Order

CHAPTER

phylum class subclass • order monotypic order suborder family

PHYSICAL CHARACTERISTICS

Adult hymenopterans (HAI-men-OP-teh-runs) range in size from 0.006 to 4.72 inches (0.15 to 120 millimeters) in length. The bodies of many wasps are slender, while those of bees are robust. They often have large compound eyes, each with many lenses. Some also have simple eyes, or eyes with one lens, located between the compound eyes. The distinct head has chewing mouthparts directed downward. The jaws are used for emerging from the pupa (PYU-pa), or cocoon, and for defense, killing prey, and nest construction. Bees have the combination of chewing and sucking mouthparts, allowing them to drink nectar from flowers.

All four wings are similar in texture, but the forewings, or those in front, are usually longer than the hind wings. The hind wings have a row of hooks along their leading edges that attach to the hind margins of the forewings while the insect is in flight. The legs are usually long and are used for running. In some species the legs are also used for digging. The mid-section, or thorax, of sawflies and their relatives is broadly attached to the abdomen. However, ants, bees, and wasps have threadlike waists. In these groups the threadlike segments are made up of the first few segments of the abdomen. Winged species have four membranelike wings with relatively few veins.

The ovipositors, or egg-laying tubes, of hymenopterans have special sensory structures that help the female to find good places to lay her eggs. In some ants, bees, and wasps the ovipos itor is not used for egg laying. Instead it is used as a defensive stinger. The stinger is hollow like a syringe and is capable of delivering a painful and venomous sting. The stingers of ants, wasps, and most bees are smooth so that they can be used repeatedly. However, the stings of honeybees can be used only once. Their barbed stingers remain in the flesh of the victim. As the honeybee pulls away, the stinger and internal organs are ripped from the abdomen and the insect soon dies.

The bodies of bees have several special features that allow them to collect pollen. Their bodies are covered with bristly and branched hairlike structures. The hind legs of many bees have special bristles that form either a brush or a basket allowing them to carry pollen. Leaf-cutter bees use brushes on the undersides of their abdomens for carrying pollen.

The larvae (LAR-vee), or young form, of sawflies and their relatives resemble caterpillars. They have distinct heads, three pairs of legs, and fleshy cone-shaped false legs on their abdominal segments. In all other Hymenoptera the larvae are wormlike and lack both legs and a distinct head. In parasitic species the mature larva is wormlike, but the previous stages may be very different in appearance. Parasites are completely dependent on other living organisms, or hosts, for food. Parasitic hymenopteran larvae spend their entire lives on the host. Their feeding activities usually do not kill the host.

The features of adult hymenoptera are clearly visible in the pupae (PYU-pee), or life stage between larvae and adults. The legs and developing wings are not firmly attached to the body along their entire length. Some species pupate within a silk cocoon.

GEOGRAPHIC RANGE

Hymenopterans are found on every continent except Antarctica. There are about 115,000 species of hymenopterans worldwide, with about eighteen thousand in the United States and Canada.

HABITAT

Hymenoptera occur in a wide variety of habitats where they are found in the soil and leaf litter or on grasses, shrubs, and trees. Most species are active on warm, sunny days, but some species are active at night, especially those that attack prey that are also active at night.

DIET

Most adults feed on pollen, nectar, and plant sap, as well as honeydew, the sugary waste produced by aphids, mealy bugs and hoppers (Hemiptera). Both adult and larval leaf-cutter ants depend on a special fungus as their primary source of food. The ants grow the fungus themselves in special underground chambers. Other hymenopterans eat living or dead animal tissues, especially insects. Many female parasitoids (PAE-re-SIH-toyds) feed on the body fluids of insects in order to produce eggs. Par-asitoids are hymenopterans with lifestyles in between parasites and predators (PREH-duh-ters) that hunt for food. Parasitoids feed inside the body of a single living host, eventually killing it.

The larvae of most sawflies and their relatives feed on plant tissues. They feed on the outside of plants, but some bore into stems, fruits, and leaves. Horntail larvae bore through living tree trunks and rely on funguses to break down the wood so they can use it for food. Parasitic or parasitoid wasp larvae eat the tissues of their host insects. Other wasps live and feed in plant galls (gawls). Plant galls are swellings or abnormal growths that appear on roots, stems, leaves, and flowers. Infections, insects, mites, and other organisms produce galls. Many wasps feed their larvae chewed-up or paralyzed (PAE-ruh-laizd) insects and spiders. The paralyzing stings of these wasps do not kill the insects or spiders. Instead, the sting has chemicals that affects their nervous systems and prevents them from moving.

BEHAVIOR AND REPRODUCTION

Only some ants, bees, and wasps sting. In these species only the females can sting. They use their egg-laying tubes, or ovipositors, to deliver a painful venomous sting that burns and itches. The burning is caused by an acid that is released into the wound with the venom or poison.

The larvae of parasitoid wasps spend their lives with their hosts, while the adults are free to move about the environment. Using special chemicals produced inside their bodies, some par-asitoid larvae paralyze their larval hosts and stop them from growing. In other species they allow the host larva to continue to feed and grow so that it reaches maximum size, but it will die before reaching maturity. Depending on species, parasitoids either feed on the inside or outside of the bodies of their hosts. Some species feed alone, while others attack their hosts in groups. There are even some hymenopteran parasitoids that attack other hymenopteran parasitoids.

