How Bees Work

Scientists suspect that bees and flowering plants both evolved around 100 million years ago, in the middle of the Cretaceous period. Before this period, many plants reproduced the way today's conifers do. They released seeds and pollen using cones. The wind carried the cones, and eventually the pollen came into contact with the seeds and fertilized them. During the Cretaceous period, some plants began to reproduce using flowers. Unlike conifers, these plants, called angiosperms, needed the help of insects and other animals to reproduce. Insects had to physically move pollen grains from plants' anthers, or their male structures, to their stigmas, or female structures.

At about the same time, bees differentiated themselves from their wasp-like ancestors. Prehistoric wasps were carnivores that lay their eggs in the bodies of their prey. Bees became herbivores, eating pollen and nectar from the newly-evolved plants and pollinating flowers as they went. Fossil evidence supports this theory -- the oldest known bee fossil is 100 million years old, and the preserved bee has several wasp-like features. This doesn't necessarily mean that bees evolved from wasps. It's more likely that bees and wasps both evolved from a mutual, wasp-like ancestor.

Today, bees still have several physical features in common with their wasp cousins. They also share some traits with ants. Together, bees, wasps and ants make up the insect order Hymenoptera, which means "membranous wings."

A bee's body has a lot in common with the bodies of other insects. Much of it is covered in an exoskeleton made from small, movable plates of chitin. A bee's body is also covered in lots of fuzzy, branched hair, which collects pollen and helps regulate body temperature. The body also has three sections -- the head, the thorax and the abdomen.

The head houses the brain, a collection of about 950,000 neurons. These neurons are specialized, and they communicate with specific neighboring neurons. This division of tasks is part of why a bee's brain, which is a fraction of the size of the bee's head, can perform complex tasks that might ordinarily require a bigger brain. A system of nerves allows the brain to communicate with the rest of the body.

On its head, a bee has two sensory antennae. It also has five eyes -- three simple eyes, or ocelli, and two compound eyes. The compound eyes are made of lots of small, repeating eye parts called ommatidia. In each compound eye, about 150 ommatidia specialize in seeing patterns. This allows bees to detect polarized light -- something human beings cannot do.

Like most insects, a bee has complex mouth parts that it uses to eat and drink. The sizes and shapes of these parts can vary from species to species, but in general, most have:

The labrum and maxillae are like lips. They support a proboscis, or tube for collecting nectar.

A bee's two pairs of wings and three pairs of legs connect to its thorax. The wings are extremely thin pieces of the bee's skeleton. In many species, the front wings are larger than the back wings. A row of hooks called hamuli connect the front and rear wings so they beat together when the bee is flying.

We'll look at bee legs and the one part everyone remembers -- the stinger -- in the next section.

The legs have the same basic parts as other insect legs. Beginning with the part closest to the bee's body, they are the coxa, trochanter, femur, tibia and tarsus. These parts act basically like the bee's hip, thigh, shin and foot, and tiny joints separate each segment. A bee's legs can also have several specialized structures, including:

The abdomen has almost no appendages, but it houses nearly all of the bee's internal organs. Passageways called spiracules allow the bee to breathe, and a network of tubes and tracheae carry oxygen into the bee's body. An aorta in the thorax pumps blood, or hemolymph, directly over the organs rather than through a system of vessels. Oxygen floats in the hemolymph without the use of red blood cells, so the fluid is colorless instead of red. The abdomen also holds a tube-like digestive system that includes a crop, or honey stomach, where the bee holds nectar.

A bee's abdomen does have one notable appendage -- the stinger, which is a modified ovipositor, or egg depositor. This stinger combines a poison sac with sharp lancets, which deliver the venom that the bee produces using its venom gland. Many scientists believe that bees inherited their venom from their wasp-like ancestors, used their ovipositors to lay their eggs in the bodies of other insects. Eventually, the substances that coated the ovipositor became venomous, which made it easier for prehistoric wasps to subdue prey.

Bees don't lay their eggs in meat, but they retain the ability to sting to defend themselves. However, some bees don't have stingers. Ovipositors are female reproductive organs, so male bees usually can't sting. There are also several species of stingless bees, which do not have stingers at all.

