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Honeybee Anatomy

Honeybees are fascinating insects with a wide range of complex behaviours. This page details the most significant aspects of their anatomy: physical structure; senses; dietary requirements; digestive system; reproduction; respiration; circulation; and glandular functions.

Taxonomic Hierarchy

Apis Mellifera Western Honey Bee. Ranked: Species - Linnaeus, 1758. Further info on this nomenclature.

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Physical Structure

Image of a typical Western Honeybee female worker, colours vary greatly from yellow to almost black.

Main physical features of Apis Mellifera, the Western Honey Bee

The overall physical structure of the honeybee is that of a typical insect with a body that is in 3 main parts, has a hard chitinous exoskeleton on the outside, and all the organs and muscles to work the joints on the inside. The three main body parts are: the head, thorax and abdomen.

• The Head - bears a pair of antennae to facilitate smell, detecting vibration etc.; compound eyes with very good vision; ocelli to detect light; and mouth parts for both sucking and biting.
• The Thorax - is subdivided into 3 parts, each bearing a pair of legs (6 legs in total); the second and third parts also each bear a pair of wings (4 wings in total). The infertile female worker's rearmost legs are modified with hairs and spines on the tibia for collecting and transporting pollen (pollen baskets).
• The Abdomen - is subdivided into a number of segments each with a pair of spiracles for breathing, it has no appendages, but contains the reproductive apparatus at the tail end, and also in the case of the queen and workers, the stinging apparatus.

The whole body has a covering of branched hairs, more on the head and thorax than the abdomen. The hair covering, more visible on young bees, acts as an effective insulation but rubs off over time, older bees are then noticeably shinier in appearance. Sensory hairs between the compound eyes on the head are thought to detect air speed and direction, and to aid navigation.

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Senses - Smell / Taste

Bee olfactory senses are very well developed, and conversely they have a poor sense of taste. They are thought to have around 170 odorant receptors and their sensory organs include their eyes and antennae. Their sense of smell is acute, it is well developed both for location of food and also for detecting the pheromones which are emitted by other bees and control colony behaviour. Pheromones are a highly advanced method of communication among the social insects, and are chemical substances secreted by the bees to trigger a response from individuals of the same species, to influence their behaviour and the complex behaviours of the honeybee colony as a whole. Pheromones can indicate a range of situations and instructions: presence of queen; supersede the queen; attack mode; danger look out; entrance this way; follow me; food this way; swarm now; and so on. Because of this each colony has a distinct and identifiable odour to other bees, and recognise their own members as distinct from intruders - contributing to an effective colony defence system. With such a well developed sense of smell the need for an acute sense taste is less important, all necessary information coming from smell before reaching the mouth parts.

Senses - Sight

Bees have well developed vision, which is necessary and important for all castes of honeybee. They have 5 eyes altogether consisting of 2 larger multi-lens compound eyes on the either side of the head for excellent all round vision, and 3 small light sensitive ocelli on top of their head for detecting changes in light to help with escaping danger. The two compound eyes can see in detail at close range and can also sense movement and speed of movement at distance, fast moving objects are locked on to while while bee defences are alerted. Excellent sight is important for the queen in locating her hive before and after her mating flight, and for workers a keen sense of orientation which is largely visually based to help them orientate very accurately to their home location hive entrance by using a variety of recognised landmarks. Lastly for drones to be able to recognise the queen by sight and smell during mating activity. Its suspected that the eyes are probably not used inside the colony where it is virtually dark, and that they use their other senses to move around in the hive.

Senses - Navigation

Navigational sense is more a combination of sight and smell, a very keenly developed sense of direction in the workers. They must navigate accurately to find and re-find sources of forage, and they must also communicate the information regarding forage sources to the other foraging workers. Worker bees are able to accurately 'measure' both distance and direction, due to their ability to recognise the direction of polarisation of light which is dependent on the relative position of the sun. By a combination of repeated movements on the comb known as the 'bee dance', can tell other workers of the distance, direction, type and quality of a potential source of forage. In effect this ensures a continuous workforce appraisal of the best sources of forage, its location, and efficient use of the workforce.

Senses - Touch

Bees use their antennae and other sensory hairs on their body to provide a keen sense of touch, which is used, in conjunction with their sense of smell inside the hive to navigate and locate different areas, brood, stores etc. They also use their sense of touch to accurately measure everything inside the hive, helping them construct comb and modifying the inside structure of the hive with great precision to ensure the all important 'bee space' is maintained.

