Head of a Bee

Specifically, the Head of a Worker Bee

For beekeepers, the honey bee’s head is about vision and perception, containing organs for vision, smell, touch, and ingestion (proboscis & mandibles), and housing the brain that coordinates behaviour. Worker bees have the hypopharyngeal gland for making royal jelly, drones have larger eyes & brains dedicated to mating flights and spotting the virgin queen during said flight. The head of queens is similar to a worker, with modifications to account for her lifestyle.

A non-Technical Summary of the Honey Bee Head

Simple vs Compound Eyes

Like most insects, bee vision is generated through five eyes: the two compound eyes and three “simple” eyes called ocelli.

The large, multifaceted compound eyes on the sides of the bee’s head are composed of hexagonal units called ommatidia. Each ommatidium captures its own image, and the bee’s brain compiles these into a mosaic-like picture (Wakakuwa et al., 2005). In navigation, the compound compound eye detects movement and polarized (vibrating) light patterns, which bees use for navigation. They also perceive ultraviolet (UV) light, allowing bees to detect the UV patterns on flowers while foraging.

The structure of the ommatidia are for detecting changes in light patterns (movement). Their eyes are ineffective at detecting stationary objects, generating a pixelated, less pixelated image when compared to the single lens of vertebrates. This specialisation aids them in navigation, foraging, and avoiding threats but makes them less effective at detecting lack of movement.

The simple eyes, Ocelli, are located on the top of the bee’s head in a triangular arrangement (Hung & Ibbotson, 2014). While they don’t form detailed images like compound eyes, they are sensitive to light intensity. Ocelli help bees maintain orientation with respect to the sun, even in cloudy conditions. Their role is for in navigation and understanding time of day.

In worker bees, compound eyes are of moderate size and are used extensively for foraging and navigation (Streinzer et al., 2013). In drones, the compound eyes are much larger and meet at the top of the head. They are specialized for detecting virgin queens during mating flights. Queen bees have the same compound eye as the worker bees, as they are less reliant on vision since she spends most of her life inside the hive laying eggs.

How the Bee Brain Perceives Light

Light entering the ommatidia in compound eyes is detected by photoreceptor cells. Signals from these cells are processed in the first two optic ganglia (lamina and medulla; Paulk et al., 2009). The processed information then travels to the lobula and lobula plate, where more complex processing occurs. Finally, visual information is sent to the brain, particularly the mushroom bodies and the central complex, where it is integrated with other sensory information.

How Honey Bees Keep Their Antennae Clean

The antennae are their primary sensory organs; detecting odors, vibrations and taste receptors (de Brito Sanchez, 2011). Chemoreceptors help bees detect chemical cues, enabling to distinguish between flowers, identify hive mates and communicate with other bees via pheromones (via queen mandibular pheromone; Mumoki & Crewe, 2021). Mechanoreceptors allow bees to sense air currents and touch, which are essential for flight and navigation, reducing (but not eliminating) the chances of bees entering the wrong hives. Bees discriminate between objects and surfaces using these receptors, which are vital in the darkness of the hive as it relays information about honey comb, brood comb or their fellow sisters (Schenier et al., 2005).

Thermoreceptors on the other hand, are for detecting temperature changes, tuned to detect deviations from the optimal conditions for brood rearing or storing honey within the hive. Amongst other factors, these thermoreceptors will determine whether a hive requires fanning, or clustering to maintain an optimal ~34-36°C (Junca & Sandoz 2015).

As worker bees spend a lot of time sticking their heads into flowers, their antennae are muddled with pollen, which impairs their perception of the world. To mitigate this, the forelegs of honey bees contain notches filled with stiff hairs that serve as antennae cleaners, with one notch in each leg. As pollen accumulates on the bee’s body, its forelegs brush it away from the eyes and antennae, whilst the mid and hind legs pack it into the pollen baskets (Amador et al., 2017).

The Mouthparts of Bees

The mouth parts are two: the jaw-like mandibles and the long “tongue” that is the Proboscis.

The mandibles serves a similar function to a jaw. It is used for used for chewing solids, processing pollen, shaping wax, carrying debris, and (in some bee species) for defence.

The proboscis is used for sucking up nectar from flowers, drinking water and exchanging food with other bees via trophallaxis. It is a three-part structure composing of:

• The Glossa, the actual “tongue” that extends and retracts.
• The Labrum and Labium, tissue that surround the glossa and help form the tube through which nectar is sucked.
• The Maxillae (no, honey bees do not have jawbones), the mouth parts that aid in manipulating food and are involved in the formation of the food canal.

Worker bees have the most developed mouth parts, as they are the ones conducting hive maintenance, nursing and foraging. Honey bees are generalist foragers and their proboscis is of moderate length compared to other bees, which allows them to access a variety of flowers for foraging (Melin et al., 2019). Any foraged nectar is stored in the honey bee stomach, whereas pollen is packed into the pollen baskets.

Both queens and drones have underdeveloped mouth parts compared to the worker bees. They do not feed themselves and rely on workers to provide them with food. The queen bee has stronger mandibles at a young age (uses it to emerge from her cell), atrophying as she matures and it falls into disuse.

How Honey Bees Taste

Sensory receptors on the mouthparts send signals to the subesophageal ganglion, a part of the insect brain responsible for processing taste information. From the subesophageal ganglion, the information is relayed to higher brain centers, including the mushroom bodies, where it’s integrated with other sensory modalities (de Brito Sanchez, 2011).