Several honeybee species have barbed stingers, which stick in the bodies of mammals, pulling out part of the bee's abdomen when she flies away. As a result, the bee dies. Bees with barbed stingers can often sting other insects without harming themselves. Queen honeybees and bees of many other species, including bumblebees and many solitary bees, have smooth stingers and can sting mammals repeatedly.

In addition to its venom, a bee produces a number of useful substances in glands located throughout its body. The types of glands vary considerably depending on the species of bee and how it lives. We'll take a look at the different types of bee and how they use the substances their bodies produce in the next section.

In scientific terms, bees are in the insect superfamily Apodiea. This superfamily includes lots of families, subfamilies, tribes and approximately 20,000 bee species. The bees in each family have traits in common, like methods for building nests. Different species usually have different physical traits, like wing shape or tongue length.

Many people are most familiar with honeybees and bumblebees. These are both social bees -- they live in large groups. Social bees use waxy secretions from their bodies to build large nests and containers in which to store food and raise young. A third type of social bee is the stingless bee. Stingless bees are native to tropical areas, where some societies use them for honey production. Until recently, stingless bee husbandry was common in the Mayan regions of South America, but the practice has nearly disappeared in the last 20 years.

Although honeybees and bumblebees are both social, their societies differ considerably. Honeybee colonies, or hives, are perennial. A queen and her daughters use wax from the wax glands on their abdomens to build a nest that lasts them for generations. If the hive becomes overcrowded, the workers, who are all female, will raise a new queen by feeding her royal jelly from a gland on their heads throughout her development. The old queen will leave the hive with about half of the workers in order to build a new nest, and the new queen will stay behind. The bees know that they need to raise a new queen when they stop receiving enough queen substance - a pheromone that the queen produces in her mandibular glands.

Bumblebees, on the other hand, have annual nests. Each year, the queen mates in the fall and then spends the winter underground. In the spring, she emerges and builds a nest in which she lays eggs. When her daughters hatch, they become workers, and they help the queen enlarge the nest. At the end of the summer, the queen lays eggs that hatch into new queens and male drones. The drones gather at a mating site in order to mate with the queens from various colonies, and the cycle continues.

Many people are most familiar with social bees because they can be more visible than solitary bees. Many social species produce substances that people use, like honey and beeswax, and people can see large groups of social bees feeding in orchards and gardens. But most bees aren't social -- less than 15 percent of bees live in colonies. The rest are solitary. They may exhibit some social tendencies, but they don't build large hives or store lots of extra honey. Instead, they build small nests that are big enough to hold a few eggs or a single egg. Sometimes, lots of solitary bees build their nests close together, but with the exception of mating and the occasional group defense of the nest site, these bees do not usually interact with each other.

Lots of solitary bees are known for how they make their nests. They may use cerumen, a type of wax secreted from their bodies, or propolis, a glue bees make from tree resins. Many bees add other materials to these substances. For example:

Other bees take advantage of existing materials when they build their nests. Some use empty termite hills or wasp nests. A few species lay their eggs in empty snail shells, either dividing the cell into chambers using glandular secretions or laying one egg in each shell. A few bees, known as cuckoo bees, are parasitic - they lay their eggs in the nests of other bees. Some cuckoo bees don't have any structures for collecting pollen, since they rely on other bees' pollen to feed their young.

Other solitary bees are known for the types of flowers they frequent or other distinguishing traits. Tiny sweat bees, for example, are attracted to people's sweat. Orchid bees are brightly colored and often have a metallic appearance. Scientists believe that orchids and orchid bees have co-evolved so that the two are now dependent on one another. Orchid bees have a very long proboscis, and orchids store their nectar very deep within their blossoms. Orchid bees are one of the few species in which the males perform productive activity other than mating. In some species, male orchid bees collect fragrant oils from blossoms using scraper-like segments of their legs. Since the female orchid bees do not collect these oils, scientists believe that the males may use them to attract a mate.

While social and solitary bees have considerable differences in how they live and build nests, they have a lot in common when it comes to reproduction. We'll look at the bee life cycle in the next section.

