Anatomy of the Bee

Bee anatomy studies the honey bee's body structure, made up of head, thorax and abdomen, together with its sense organs, glands and internal organs. This knowledge is not just theory: anatomy explains why smoke works, why varroa does so much damage, why nosema causes dysentery and why bees die after stinging.

What parts make up a bee's body?

The honey bee's body is covered by a hard exoskeleton made of chitin and consists of three main parts:

• Head: Eyes, antennae, mouthparts, brain and some important glands.
• Thorax: Three pairs of legs, two pairs of wings and powerful flight muscles.
• Abdomen: Digestive and excretory organs, fat body, heart, wax glands, scent gland, reproductive organs and sting.

The narrow "waist" between thorax and abdomen is formed by the first abdominal segment fusing with the thorax; this lets the bee bend its abdomen freely. The branched hairs covering the body both collect pollen and sense touch and air currents.

What is on a bee's head?

Eyes

The bee has two large compound eyes and three small simple eyes (ocelli) on top of the head. The compound eye is made up of thousands of small units; it detects movement, shape and colour. Bees see ultraviolet, blue and green light and perceive red as a dark colour. Because they also detect polarised light in the sky, they can find the direction of the sun even in cloudy weather. The ocelli measure light intensity.

Antennae

The antennae are the bee's "nose and fingers": they sense smell, touch, temperature, humidity and vibration. In the dark hive they are the main sense organ. Females have 12 antennal segments, males 13; the male antennae are specialised for detecting queen pheromone from a distance.

Mouthparts

• Mandibles: Used for working wax, building comb, carrying propolis, cleaning and defence.
• Proboscis (tongue): Used to suck up nectar, water and honey; folded under the head when not in use. Tongue length differs between bee races and affects the use of deep flowers.

Glands in the head

• Hypopharyngeal (royal jelly) glands: Well developed in young workers; they produce a large part of the food for larvae and the queen.
• Mandibular glands: In the worker they contribute to royal jelly; in the queen they produce the queen pheromone that holds the colony together.
• Salivary glands: Play a role in processing food and softening wax.

The bee brain is small but its learning ability is strong: it remembers colours, scents and landmarks and memorises the position of its hive. It is because of this memory that foragers return to the old spot when a hive is moved.

What is in a bee's thorax? Wings and legs

The thorax is the bee's "engine room". It is largely filled with flight muscles. The bee produces heat by shivering these muscles without beating its wings: this is how the warmth of the winter cluster is maintained and the brood nest is kept at around 34–35 °C.

• Wings: There are two pairs. In flight, small hooks on the leading edge of the hind wing lock onto the forewing and the two wings work as a single surface.
• Front legs: Carry a notch used to clean the antennae.
• Middle legs: Help with walking and unloading the pollen load.
• Hind legs: In the worker they carry the pollen brush, pollen press and pollen basket.

There are also breathing holes (spiracles) on the sides of the thorax. Acarapis woodi (the tracheal mite) enters through the first pair of these and lives and reproduces inside the air tubes in the thorax.

What is in a bee's abdomen?

Digestion and excretion

1. Honey stomach (crop): Nectar and water are carried here. It is separated from the digestive section by a valve; the bee can regurgitate its contents in the hive.
2. Midgut: The main digestion and absorption take place here. Nosema spores multiply in the cells of this section.
3. Hindgut and rectum: Faeces accumulate here. In winter the bee holds its faeces for weeks and empties them on a cleansing flight on a mild day. Nosema and poor winter food upset this balance; dysentery appears inside the hive.
4. Malpighian tubules: Work like kidneys, filtering out waste.

Fat body, heart and blood

The fat body is a nutrient store; it plays a central role in immunity, detoxification and winter endurance. The long life of winter bees depends largely on this tissue. The Varroa destructor mite feeds mainly on this tissue; that is why bees emerging from varroa-infested brood are short-lived and prone to disease.

The bee's blood (haemolymph) circulates not in vessels but in the body cavity; a tube-shaped heart running along the back pumps this fluid forwards.

Glands and reproductive organs

• Wax glands: Four pairs on the underside of the worker's abdomen; at a certain age they secrete thin wax scales.
• Scent gland (Nasonov): At the tip of the abdomen; releases the orientation scent that guides bees home.
• Reproductive organs: The queen has well-developed ovaries and a sperm store (spermatheca); in the worker the ovaries are rudimentary.

How do bees breathe?

The bee has no lungs. Air enters through ten pairs of spiracles on the sides of the body and reaches the tissues directly through branching air tubes (tracheae). There are air sacs in the abdomen; the bee pumps air by contracting and relaxing its abdomen.

This system explains why ventilation is vital during transport: in a closed, hot hive the bees heat up quickly, oxygen runs short and the colony can suffocate.

How does a bee's sting work?

The sting is a modified egg-laying organ; that is why it is found only in females (queen and worker) and not in drones.

• Worker bee: Her sting is barbed. When it lodges in mammal skin it does not come out; it tears away together with the venom sac and muscles, and the bee dies.
• Queen: Her sting is smoother and curved; she uses it against rival queens and can withdraw it.
• Alarm pheromone: The pheromone released from the sting area summons other bees to the same spot.

Differences between queen, worker and drone

What does knowing anatomy give the beekeeper?

• Smoke: It suppresses the antennae's detection of alarm pheromone; that is why it is used sparingly and where needed.
• Clothing and scent: Bees react more to dark, hairy and moving objects; light-coloured clothing and unscented skin make inspection easier.
• Varroa: Damage to the fat body shows why the late-summer mite load determines the winter.
• Nosema and dysentery: Gut health is linked to the quality of winter food and to cleansing flights.
• Pollen colours: The colour of pollen loads gives a clue as to which plants the bees are visiting at the time.