1. Head

1.1 Antenna(e)

Honey bee antenna with its three segments labeled

Because honey bees live inside tree cavities (natural) or hives (man-made), both of which have little light away from the entrance. Smell and touch therefore are much important for them than visual when inside the colony.

The honey bee antennae (one on each side) house thousands of sensory organs, some are specialized for touch (mechanoreceptors), some for smell (odor receptors), and others for taste (gustatory receptors). It used to be thought that honey bees couldn’t hear any airborne sound because they do not have pressure-sensitive hearing organs (like our ear-drums or similar structures on the legs of katydids). Because of this, scientists were puzzled the ways through workers can perceive the buzzing sound produced by workers during waggle dances. About 10 years ago it was discovered that bees can indeed ‘hear’ airborne sound in close range, this is through sensing the movement of air particles by the hairlike mechanoreceptors on the antennae. This discovery helped the construction of robot bees that can be directed to dance (by a computer) inside a hive and guide workers to a specific location.

1.2 Eye(s)

Honeybee eyes. A – Two compound eyes. B – Three simple eyes. From "Beekeeping in Tennessee"

1.3 Mouthparts

1.3 Internal organs

Honey bee mandibular gland. (c) Zachary Huang

The main internal organs in the head are the brain and subesophageal ganglion, the main component of the nervous system, in addition to the ventral nerve cord that runs all the way through the thorax to the abdomen. Yes, the bee does have a brain, a pretty sophisticated one too. The brain has a large area for receiving inputs from the two compound eyes, called optic lobes. The next largest input are from the antenna (antenna lobes). One important region in the middle of the brain is called the “mushroom body” because the cross section resembles two mushrooms. This area is known to be involved in olfactory learning and short term memory formation, and recently shown to be also important in long term memory formation in insects.

There are also endocrine organs attached to the nerve cords, very close to the esophagus (the food canal). One is called the corpora allata (CA, in Latin it means the body beside the food canal), which is the only source of one important hormone, juvenile hormone, which is involved in both the queen-worker differentiation, and also division of labor in workers. The other one is called corpora cardiaca (CC, the body near the heart), which is a neurohemal organ and stores and releases another hormone (PTTH, prothoracicotropic hormone). PTTH can stimulate the production of ecdysteroids, by a gland located in the thorax, the prothoracic gland.

Lastly there are exocrine glands inside the head also, most notably the mandibular glands, the hypopharyngeal glands and the salivary glands. Mandibular gland is a simple sac-like structure attached to each of the mandibles. In the queen this is the source of the powerful queen pheromone.
In young workers the gland produces a lipid-rich white substance that is mixed with the secretion of hypopharyngeal glands to make royal jelly or worker jelly and fed to the queen or other workers. In old workers (foragers) the gland also produces heptanone, a component of the alarm pheromone. Similarly hypopharyngeal glands produce protein-rich secretions when young (nurses), but produce invertase (an enzyme to break down sucrose into fructose and glucose) in foragers. The glands is consisted of a central duct (which is coiled between the front cuticle and the brain) with thousands of tiny grape-like spheres (acini, singular: acinus). The secretion flows to the mouth through the long duct. The glands are large in size (hypertrophied) in nurse bees but become generated in foragers. There is also a pair of head salivary glands inside the head. The glands produce saliva which is mixed with wax scales to change the physical property of wax.

Honey bee hypopharyngeal gland. (c) Zachary Huang

Honey bee salivary gland. (c) Zachary Huang

2. Thorax

2.1 Legs

On the front leg, there is a special structure used for cleaning antenna (when too many pollen grains stuck there), properly called the “antenna cleaner”.

2.2 Pollen Basket

2.3 Wings

The front wings are larger than the hind wings and the two are synchronized in flight with a row of wing hooks (humuli, singular: humulus) on the hind wing that would hitch into a fold on the rear edge of the front wing.

Close-up of hooks that hold the wings together

The flight muscles exposed

The wings are powered by two sets of muscles inside the thorax, the longitudinal and verticle muscles. During flight, when the longitudinal muscles contract, the thorax raises its height, so the wings are lowered because of fulcrum like structure (pleural plates) near the wing base. Conversely, when the vertical muscles contract, it shortens the height of thorax, raising the wings. The honey bee flight muscles can contract several times with one single nerve impulse, allowing it to at a faster rate.

3. Abdomen of the Honey Bee

On the surface the abdomen has no special outside structures, but is the center for digestion and reproduction (for drones and queens). It also houses the sting, a powerful defense against us humans.A worker, a drone, and a queen can be distinguished by the size and shape of their abdomen. The queen pictured here was laying eggs, as can be seen by her large abdomen.