Regardless of whether they live alone or in groups, most bees have a similar approach to mating. In nearly every species, a male bee's only job is to mate with a female. Most male bees do not even have the structures necessary to make wax or carry pollen, so males in social species cannot contribute to the daily work that goes on in the hive. In fact, female honeybees usually force surviving males out of the nest before winter or when food becomes scarce.

Usually, a female bee mates with several male bees in midair, gathering all of the sperm she will need in her lifetime -- a few months for a solitary bee, or up to five years for a honeybee. Mating typically happens at a collective mating site, although scientists have not yet discovered how male bees choose a site. In some species, including honeybees, the males die shortly after mating because they leave their endophallus in the female's body, fatally injuring themselves in the process. In other species, males can mate with multiple females. Since females use sperm from several males to fertilize their eggs, this gives the male bees a better chance to father young.

After the female mates, she either retreats to a shelter for the winter or returns to her nest to lay eggs, depending on her species. Once she lays eggs, the eggs go through the same stages as caterpillars and butterflies do. First they hatch into larvae. The larvae eat before spinning cocoons and becoming pupae. They then emerge from the cocoons as adults.

Even though the steps are the same, the environment in which the developing bee grows can vary considerably. In solitary bees, the female builds a nest, places food inside and lays an egg. The food may include a mix of pollen and nectar called bee bread. It may also include a form of honey. Exactly how the bee positions her egg and its food varies depends on the species of the bee, as does the construction of the nest itself. Some bees lay one egg in each nest, while others divide their nests into multiple brood chambers. In nests with multiple chambers, male eggs usually go in the front, allowing young male bees to travel to the mating site before the female bees hatch. Many solitary bees seal their nests after laying eggs and never see their young. Often, these species lay eggs in the fall -- the eggs hatch in the spring, but the mother bees do not survive the winter.

Social bees, on the other hand, have a different approach to raising young. While a female solitary bee lays only a few eggs in her lifetime, a queen honeybee lays thousands. She places one egg into each cell in the brood area of the hive. The queen bee has control over whether she lays male or female eggs, and she lays male eggs in slightly larger cells. If she uses stored sperm to fertilize the egg first, the larva that hatches is female. If she leaves the egg unfertilized, the larva that hatches is male. This means that female bees inherit genes from their mothers and their fathers while male bees inherit only genes from their mothers.

Once the eggs hatch, the youngest worker bees in the hive take care of them. For the first two days of the larvae's lives, the workers feed them royal jelly. After that, the larvae eat pollen or bee bread. The only exception is the queen bee -- when the workers raise a new queen, they feed her royal jelly until she spins her cocoon. Bee larvae molt several times before spinning cocoons, at which point the workers cap their cells with tiny plates of beeswax to protect the developing brood.

The length of a female honeybee's life depends on when she emerges from her cocoon. If she emerges in the early spring, she may only live for a few weeks as she prepares the hive for lots of new bees. Workers who emerge later may live through the winter. But no matter when she is born, a female honeybee starts her life as a nurse, taking care of other bees. As she gets older, she begins to perform other important duties around the hive, such as cleaning out empty cells. She also learns to make honey and forage for food. We'll take a look at the tools that bees use to find and store food in the next section.

Bees find food the same way other animals find food -- through sensory input and an understanding of the features of their environments. Bees have an acute sense of smell, and they can remember and recognize patterns, such as the patterns of colors that are likely to be near good food. They can also recognize symmetry, a trait that scientists typically associate with more intelligent life forms. All of these abilities help bees find and recognize flowers, which produce the pollen they use for protein and the nectar they use for energy.

A solitary bee's life and the life of her young depend on her ability to find food, gather it and return it to the nest. For a scouting social bee, her colony's survival depends on the same things, as well as her ability to tell her hive mates how to find the food. Some social bees do this by marking a trail with aromatic flower oils or by guiding their hive mates part of the way. Honeybees tell their sisters how to find food, water, resin and new nest sites using one of the most-studied animal languages -- dancing.

