Honeybee – Apis mellifera
By: Jaclyn Costanzo
The honeybee is an incredible and often misunderstood insect. Not only do they impact the majority of the world’s agricultural and wild crops and plants, they also exhibit social structures and communication that far exceed what one might expect from such a diminutive species. What the honeybee lacks in size, they make up for in importance. Unfortunately, the honeybee has experienced a dramatic decline in the last several decades due in part to a number of environmental and human factors. The fate of the honeybee rests in limbo, making it even more important to understand this amazing creature and the invaluable role it plays in the world’s complex ecosystems.
The honeybee, genus is known for its production and storage of honey within perennial, colonial nests, or hives, made of wax note. There are twenty-six recognized subspecies of honeybees, differentiated by morphology, molecular variances, habitat, behavior, and output.
Honeybees vary in size, depending on their roles within the nest. Sterile females, known as workers, are the smallest honeybees, growing to an adult size of 10-15mm in length. Adult males (drones) measure 15-17mm long, and fertile adult females (queens) reach a mature size of 18-20mm long. Honeybees are easily identified by the alternating bands of orange/yellow and black that stretch across their abdomens (useful in warning potential threats.) Their thorax and abdomen are covered in hair, the abdomen tending to have less hair. Pollen baskets, compartments used to store pollen during collection, are located on the dark reddish-brown hind legs. Honeybees have five sets of eyes, three of which are used as light sensors and located at the top of the head, and two with compound lenses. Drones have the largest eyes, believed to aid in locating queens during mating. Honeybees have two sets of wings, which tend to be largest on worker bees. Both workers and queens have stingers that are supplied with venom from glands located in their abdomens1. Bees typically do not sting unless provoked or in defense of their nests or young2. Workers can only sting once in their lifetime since their stingers are barbed and fatally tear away from their body (along with the venom glands) after the sting3.
Honeybees only forage during the day when temperatures and weather conditions are ideal (they will not fly in extreme heat, high winds, or heavy rain and are unable to fly in temperatures below 10°C,) but are active throughout the day within the hive. They are endothermic and are able to warm their bodies and raise the internal temperature of the hive by exercising their flight muscles4. This action is also used to remove the excess moisture from fresh nectar, which needs to be brought from 70% water down to 17% water to produce honey. Honeybees fly at speeds up to 15mph, beating their wings nearly 200 times per second. In a single trip, a honeybee may visit between 50 to 100 pollen sources5.
Honeybees are social insects that live in cooperative hives made of complex cellular structures formed from wax secreted from workers’ bodies. These colonies tend to grow from 10,000 to 15,000 inhabitants in the spring and peak at more than 50,000 inhabitants during the summer, when a queen is in her prime and able to lay up to 3,000 eggs in a single day (assuming she is of good health.)6
Honeybees are divided into three main groups: workers, drones, and queens.
Workers are sterile females and are the bees most often seen outside the hive. Their responsibilities and behaviors within the colony change as they age (known as age polyethism.) New workers clean and prepare cells for food and egg storage. Within a few days, the workers responsibilities change to waste and debris removal, fanning within the hive to regulate air circulation and temperature, processing nectar, and feeding the larvae and queen from glands located within their heads and bodies (this behavior continues into the next behavioral stage.) Within the second week of life, wax glands within the workers’ bodies become active and they begin building and repairing the cells within the hive. These cells are hexagonal and made of wax. Each cell can store one larva, pollen, or honey. The workers then become responsible for guarding and protecting the hive. They survey each bee that enters, driving away strangers and predators. During the fourth week of life, workers; food and wax glands shut down and their sole responsibility becomes foraging7.
The male bees within the colony are called drones. A drone’s sole purpose is to mate with the hive’s queen, although only one in a thousand drones will actually succeed. In a single hive (during the spring and summer) there may be several hundred drones. However, in the winter conditions make it harder for the hive to sustain as many bees so the drones are sometimes expelled.
The third type of bee is the queen. She is integral to a hive’s survival. Not only does the queen lay the eggs (upwards of 3.000 a day during hive build-up in the spring,) she also produces chemicals that regulate the activities of the other bees within the hive. Generally, there is one queen in a hive. When one queen dies, workers will feed one worker “royal jelly” (an elixir that causes the worker to develop into a fertile female – see diet.)8
Each hive has a unique chemical signature that allows bees to recognize hive-mates and be in constant chemical communication with each other (regarding the health of the colony and queen, for example.) Most communication between honeybees is based on chemical signals, specifically taste and scent. Honeybees are able to communicate the location of food supplies by receiving the scent of the food from a returning forager. These returning foragers also communicate the location of food sources through dance. The round dance is used to indicate the presence of food within 300 meters of the hive, while the more complex waggle dance communicates the distance and direction of food further than 300 meters from the hive (using the sun’s position as well as the bees memory to relay the information.) Another instance in which chemicals, or pheromones, communicate information is when a worker stings an enemy. After the stinger and glands are torn from her body, pheromones are released that alert other bees from the hive about the potential threat and help them locate the enemy. Sight is also as important sense for honeybees. They are able to interpret their surrounding environments, recognize threats, spot flowers and food sources, and detect ultraviolet rays (helpful in locating the sun on cloudy days and spotting specific markings on flowers.) A specialized portion of their eyes enables honeybees to see polarized light, useful in navigation. Lastly, vibrations within the hive are important communicative tools. Both workers and queens can sense and create vibrations used to communicate information regarding the behaviors of the queen, the emergence of a new queen, the location of food sources, etc.
