You may have never seen a mecopteran, such as a scorpionfly or a hangingfly, because the adults are so secretive. They hide out in dark, shaded woodlands. They don't fly much, spending most of their time sitting on leaves. Mating tends to occur at night. Mecopterans actually live all over the world, even in polar habitats. They prefer moist, shady conditions, like what you find in dense forests. Females lay eggs under damp leaves or soil on the forest floor, and the larvae develop in the dark hiding places. In polar areas, larvae may develop in clumps of moss surrounded by snow. Mecopterans are closely related to fleas and flies. But, mecopterans are larger, often with long, clear wings patterned with dark veins. Their heads are long too, narrowing down to where their mouthparts (mandibles) attach. Despite the sinister appearance created by their long, thin faces, they do not bite or sting.

Insects are by far the most diverse and abundant group of organisms on Earth. More than one million insect species have been identified, and estimates of how many species exist range into the tens of millions. Insects got their start way back, in the Paleozoic (about 500 million years ago) and have evolved in tandem with flowers (coevolution). Insects have become specialized on particular flowers, leading to complex sets of adaptations that couple them in a feeding and pollination relationship (a mutualism). Specialization allows for many types of insects to live in the same habitat, accommodating their exceptional biodiversity. In a backyard in the temperate zone, one might find several thousand species of insects. Specialization can occur within one plant species as well, with different insects using different parts of the plant. In just one species of tropical tree, Dr. Terry Erwin of Smithsonian's National Museum of Natural History found about a thousand species of beetles.