When a honeybee scout finds food, she uses two known tools to understand where it is. One is her solar compass, which lets her remember where things are in relation to the sun. The bee's ability to see polarized light lets her determine where the sun is regardless of whether it is obscured by clouds. The other tool is her internal clock, which lets her keep track of how far she has flown. Her internal clock also lets her determine of how much the sun moves during her journey. In other words, when she returns to the hive, she can tell her sisters exactly where the food is in relation to the current position of the sun, not the position of the sun when she found the food. As a bee matures, she also learns about how the sun's path across the sky changes during different seasons of the year and at different latitudes if her hive is moved. She can incorporate these changes into her measurements.

When she returns to the hive, the scout bee recruits her sisters to carry the food back to the nest. They, like the scout, are the oldest bees in the hive. The scout distributes samples of the food, which will help her sisters find the food when they reach their destination. Then, she performs a dance on the vertical surface of the combs in the hive. The area on which she performs the dance is commonly known as the dance floor, and the worker bees who observe the dance are followers.

If the food is nearby, the bee performs a round dance by traveling in loops in alternating directions. The round dance doesn't convey much information about exactly where the food is. However, it's generally close enough that the worker bees can smell it fairly quickly.

When the food is far away, the scout performs a waggle dance. During the waggle dance, the scout runs in a straight line while waggling her abdomen, and then returns to the starting point by running in a curve to the left or right of the line. The straight line indicates the direction of the food in relation to the sun. If the bee runs straight up the hive wall, then the foragers can find the food by flying toward the sun. If she runs straight down the wall, then the foragers can find the food by flying away from the sun. As the dance progresses, the dancing bee adjusts the angle of the waggle run to match the movement of the sun.

The speed of the returning loops lets the other bees know about the quality of the food source, but the bees learn where to go by following the waggle run. By vibrating her wings and waggling her abdomen, the dancing bee moves a lot of air. The bees around her can feel this air movement. The ones directly behind her, where the air movement is greatest, get a clear idea of where to fly and how far to travel. Once they reach the described position, they begin flying in a search pattern until they find the food source. After that, they make up to a dozen trips back and forth between the hive and the food, remembering the food's position each time. During each trip, each bee can carry half her weight in pollen or nectar. If necessary, they perform a tremble dance, in which they run in many directions while trembling, to encourage the other bees to begin unloading nectar.

Bees in the hive unload the pollen and nectar and store it in the beehive's cells. These bees are younger than the foragers, but older than the nurse bees. It's up to these workers to determine when the hive has enough of a type of food or building material and to inform the foraging bees. They do this by changing the way they accept the material. If they accept it eagerly, the foragers know that the hive needs more. But if the workers are reluctant to unload the material, the foragers know that the hive has plenty.

In order to conserve space and preserve their food, bees transform the nectar into honey. The process gives honey some unique properties -- we'll look at them in the next section.

Honey starts out as nectar that bees collect from flowers. Basically, nectar is a reward that plants produce to attract pollinating insects and birds. It's a sugary fluid includes the aromatic oils that give flowers their scent, as well as other trace substances. Bees collect this nectar by drawing it through their proboscis and storing it in their honey stomach. Honeybees then carry it back to their hive in tiny, 40-milligram loads.

The foraging bees regurgitate the nectar and pass it to worker bees in the hive. These bees then gradually transform the nectar into honey by evaporating most of the water from it. Nectar is as much as 70 percent water, while honey is only about 20 percent water. Bees get rid of the extra water by swallowing and regurgitating the nectar over and over. They also fan their wings over the filled cells of the honeycomb. This process retains lots of sugar and the plant's aromatic oils while adding enzymes from the bees' mouths.

The finished honey is thick, sticky and very sweet. It contains several types of sugar, including sucrose, laevulose and dextrose. Its flavor and color depend on the flowers from which the bees harvested their nectar. Orange blossom honey, for example, tastes and smells faintly of oranges.

Bees use the honey for food and store enough to survive the winter. At first glance, bees don't appear to be very active or need much food during the winter. They leave their hives only to relieve themselves, since they do not defecate in their living space. But while inside the hive, the bees are doing a lot of work. They take care of the queen and heat the hive by trembling their wing muscles, much like humans' bodies try to warm themselves through shivering. They control the temperature of the hive in summer as well, by circulating air through the hive with their wings and by sprinkling the honeycomb with water.

