Honeybee Anatomy
Although the anatomy of the honeybee (apis mellifera) varies depending on their role in society, there are five components that are the same in workers, drones and queens:
- The hard outer shell (exoskeleton).
- Workers, drones and the queen all have three main body parts, i.e. the head, thorax, abdomen
- All honeybees have a pair of antennae attached to their head.
- Every bee has three pairs of legs and
- two pairs of wings.
Honeybees are cold-blooded and are not able to control their body temperature automatically. The inside of the hive requires a constant temperature of 32 ± 0.6 C regardless of the outside temperature. Honeybees maintain this temperature through behavioral control.
To generate heat, they contract their flight muscles repeatedly without moving their wings. For cooling down, they pump their abdominal system to circulate more air through their spiracles (an external respiratory opening) and trabeculae (a series of partitions formed by bands or columns of connective tissue). This process evaporates more water and lowers the bees temperature.
Shape and Size
How can you tell the difference between a female (worker) and a male honey bee?
To differentiate between drones and female honey bees, examine their physical characteristics. Male bees, called drones, have large eyes that touch on the top of their heads and are slightly bigger than female worker bees. They also have 11 segments on their antennae’s flagellum, while female bees have 10. Drones do not possess stingers due to the absence of modified ovipositors. Their main responsibility is to mate with the queen bee. Conversely, female workers have smaller eyes that are separated on the sides of their heads and have 10 segments on their antennae flagellum. Their ovipositor is modified to act as a stinger, which they use to protect the colony.
Queen bees have a different body shape than workers or drones and are also much bigger, but this is just one of several differences.
Head
Eyes
Honeybees have 5 eyes in total, 2 larger compound eyes and three simple eyes. The compound eyes are like a cluster of around 3,000 to 9,000 individual mini eyes or optical units. Excellent in detecting motion, they allow insects to see images from the front, the back and sides without having to rotate their heads. They generally have only a short range of detail vision, meaning they can only see sharp images a few millimeters ahead.
Unlike compound eyes, the three ´simple eyes´(ocelli) only have one lense similar to a human eye. They detect even the slightest changes in light levels and help bees to navigate during the day by orientating themselves by the sun. Drones eyes are twice the size of those of worker bees and queens.
Antenna
The antennae located on the head above the compound eyes and on either side of the simple eyes allow honeybees to touch, smell, taste and even ´hear´. Drones antennae are each made of 13 segments, while workers and queens only have 12 segments.
The antennae has mechanoreceptors that provide honeybees with a sense of touch. For years it was believed that honeybees are unable to hear. However, scientists have since learnt that the antenna is able to respond to vibrations of frequencies caused by moving air particles, an ability that can be compared with hearing.
The antennae also have 170 receptors to detect odors, which provide honeybees with an excellent sense of smell.
Another function of the antennae is to communicate with other bees through touch. For reasons yet unknown, honeybees rely primarily on the right antennae to communicate.
Mandibles
Honeybees use their powerful jaws (mandibles) for biting, manipulating wax and pollen, and digging. The mandibles protect the mouthparts, such as the proboscis and other organs. While drones and the queen have pointed mandibles, workers have smoothed mandibles designed to help in producing wax.
Bees are divided into two groups based on the the length of its proboscis (tubular tongue) that is used to collect nectar from flowers, clean their hairs or groom one another. Honeybees with a long proboscis can easier collect nectar from long-necked flowers, whilst those with a shorter one prefer single petal or shallow petalled flowers.
Brain
Honeybees brains consist of several lobes with less than a million neurons. Their brain gives them an extraordinary capacity to process information and make decisions. Scientists have discovered that bees understand the concept of zero and can do basic math.
Pappus of Alexandria, the last physician, geologist and mathematician of Antiquity already discovered that bees have a concept of calculating when he stated, “Bees… by virtue of a certain geometrical forethought knew that the hexagon is greater than the square and the triangle and will hold more honey for the same expenditure of material.”