Senses - Hearing

It is widely understood that bees do not have ears so don't possess the ability to hear as humans do. However they most certainly have the ability to detect and respond to sounds. Queens in particular can make some quite specific sounds such as the 'piping' of virgins inside their cells before and after emergence, it follows that these sounds are intended to be 'heard', and can be equally detected by other bees, and that they respond to them. It is not yet proven but likely that the bees detect sound vibrations with the second and very sensitive segment of their antennae, and by organs in their hind legs.

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Diet

In evolution, honeybees were originally members of the Wasp family, but later evolved alongside flowering plants to become a distinct group of species feeding exclusively on pollen and nectar while the wasps continued to feed their young on chewed up insects. Plants need to transfer pollen from flower to flower in order to reproduce and survive, so by using a variety of means to attract the bees and by offering them a reward in the form of pollen or nectar, their success is achieved. Producing flowers, nectar and pollen as a means of attracting the bees is quite costly to the flower in terms of effort but in order to ensure fertilisation it is a worthwhile trade-off. For the bees the rewards constitute a complete diet: pollen for protein; and nectar for carbohydrates. Further to these two essentials they only need access to water.

Worker honeybees are specially adapted to collect both the pollen and nectar from the flowers. They suck the nectar up using their tongues (proboscis), collecting it in a pre-stomach or crop in order to transport it back to the hive. The pollen is gathered using their front legs and then compressed into pellets that are carried on the hind leg 'pollen baskets'. These baskets when loaded are quite visible on the worker bees.

To make honey from nectar, the bees add enzymes to the nectar from their saliva and other glands. These enzymes chemically alter the sugars, and by fanning with their wings they evaporate off the excess water content from 90% down to about 20%. This process changes the nectar into honey. With a water content of 20% or less the honey will not ferment, and possesses remarkable properties beneficial to the bees and humans alike. Nutritionally, 1 tablespoon of honey (21 grams) contains about 64 calories and 17 grams of sugar, including fructose, glucose, maltose and sucrose, and contains virtually no fibre, fat or protein. The honey is stored in the comb, wax cells which are impermeable to water and which are covered with a wax cap, where it remains hermetically sealed against moisture in the air.

Gathered pollen is also stored in the wax cells, and is preserved by adding some honey to it. The store of honey and pollen is therefore conditioned to be able to last through the winter. The honeybees tongues are relatively short, and only suited to certain types of flower. Typically honeybees visit plants that have a short tubed flowers, and are coloured either blue, yellow, or white in colour. Favoured plants often fall into one of a small number of flower families e.g. Liliaceae (Crocus, snowdrop), Crucifera (Cabbage Family - Oil Seed Rape, Mustard), Rose Family, Dandelion and Daisy families. They will however forage on any potential source of food or water, clean or otherwise.

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Digestion

The honeybee digestive system is a simple gut consisting of a single tube which can store and regurgitate nectar from a pre-stomach or crop, as well as digesting and absorbing honey and pollen. The indigestible remains such as the outer coating of pollen grains are normally excreted from the other end of the tube during cleansing flights. The mouth parts include an extendable hollow tube (proboscis)for sucking, and a pair of fairly blunt mandibles which are used in ingesting pollen, and in manipulating wax for fabrication into comb.

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Reproduction

Workers honeybees are females with ovaries that are reduced in size and functionality and don't normally try to lay eggs, however in a prolonged absence of the queen in the colony a few individuals will sometimes start to develop and then lay unfertilised eggs, which can only develop into drones. Laying workers usually lay more than one egg per cell, a sure sign of queen problems. Drone laying unsettles the colony and is a situation that can be difficult to rectify. The only part of the female sexual apparatus which is fully developed in the workers is the sting, and it is fully functional.

Queen's have female reproductive organs that are fully developed with ovaries that can produce a constant supply of eggs about 0.7mm in length, laying them one per cell. The queen mates with several drones on only one occasion during the first three weeks of her life, and stores the sperm from these matings within her reproductive system. If she fails to mate during this time, she will eventually start to lay eggs but these will be unfertilised and will only ever produce drones. While the queen's supply of sperm lasts she can lay fertilised or unfertilised eggs as required, depending on whether she lays into a drone or worker cell. If she fails to mate with sufficient drones on her mating flight, or her supply of sperm runs out, she will also become a drone layer, however queens have been known to successfully lay fertilised and unfertilised eggs for up to four or even five years.