Honeybee queens may live up to five years, but on average live between two and three years 9. Workers may experience a lifespan as short as six to eight weeks during their peak production period in the summer. During this period, a worker may fly the equivalent of 1.5 times the earth’s circumference, and as a result, burn out their wings 10. Drones on average live between four to eight weeks.
Honeybees choose habitats that offer ample food sources, such as meadows, gardens, and open wooded areas. They also have success surviving in deserts, grasslands, and wetlands as long as there is water, food and shelter available. Honeybees build their nests within natural cavities.
Within their habitats, honeybees face many predators. Crab spiders, orb-weavers, and several species of wasps are known to attack and wipe out honeybee hives in one blow. Other predators known to attack hives include toads, opossums, bears, honey badgers, birds, skunks, anteaters, chimpanzees, gorillas, rodents, and some ants.
Honeybees are native to Africa, Europe, and western Asia. Starting in the 17th century, Honeybees were introduced by humans into non-native locations, including North and South America, Australia, and eastern Asia. Today, honeybees can be found around the globe (expect for Antarctica and extreme northern climates.)11
Honeybees are herbivorous and workers forage during the day for pollen and nectar for the whole colony. They favor food sources that are close to the nest but may travel as far as 8 miles for food or water. They suck up nectar with their tongues and store it in their, the anterior section of their digestive track. They collect pollen and store it in their pollen baskets, specialized structures located on their hind legs. In moving from one food source to another, honeybees play invaluable roles as pollinators, transferring pollen and seeds from one plant to another, allowing cross-pollination and fertilization to occur. Honeybees, along with other pollinators, affect roughly 30% of the world’s crops and around 90% of the world’s wild plants12. They are opportunistic and have been known to steal from other hives. During the winter months, honeybees (and their larvae) survive on stored pollen and honey and secretions from members of the hive.
After foraging, workers return to the nest and transfer the nectar and pollen to younger workers. These workers are responsible for feeding members of the colony and creating long-term food stores. They secrete specialized enzymes into the honey that allow the water to evaporate and the sugars to concentrate. After eating the pollen and nectar, these young workers are able to secrete royal jelly and worker jelly from glands in their heads. This jelly is fed to the larvae and determines what roles they will later fulfill in the hive (workers or queens.)
Mating occurs during mild weather in the spring or summer. It commences when male honeybees (drones) leave their hives and gather at “drone assembly areas.” Virgin queens, who become sexually mature at five to six days old, emit pheromones as they fly through these areas to attract drones from miles around. Mating occurs in the air and often results in the formation of a, as a cluster of drones surround the queen who are attempting to mate. A virgin queen may mate with up to ten males (from her own hive or other hives,) during each of up to four mating flights she will make during her mating period. These consecutive flights constitute the entirety of a queen’s mating activity for her entire lifetime. Males who succeed in mating die within a few hours or a few days of mating. Other males will stay in the assembly area waiting to mate or until they die. For the rest of her life, a queen bee will lay eggs continuously, typically 1,000 eggs per day and as many as 200,000 in her lifetime. Queen bees in cold climates may cease egg laying for a period of time in the late fall.
Honeybees are holometabolous, meaning they go through four life stages: egg, larva, pupa and adult. Depending on temperature, the eggs hatch in one to six days. Their sex is determined by the queen, who has the ability to lay fertilized or unfertilized eggs. Unfertilized eggs have a haploid set of chromosomes and develop into males or drones, while fertilized eggs have a diploid set of chromosomes and develop into female honeybees (whether they become workers or queens is determined later.) A queen will adjust the type of eggs she is laying depending on the health of her hive and the ratio of males to females within it. Small white grubs emerge from the eggs and stay within their individual wax cells, where adult worker bees feed them. The role a female honeybee plays as an adult is determined by whether she is fed royal jelly as a larva. The female larva that do not receive royal jelly (and will grow into workers) and male larva are fed a combination of pollen, nectar, and honey. The length of the larval stage depends on the type of larva (four to five days for workers, six to seven days for drones, and six days for queens.) At this point, the larva are sealed into their cells, where they molt, spin a cocoon, and transform into a pupa. During the pupa stage, larvae undergo a metamorphosis into an adult honeybee. This process takes twelve days for workers, fourteen to fifteen days for drones, and seven to eight days for queens. Upon completion of this stage, adult honeybees chew their way out of the cells and begin life in their designated roles. Worker bees take a total of three weeks to reach maturity and have a life expectancy of six to eight weeks (although they may live as long as eleven months if they survive during a winter.) Drones take twenty-four days to reach maturity and will only live for four to eight weeks (they do not survive the winter.) Queen bees take sixteen days to reach maturity and live for two to five years.
