grain beetle, at home the clothes moth, and in buildings termites. Lice, fleas, mosquitoes and bed bugs suck blood and spread diseases (lice – typhus, fleas – plague, mosquitoes – malaria). Biological control uses pests’ natural enemies (ladybirds, lacewings, Trichogramma, insect-eating birds), which reduces the use of toxic chemicals. The ancestors of arthropods are thought to have been many-segmented, worm-like animals of ancient seas. Among the oldest arthropods were the trilobites, which appeared about 520 million years ago and later died out completely; each of their segments carried a pair of similar legs.
Draw a food chain: plant → aphid → ladybird → tit → cat/bird of prey. Safety: spraying toxic chemicals is work for trained adults only; they are kept away from children and food.