The larvae of many wasps live as parasitoids inside the bodies of insect larvae. The adults freely move about the environment and are often seen on flowers. For example, female scoliid wasps attack beetle grubs in their burrows or underground pupal cases. After laying her eggs, the females leave. The larvae will hatch, feed, and develop without any assistance. These and other wasps may or may not use their stings to paralyze their larvae's future hosts.

Other wasp females must first locate, capture, and paralyze food for their larvae, usually caterpillars, crickets and katydids, and spiders. They then drag their victims to a cavity or crevice (KREH-vuhs) in the ground or stuff them into previously built nests. Metallic blue or green cuckoo bees, which are actually thick-bodied wasps, do not construct nests and rely on the food stores of other hymenopterans to feed their young. Potter wasps build a potlike mud nest and lay their eggs inside. Then they provide the nest with all the paralyzed spiders necessary to feed their young through pupation and seal it with more mud. Hornets, paper wasps, and yellow jackets continue to feed their larvae as they develop. Many bees also continue to feed their young as they develop, but they give them pollen and nectar instead of insects and spiders.

All ants, but only some bees and wasps, are truly social insects. Social insects live in colonies with multiple overlapping generations that share the duties of rearing the young, gathering food, defending the colony, and expanding and repairing the nest. The labor is divided among different castes, or forms. The worker caste takes care of most of the nest chores. Some species have a soldier caste. Soldiers are larger, more powerfully built individuals that defend the nest. Workers and soldiers are always sterile females and are unable to mate or reproduce. Only members of the reproductive caste, queens and males, can mate and reproduce. The males are short-lived and die soon after mating. Queens mate one or more times before they start a new colony and never have to mate again. They will store enough sperm in a special sac in their abdomen to fertilize thousands to millions of eggs. Social hy-menopterans use mud, leaves, and chewed-up bits of wood that are formed into paper or a paperlike material to build their nests.

Males of parasitic species usually look for emerging females in places where their hosts live. They will sometimes fight with other males to defend these sites. Others form mating swarms to attract females. In most hymenopterans, the females release pheromones (FEH-re-moans), chemicals that are very attractive to males of the same species. Courtship is common among ants, bees, and wasps and involves touching each other with antennae (an-TEH-nee), or sense organs, and vibrating legs and wings.

The life cycles of hymenopterans include four very distinct stages: egg, larva, pupa, and adult. In some parasitic species, a single egg will develop into several individuals. In many species females determine the sex of their offspring by controlling which eggs are fertilized. Fertilized eggs become females, while unfertilized eggs develop into males. They can also speed up or slow down the growth of their populations by producing females or males.

Sawflies and their relatives lay their eggs on or in leaves, stems, wood, and leaf litter. The females of some sawflies will stand guard over their egg masses until they hatch. Mature larvae pupate inside plant tissues or in the soil. Most species produce only one generation each year and overwinter, or last through the winter, as larvae.

Parasitic and parasitoid females search for and select the right host by using highly sensitive organs on their antennae and ovipositors. Some females will use only one host or a few closely related host species. Others will lay their eggs on a variety of similar hosts, such as caterpillars, in a specific habitat. Most parasitoids lay their eggs on or in the body of the host. The females often have long ovipositors to lay eggs in cocoons, burrows, and other protected places.

The larvae of sawflies and their relatives molt, or shed their exoskeletons, or hard outer coverings, up to eight times before becoming a pupa. Females sometimes molt one more time than the males of their species. In all other Hymenoptera the larvae molt up to five times before reaching the pupal stage.

HYMENOPTERANS AND PEOPLE

Hymenopterans have long been a part of human culture. In ancient Egypt bees and wasps symbolized various gods. The ancient Greeks called the bee Melitta the Goddess Honey Mother. One of the largest ants in the world, Dinoponera, was used as a symbol of strength for several tribes in the Amazon. The Mixe people of Oaxaca, Mexico, believed that they would become more powerful if they ate ants and considered them symbols of courage, patience, and strength.

In modern times the Russian composer Nikolai Rimski-Korsakov (1804-1908) was inspired by the buzzing of flying bees and composed the famous "Flight of the Bumblebee." This music was written for strings and is performed as part of the opera, The Tale of Tsar Saltan, the story of a prince who is turned into a bee. Several Pokemon cartoons include characters inspired by hymenopterans.

Hymenopterans are also considered to be beneficial to humans. Many species of para-sitoids and predators are used to control insect pests in gardens, agricultural fields, and managed forests. Bees are important pollinators. Honeybees also produce honey, which is used in the making of all kinds of foods. Beeswax is used for making candles, cosmetics, lip balm, polishes, and sealing wax.