Drones are designed only to produce sperm and mate with the queen during her mating flight, and die in the process. They have little other function in the colony besides mating duties, although their presence is regarded as essential for maintaining moral, and they may assist with heating and cooling brood. Later in the season when the colony is finished queen rearing activity for the year, few drones are tolerated in the hive and they are first denied access to food, then thrown out of the hive to die. Drones observed late in the season are indicative of a weak or failing queen.

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Respiration

Honeybees are living organisms, and as such need a supply of oxygen to the body to function and live. They take oxygen from the air around them, and without that supply of oxygen they will suffocate and quickly die. They breath by passing air through small openings on the sides of their bodies, each abdominal segment has an opening on each side which are called spiracles, that lead into a branching tube called the trachea. Oxygen and the metabolic by-product carbon dioxide are exchanged with body fluids across the walls of the tracheae, which permeate into the body tissues. Physical movement of the body helps push air in and out of the spiracles, which in turn facilitates efficient exchange of gases. Close inspection of returning forager bees can reveal a lengthening and shortening of the body as they 'breath' air in and out of the spiracles.

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Circulation

The circulatory system of the honeybee is complex, they have a long tubular 'heart' with an aorta lying along the length of its body, and their 'blood' is not like our human blood because it does not contain red cells for carrying oxygen and they don't circulate it in normal arterial and venal blood vessels. Instead bees have haemolymph, a combination of lymph and blood, which carries sugars and amino acids and other metabolites. Unlike the blood in mammals, the haemolymph is not pumped through blood vessels but fills the body cavity in an open circulatory system controlled by flaps and valves.

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Glands

Salivary Glands are found in the head and thorax of the honeybee workers, and saliva produced is discharged at the mouth. The saliva is a slightly alkaline watery liquid, and is used to dissolve sugary foods, and to wash surfaces free of them, and to soften substances being chewed. The hypopharyngeal gland found in the workers' head, is the gland responsible for producing brood food or royal jelly - a thick white milky substance, rich in sugars, proteins and other nutrients which is fed to young larvae, queen larvae, and the queen. In older workers the gland produces the enzyme which acts on the sugars in nectar changing it into honey. This gland develops as the worker bee ages, and changes in bee labour activities can be attributed to the stages of gland development.

Mandibular Glands in the queen mainly produce 'queen substance' - a pheromone produced only by the queen and which, as it is passed around the colony during mutual feeding and grooming, informs the colony that the queen is there. Her absence, and more importantly the absence of her queen substance, will be noticed within about ten minutes of her removal, or if she is starting to fail. It also helps the drones locate the queen during the mating flight. In addition, queen substance suppresses the development of ovaries in the workers, it suppresses the building of queen cells, and it promotes the building of worker comb as opposed to drone comb.

Nasonov Glands are only present in workers, at the dorsal posterior end of the abdomen, and are important for communication, for getting the attention of other bees, and for attracting other colony members to their location. When exposed by the worker the gland emits a pheromone which advertises the bees location, and can indicate the location of the colony entrance, or settling position for a swarm, and overall conveys the message - 'come here'. When honeybees use this gland the exposed part of their abdomen is clearly visible, and they accompany the exposure with wing fanning to disperse the pheromone.

Sting Scent is a substance smelling strongly like pear drops or acetone, and is emitted from glands in the sting apparatus. The scent communicates to other bees the simple message - 'sting this'. The sting scent is strong and carries a distance attracting bees from in and around the hive to join in the stinging, and will attack any moving thing in the vicinity. When it appears during hive manipulations it is advisable to stop further activity. The scent from a sting is strong and remains active on gloves and overalls long afterwards.

Wax Secreting Glands are present on the workers only, there are 8 glands in total found on the underside of the last four ventral abdominal segments, which secrete scales of wax that are picked up by the legs, then passed to the mandibles where they are chewed and mixed with saliva before being sculpted into honeycomb in the frames. This is rarely seen during normal hive manipulations as the production of wax is generally carried out during night time hours. Younger bees produce larger scales, their ability decreasing as more and more daily flights cause atrophy of these glands.

Wax scales ready for use in building comb. Usually difficult to see on the underside of the abdomen. (This unfortunate individual was one of many recovered from a mini-nuc overcome by wasps!)

The production and secretion of wax scales used to build comb on the frames requires the nest to be warm, and requires the consumption of a considerable amount of honey - estimates vary considerably of the amount of honey needed to produce 1lb of wax, however a lot of heat is also generated by the bees during wax production making comb building a costly process in terms of energy, stores and bee-power for the colony. Swarms carry honey with them for this purpose, although the older flying bees produce less than the younger bees due to levels of atrophy.

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