A new discovery suggests that honeybees may also be capable of connecting symbols to numbers, which could pave the way for humans to communicate with bees.
Thorax
Wings
The thorax is the center of movement and features two pairs of membranous wings. It has 3 segments that are separated by a pair of spiracles for letting in air.
Attached to the thorax are two pairs of wings that twist like a propeller with each up- and down stroke. Bees can achieve speeds of 25km per hour (15.5 mph), and flap their wings around 200 times per second. All honeybees have larger front wings than hind wings to stabilize their bodies and manouvre. The wings of all three casts are adapted to their body shape. Drones have larger and broader wings than workers, while the queen has slightly longer, elongated wings than drones.
Bee Legs
All honeybees have six legs, i.e. two front legs, two middle-, and two hind legs attached to the thorax. The front legs are designed to clean the antennae.
Honeybees have a good grip on rough and smooth surfaces. The claws on the last tarsomere allows them a good grip on rough surfaces, like tree trunks for example. The ability to walk on smooth surfaces like leaves and even glass is because of the soft pad called arolium.
The hind legs of the worker bee are different to those of a queen or drone. Workers have pollen baskets attached to the tibia. When visiting flowers the bees groom themselves, brushing the pollen that sticks to their body towards their hind legs into the pollen basket. The bees mix the pollen with some nectar to make it stick better, while the coarse hair on the pollen basket prevents the pollen from falling out.
Abdomen
The abdomen of female honeybees and drones look similar from the outside apart from their size but are different internally. The female abdomen is divided into six segments, while drones have seven. In honeybees the abdomen also contains the wax glands.
Stomach
Honeybees have two stomachs; One for eating food, and the spherically shaped crop or honey stomach that is located behind the first stomach. The crop store stores the nectar from the flowers to take back to the hive. When the crop is full, it can expand to such an extent that the abdomen swells. Back at the hive, honeybees regurgitate the stored nectar from their stomach into honeycomb cells. To remove the moisture, they fan it with their wings and the result is honey!
Stinger
Female honeybees also have a stinger. As the name suggests, the stinger is the honeybee´s biggest weapon of defense. Honeybees are typically not aggressive and only sting as a last resort. Workers usually die after stinging their enemy. This is because their stinger is barbed and sticks in the victim where it continues to pump poison into it. In contrast, the stinger of a queen is smooth, allowing her to use it several times although she mainly uses it in battle with other queens.
Reproductive Organs
The stinger of female honeybees also has a reproductive function aside as a matter of defense. The organ is modified to also deposit eggs. Queen bees have a spermatheca, a sack like structure used to store all the sperm she collects from various drones during her typically single mating flight. Her ovaries mature and start producing eggs. Those that are fertilized develop into worker bees while unfertilized eggs become drones.
Drones sexual organs have two reproductive functions; To produce around 10 million sperm cells that are all identical to the egg they grew from (haploid egg), and to mate with a queen to fertilize her eggs. The genealogical tree of drones is highly unusual in that they only contain one set of chromosomes from the mother (haploid). Diploid cells contain two sets of chromosomes, one from the mother and one from the father.
Drones therefore technically only have a mother but no father. If one follows back the generations of drones, an interesting pattern emerges. This sequence is known as the Fibonacci sequence of which each number is the sum of the two preceding ones, starting from 0 and 1.
The 1st generation back has only has one member, ie. the queen (F). The second generation back consists of 2 members, i.e. a drone (M) and a queen (F). The third generation back has 3 members, the forth has 5 members, the fifth generation back has 8 members, the 6th 13 members, the 7th generation 21 members, resulting in a sequence of 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144…and so on.
Wax Glands
Unlike the queen and drones, worker bees also have four pairs of wax-producing scales on the underside of the abdomen that secrete liquefied wax. When exposed to air, the wax hardens into thin scales. To make one single gram of wax, workers need to create approx. 1,000 scales. Considering that it takes one worker around 12 hours to produce 8 scales, it would theoretically take one bee 62.5 days to produce 1 gram of wax