Honey is a good source of food for bees for two reasons. First, its high sugar content provides the bees with lots of calories, which they burn warming the nest and caring for the queen. Second, its physical properties make it extremely resistant to bacteria:

Honey's high sugar content, flavor and antimicrobial properties make it useful to people as well. Today, it's used in home and commercial cooking, and medical research suggests that it may be effective at treating antibiotic-resistant organisms, particularly in open wounds. Neither of these is a new phenomenon -- people have been harvesting and using honey for more than 6,000 years. Historically, people have used it to sweeten food and make fermented beverages like mead. In addition, covering a wound with honey or honey-soaked bandages was a common practice before the development of antibiotics.

For these reasons, people have found ways to make it easier and more convenient to harvest honey from bees. Next, we'll look at how beekeepers provide homes for bees and harvest their honey.

Over hundreds of years, people have developed many types of manmade hives that provide shelter and living space for bees while making it easier to harvest honey. The most commonly-used model today is the Langstroth hive, developed by Lorenzo Lorraine Langstroth in the 1850s. Prior to Langstroth's inventions, people primarily kept bees in basket-, box- or log-like hives. Some of these had removable top bars from which the bees suspended their combs. Others had no convenient way for accessing or removing honey. Top-bar hives are still in use in some parts of the world, and Mayan beekeepers raising stingless bees still use log-like hives.

Langstroth discovered that it was possible for people to influence how bees built their combs by adjusting the amount of space between building surface. This area, known as bee space, allows bees to move around, care for young, build new honey combs and produce honey. According to Langstroth's theories, the ideal amount of space between honeycomb layers is between ¼ inch and 5/16 inch (6.4-7.9 millimeters).

The Langstroth hive uses a multi-layered structure and removable frames to encourage bees to build their hives in an orderly fashion and to make it easier for beekeepers to harvest honey. From the bottom up, the layers are:

Beekeepers usually use shallow supers rather than full-sized supers for honey storage because honey is relatively heavy. A shallow super weighs about 35 pounds (15.9 kilograms) when full, and a deeper super weighs closer to 80 pounds (36.3 kilograms). This makes it easier for the beekeeper to remove and replace the supers. Bees will continue to make and store honey as long as they have enough storage space, so removing filled combs and replacing them with empty ones is important to beekeeping. It's also important to make sure the bees have enough food for the winter -- for this reason, many bee keepers perform their last honey harvest in the late summer so that the bees can collect nectar and turn it into honey in the fall.

To harvest honey, beekeepers can remove the framed combs from the shallow supers and spin them in a centrifuge, or honey extractor. This removes the honey from the comb while leaving the structure intact. Since it takes about 20 pounds (9 kilograms) of honey to make a pound (0.45 kilograms) of beeswax for the hive, reusing combs generally makes it possible for beekeepers to harvest more honey.

This setup makes it relatively easy for a beekeeper to harvest honey without damaging the hive or hurting any of the bees. The beekeeper does have to be careful, though. Many beekeepers use a veil and gloves to protect their faces and hands from stings while working with their hives. Beekeepers also move very slowly when opening the hive and removing and replacing the frames. This is important since bees release an alarm pheromone when they are crushed or use their stingers. This pheromone encourages their sisters in the hive to sting anything nearby. Beekeepers can mask this pheromone with smoke from a bee smoker, which is essentially a set of bellows attached to a fireproof can with a nozzle at the top. The smoke also encourages the bees to stop working and start eating honey in case they have to abandon their hive due to fire. This makes it less likely that the bees will become agitated or defensive as the beekeeper works at the hive.

One colony of bees can include thousands of workers. To make lots of honey, these bees need very large food sources, such as orchards, large vegetable farms or other areas of dense, flowering foliage. But beekeepers, particularly those who have very large-scale operations, do not always live close enough to the right food sources to support all of the bees. Some supplement their bees' natural foods with manmade nectars and purchased pollen. Others rent their bees to farmers, who use them for crop pollination. Without the rented bees, the crops would not bear the necessary food.

This reliance on honeybees for crop pollination is one reason why many people are concerned about a phenomenon known as Colony Collapse Disorder (CCD). Next, we will look at the myths and realities behind CCD.