In some parts of the world hymenopterans are considered an important part of the human diet. Boiling them breaks down their venom and softens their stings. Many species of ants and ant larvae are not only eaten but are considered to be a real treat. Aborigines, native people of Australia living in the desert, dig up honey pot ants as a source of sugar. Some of the workers of these ants spend their lives in underground chambers as living honey pots. When food is abundant, special workers are continually fed honeydew and nectar by other ants until their abdomens swell to the size of a small marble. They store the sweet stuff during times of plenty and feed it to their nest mates when food is scarce. Honey pot ants also live in the western United States and Mexico.

Hornets, paper wasps, and yellow jackets are often considered a nuisance when they build their paper nests on or near homes and office buildings. Nest-building Hymenoptera can be domestic nuisances. They inflict painful stings to protect their nests. Some people are highly allergic to stings and may die if stung. Southern imported fire ants have burning stings and are

THE MYTH OF THE WHITE ANT

Termites are sometimes called "white ants," but they are not ants at all, nor are they closely related to them. Most ants are dark and hard-bodied, while termites are soft and pale. Ants have a narrow waist, while termites are thick-waisted. Ants have antennae distinctly bent like an elbow, while those of termites are short and beadlike. Moreover, worker ants are always females, while worker termites are both males and females.

considered a nuisance if their colonies are established close to homes and parks. Their nest mounds sometimes make it difficult to use harvesting equipment in some agricultural fields. They also attack and kill nestlings and other small animals and can have a devastating effect on the local populations of all kinds of animals, including other insects.

Only a few species of Hymenoptera are considered pests that harm forests and crops. Sawfly larvae cause damage to forests, orchards, and ornamental trees. Wood-boring larvae, in association with funguses, can cause extensive damage to plantations of fir trees. A few ant species are also considered pests. For example, the leaf-cutter ants strip crops and garden plants of their leaves and flowers. Other species protect other crop pests, such as sap-sucking insects, from predators and parasitoids.

CONSERVATION STATUS

One hundred and fifty-one species of hymenopterans are listed by the World Conservation Union (IUCN). Three species are listed as Critically Endangered, or facing an extremely high risk of extinction in the wild; 139 are Vulnerable, or facing a high risk of extinction in the wild; 7 are Near Threatened, or likely to qualify for a threatened category in the near future; one is Data Deficient, which means there is inadequate information to make a direct or indirect assessment of risk of extinction; one is Least Concern, or does not qualify for a threatened category.

Like all organisms, hymenopterans are particularly sensitive to the misuse of pesticides and habitat destruction. All humans are especially dependent on the pollination services of bees and wasps. The reduction or loss of their populations will greatly hurt efforts to grow vegetables, fruits, and flowers, as well as fodder for domestic animals.

HONEYBEE

Apis mellifera

SPECIES ACCOUNTS

Physical characteristics: Workers measure 0.37 to 0.62 inches (9.5 to 15.8 millimeters) in length, while male drones are 0.62 inches (15.8 millimeters), and queens are 0.75 inches (19.5 millimeters). Their bodies are golden brown and black, with bands of pale orange or yellow on the abdomen. The head, antennae, and legs are nearly black. Fine, hairlike structures cover the thorax and appear less so on the abdomen. The wings are clear. Honeybees have special bristles on the outside of the back legs that form pollen baskets.

Geographic range: Honeybees are found on all continents except Antarctica.

Habitat: Colonies of honeybees often live in manmade commercial hives, but wild colonies generally prefer tree hollows and other sheltered spaces.

Diet: Adults and larvae eat honey and a mixture of honey and pollen called beebread. The larvae of queen bees are also fed royal jelly, a

This honeybee has pollen attachted to its leg. (©James H. Robinson/Photo Researchers, Inc. Reproduced by permission.)

nutritious substance produced by special glands located in the heads of the workers.

Behavior and reproduction: Honeybees are social insects that live in colonies made up of a queen and up to eighty thousand workers. During the warmer months there may also be a few hundred males or drones. The queens live four or five years. They lay up to two thousand eggs per day or about two million in a lifetime. The drones mate with new queens. The workers care for the queen and young, forage for food, defend the colony, and expand the hive, by building new combs. The combs are made from wax produced as flakes from special glands in each worker's abdomen. The workers use their jaws to shape the wax into cells and combs. Each comb is made up of two layers of six-sided cells and hangs straight up and down in the nest. The cells are used to rear the larvae and to store honey and pollen. Queen cells are built at the lower edges of combs and are peanut-shaped. Honeybee colonies live for several years. The queen and workers spend the winter inside the hive.

Honeybees form new colonies by swarming. Just before the new queens emerge from their cells, the old queen leaves the hive with about half the workers to search for a new site to start a hive. The new queens fly into the air to mate one or more times with different drones. They will return to the hive of their birth, but only one queen will eventually take over the hive. The other queens are stung to death by the ruling queen or by the workers.

Unfertilized eggs develop into drones. Fertilized eggs develop into females, either workers or queens. Larvae develop into queens only if they are continually fed royal jelly by the workers.

Honeybees and people: Many crops around the world depend on honeybees for pollination. Honeybees are raised commercially to harvest their honey, wax, pollen, venom, and other products.

Conservation status: This species is not considered endangered or threatened. However, many populations have suffered serious losses due to mite infestations. ■

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