Hymenoptera are everywhere. If you want to escape them, you will have to go to Antarctica. They are not only ubiquitous, they are highly diverse in lifestyles even though they are specialised in body form. What are they? All the insects that we know commonly as ants, bees, wasps and sawflies.
Hymenoptera translates to clear-wings and these insects have two pairs of transparent wings that are hooked together so they do not operate separately. They do not use one pair for protection like the forewings of the beetles, or one pair as gyroscopes like the second pair of wings in flies. Like the bees and flies though, they go through a complete life cycle that begins as an egg that hatches into a voracious larval eating machine. This larva eventually makes a protective case and pupates into a winged sexually mature adult or an asexual worker if it is a colonial species.
The bees are incredibly important in fertilizing plants in ecosystems around the world, from temperate grasslands to tropical rainforests. This includes over 150 economically important crop species. Bees are highly evolved with complex social systems in which individuals are specialized for different functions. A hive consists of one Queen who lays all the eggs, plus workers who are always female (regardless of what was shown in the Bee Movie!) and a few males who don't work and whose only job is to fly out with new queens and fertilize them before they start new colonies. Bees of course are also a domesticated animal whose product, honey, is economically important.
Ants are the great recyclers and are as important as earthworms in creating and maintaining soils and breaking down dead organic materials. Ants are as social as bees, with similar complex social systems in which colonies have one reproductive female queen and multitudes of workers who are asexual females. Worker and soldier ants do not have wings or fly. Only the queen and her males fly when she is fertilized and then begins a new colony. The males, their duty fulfilled, simply die.
Wasps are distinguished from other hymenopterans by their 'wasp waists', which are constrictions between the thorax and the abdomen. Wasps are important predators and parasites in most ecosystems, where they help to keep other insect species in check. Actually they are neither true parasites nor true predators. True parasites do not usually kill their hosts but larval wasps always kill the host. True predators live on a wide variety of prey species but the adult female wasp looks for just one specific host in which to lay her eggs. Thus wasps are called parasitoids, which are specialists that prey on single insect or spider species, laying their eggs in their chosen victim with the help of their 'stinger', or more accurately, their ovipositor. The eggs hatch inside the victim and the larvae eat their way out.
Hymenopteran fossils first appear in the Triassic Era, some 200 million years ago. The probably evolved from the ancestors of the Mecoptera in the Permian Era about 50 million years earlier. Since then they have evolved in tandem with flowering plants, with which they have a symbiotic relationship: bees collect food from plants and in turn fertilize their hosts. Wasps prey on the other insects that have evolved to eat plant life and ants clean up the remains of both plants and animals.
The last and smallest group of the order Hymenoptera are the mis-named sawflies. They are not flies at all because they do not have halteres but instead two pairs of linked wings, like all other Hymenoptera. They are the most primitive of the group and get their name from a saw-like ovipositor that is used to insert eggs into plant tissues. The larvae are major pests of crop plants because they hatch in large numbers and are voracious when they do.
Many people are afraid of bees and wasps and rightly so. Their stings can be painful and even deadly. However they are also very important components of most ecosystems. They perform many important functions including predation on herbivorous insects, fertilizing many flowering plants, producing honey and creating and maintaining soils. Life would be a lot less diverse, colourful and interesting without them.
Reference: The Encyclopaedia of Insects, 1986, edited by C. O'Toole, George Allen & Unwin