In addition to individual reproduction, healthy colonies may reproduce too. This event is called swarming and happens one or two times a year, at the start of seasons that produce the most nectar. Swarming commences when workers produce multiple queen larvae. Before the new queens emerge, the original queen flees the hive, taking up to half of its inhabitants with her. This new colony will temporarily nest in a tree while scouts find an adequate location for a permanent hive, where they will build new honeycomb and begin reproduction and food collection. Depending on the number of new queens that emerge in the original hive and the number of inhabitants in the hive, the first few queens that emerge may leave the hive with “afterswarms” and build new hives elsewhere. If the population of the hive is not large enough to produce afterswarms, the emerging queens will fight until only one queen remains, at which point she will begin laying eggs.
Typically the queen is the only bee in the hive that is able to lay eggs (because she secretes pheromones that prevent workers from becoming fertile.) However, in the event that a hive becomes queenless, workers may begin laying unfertilized eggs13.
Notes of Interest
One colony of bees (generally numbering around 30,000 bees) is capable of pollinating one acre of fruit trees.
Nearly two million flowers must be visited in order to produce one pound of honey.
In one flight, a honeybee will visit between fifty and one hundred flowers.
In her lifetime, a worker gathers enough to produce 1/10 of a teaspoon of honey.
The nectar gathered by honeybees is nearly 70% water, while honey is only around 17% water 14.
Honeybees, both wild and domestic, are susceptible to a number of natural health threats, including parasites, pathogenic microbes, at least eighteen different viruses, bacteria, and fungi. One of the most prevalent diseases in domestic hives is Nosema disease, which is cause by Nosema apis, a protozoan. Many of the viruses that cause disease in honeybees are associated with parasitic mites. Within the last twenty years, two specific species of mites have wreaked havoc on the world’s domestic and wild honeybee populations. The first, Acarapis woodi, is a small mite that feeds on bee hemolymph (a fluid in invertebrates that functions like blood) within the tracheas of adult bees. This mite weakens adult bees and may cause whole colonies to fail during cold weather when bees are confined to the hive. This mite was first discovered in European populations, but its exact origins are unknown. The second mite, Varroa destructor, has had a much more severe impact on honeybees. This mite originated in Asian Honeybee colonies but quickly spread to other domesticated honeybee colonies in eastern Asia. This mite is now prevalent on every continent, except Australia. This mite affects a colony in several ways. Young mites feed on larvae and pupae within the hive while adult mites feed on adult honeybees, leaving open wounds. In addition to feeding on honeybees, this mite is also known to carry several viruses that are detrimental to a colonies health. Mite infestations are believed to be at least partially responsible for wiping out almost all of the wild North American colonies, as well as many domestic colonies. The small hive beetle, Aethina turnida, is another threat to honeybees. The beetle larvae consume all the contents of the hive, including the comb, pollen, honey, eggs, and larvae15.
In addition to mite infestations and disease, honeybee populations around the world are succumbing to a number of human factors. Global warming is causing a shift in blooming seasons, resulting in an imbalance between honeybee’s food collecting periods and the availability of food sources. Agricultural pesticides, commonly used by farmers to kill pests, may also harm honeybees. Agricultural, commercial, and residential development has also negatively impacted honeybee populations. Not only are honeybees losing habitats, they are also losing native food sources, which are being removed or replaced by species that are not beneficial to pollinators.
Because of these factors, both environmental and human, bee populations have reached a fifty-year low in countries like the United States, where nearly 1/3 of colonies have vanished. In addition to a sharp decline in honeybee health, within the last decade, farmers and beekeepers have noticed a startling number of healthy adult honeybees abandoning their hives, leaving the queen and adolescents unattended. This phenomenon, referred to as Colony Collapse Syndrome, is believed to partially result from the aforementioned factors but is still not fully understood, making it the topic of much research because of the important role honeybees play in ecosystems and agriculture around the world16.
For more information on honeybees and Colony Collapse Syndrome, check out these sources:
http://www.abfnet.org – American Bee Keeping Federation