In the spring of 2007, news agencies began to report on a disturbing phenomenon in the bee population. According to reports, beekeepers were visiting their hives to discover that their bees had disappeared. Sometimes, the queen and a few newly-hatched bees were all that remained. The beekeepers found no evidence of predators that feed on bees, like wasps and mammals that like honey. They also didn't see a lot of dead bees or evidence of bee diseases like chalkbrood or foulbrood, which attack the developing bee larvae, or of any of the species of mites that attack developing or fully grown bees. Based on this evidence, it seemed unlikely that the bees had gotten sick and died. On the other hand, many beekeepers reported that moths, animals and other bees steered clear of the newly-empty nests, at least for a few days. This usually happens when bees die because of disease or chemical contamination.

Many of the news reports were alarming. They described beekeepers losing more than half of their bees and explained the importance of honeybees in the pollination of food crops. Some articles implied that the disappearance of the bees would lead to widespread starvation. Others quoted Albert Einstein as saying that humans would follow within four years if bees became extinct.

It's highly unlikely that Einstein ever made his now-notorious statement on bees, but Colony Collapse Disorder (CCD) is a real phenomenon. It has the potential to dramatically impact food and honey production, but it's more complex than some of the reports make it out to be. First, CCD has primarily affected domestic, commercial honeybees - those that are raised exclusively for producing honey and pollinating crops. It seems to affect bees from hives that are moved from place to place in order to pollinate crops. Commercial honeybees make up a tiny portion of the overall bee population. Other types of bees, including Africanized honeybees, do not seem to be affected.

This also isn't the first time that the population of honeybees has declined suddenly and unexpectedly. The populations of individual colonies can decline sharply during the winter as bees naturally die. In addition, beekeepers have reported sharp decreases in their hive populations several times in the last hundred years. In 1915, beekeepers in several states reported substantial bee losses. The condition became known as Disappearing Disease, not because the bees disappeared, but because the condition was self-limiting and did not recur.

Researchers never determined the cause for Disappearing Disease or subsequent declines in bee population. The causes of CCD are still unclear, and several possibilities have been ruled out because they are not present in all of the affected colonies. For example, beekeepers with affected colonies have different methods for feeding their bees and for controlling mites and other pests. Bees in the affected colonies do not seem to have come from the same bee supplier. The Colony Collapse Disorder Working Group, which is investigating the phenomenon, also does not suspect that genetically-modified crops are to blame.

However, there are some prevalent theories on the causes of CCD:

One common theory -- that cellular phones may be causing CCD -- has been widely discounted. This theory made the news in April 2007, after "The Independent" featured an article on a link between cell phones and bee disappearance. However, the study that "The Independent" cited was not related to cell phones. The researchers were instead studying the electromagnetic energy coming from the base units of cordless phones by implanting the bases directly in the beehives. A cordless phone uses a different wavelength of electromagnetic energy than cellular phones do.

Approximately 15 percent of the food Americans eat comes directly from honeybee pollination. Another 15 percent comes from animals that eat foods that bees pollinate. In other words, close to a third of the food that Americans eat currently requires honeybee pollination. Some articles claim that Americans will also lose their entire supply of meat without honeybees to pollinate their food. This isn't necessarily true. Some plants, like red clover and alfalfa, are a substantial food source for cows and other grazing animals. Bumblebees frequently pollinate red clover, and solitary alfalfa bees frequently pollinate alfalfa. In other words, the decline in honeybees does not necessarily mean that these plants will lose their pollinators.

It's not unusual for wild bees to be significant pollinators of wild plants and crops. In fact, until the 16^th century, there were no honeybees in the Americas -- wild bees, solitary bees and other animals did all of the necessary pollination of flowering plants. Spanish colonists introduced honeybees to the Americas to improve honey production. Although most people consider honeybees to be an asset, they are technically an invasive species.

Unfortunately, if honeybees were to become extinct, it would be difficult for wild bees to resume their role in pollinating food crops. There are a couple of reasons for this:

At this point, it's unclear exactly where the honeybee species is headed and exactly how the drop in population will affect the world's food supply. Although the drop in population may not lead to the sudden extinction of the human race, it is likely to have a substantial effect on what we eat if it continues.

To learn more about bees, honey and related topics, check out the links on the next page.