The Honey Bee Brain

The honey bee brain is made up from the fusion of three ganglia in the head:

• Protocerebrum, associated with the eyes and vision centers.
• Deutocerebrum, associated with the antennae.
• Tritocerebrum, associated with sensing internal stimulus, such as from basic bee body functions.

Two main structures within the bee brain are the Mushroom Bodies and Central Complex. The mushroom bodies are involved in the memory and learning capacity of bees, and are essential for sensory integration and processing sensory inputs (Farris, 2008 & Strausfeld et al., 2009). Where mushroom bodies process information, the output response is in the Vertical Lobes, and are involved in olfactory (scent-based) and visual learning in honey bees (Menzel, 2012, Plath et al., 2017).

The central complex plays a role in navigation and coordinating complex behaviours, providing movement in response to internal and external stimulation (Pfeiffer & Homberg, 2014). In other insects like cockroaches and fruit flies, this neural system controls walking, turning, and climbing behaviours (Martin et al., 2015; Triphan et al., 2010).

When a behaviour is learnt, the mushroom body processes the information and stores it as a memory. If a subsequent action is associated with this behaviour (flight, walks), the central complex sends the necessary signals to perform it. This was confirmed by the 2017 study of Plath & colleagues, who found that honey bees with impaired central complexes did not run from a shock stimulus when compared to the control. From a visual learning perspective, their work showed that the mushroom bodies are required for decision making in response to choice – in this case the “safe” or “stimulating” colours and shape or colour and its position.

Are There Differences Between Honey Bee Brains?

Yes, the brain of honey bees differ based on their castes, a result of hormonal and evolutionary adaptations to their specific roles (de Paula Junior et al., 2021).

Workers bees have a well-developed brain, and their mushroom bodies are particularly large. This is because they have a wide range of responsibilities, from foraging and communicating with hive mates to nursing and hive maintenance. Their brain is adapted for complex tasks, navigation, and processing large volumes of sensory information. Worker bee brains are highly neuroplastic, that is they can change over time and stimulation. Workers that become foragers show changes in their neural structure compared to bees that stay as nurse bees (Cabriol et al., 2018).

The male drone bees have a brain specialized for mating. Their optic lobes are well-developed, aiding in spotting queens during nuptial flights. Regions like the mushroom bodies are less developed compared to the female bees since drones don’t participate in tasks like foraging. Their primary function is to mate with a virgin queen, and their brains are optimized for vision and mating behaviours rather than learning, memory, or complex task processing (Roat & Landim 2010).

Queen bees have a smaller brain compared to workers, despite their larger body size, but not as small as a drone. Their reduced brain size reflects their limited exposure to the external environment and the reduced need for complex processing. Areas for sensory processing are developed for reproduction as they identify size and location of brood cells for egg laying.

Queen larvae have larger brains than worker bee larvae, and this shifts at adulthood when worker bees gradually become larger. However, as adults, the brain regions of worker bees (antennal lobe glomeruli and left mushroom body) have a larger mass compared to queen bees, highlighting the differences in adult functions (Groh & Rössler, 2008).

Honey Bee Nervous System

From (from Gullan & Cranston “The Insects”, 2nd edition)

The central nervous system consists of the brain and ventral nerve cord (analogous to the vertebrae spinal cord). It contains a series of segmented ganglia (nerve cell clusters) that process sensory information and direct motor functions.

The honey bee peripheral nervous system extends throughout the body and contains nerves that carry signals to and from the central nervous system. It provides sensory information to the CNS and transmit motor commands to muscles and other effector organs based on the stimulation.

The visceral nervous system controls digestion, excretion and respiration (similar to the autonomous nervous system in vertebrates; Amann & Constantinescu, 1990). The foregut and honey stomach is innervated by the frontal ganglia and the caudal ganglion innervates the hindgut. Due to its role in metabolism, the visceral nervous system is connected to the brain and endocrine system.

Bee heads have many sensory organs, from eyes to antennae. They can detect a broad range of environmental cues, from visual and olfactory signals to electromagnetic fields. These sensations are processed by the central nervous system to guide the bee’s behavior. The carries of these signals signals are neurotransmitters like octopamine, which are also involved in learning and memory.

How the Hypopharyngeal Gland Makes Royal Jelly

The hypopharyngeal glands are located in the head of the worker bees and are used to produce royal jelly. It is composed of numerous tubules that converge into a common duct and each tubule consists of secretory cells that produce the components of royal jelly (Richter et al., 2016).

The secretory cells in the tubules of the hypopharyngeal gland produce the proteins, sugars, and lipids that make up royal jelly. The substances from the hypopharyngeal gland combine with secretions from the mandibular gland to form the complete (reviewed in Ahmad et al., 2021). Once produced, worker bees feed larvae by regurgitating the royal jelly from their crop, where it’s stored after secretion.

This gland develops rapidly in young adult bees and reaches its maximum activity when the bee is 5 to 15 days old, a period when the bee serves as a nurse. The gland’s activity is mediated by pheromones from the queen and brood, with their presence stimulating the secretory cells to produce royal jelly.

Composition of Royal Jelly

Royal jelly is a complex substance composed of proteins, sugars, fats, vitamins, and other beneficial compounds (Jianke et al., 2010). Worker bees digest pollen and mix it with secretions from the hypopharyngeal and mandibular glands. The pollen provides the nutrients, while the glandular secretions add enzymes and other compounds.

Being more nutritious than bee bread, honey or the beekeeper’s supplemental feeding, all larvae are fed royal jelly for the first few days of their life (2-3 days after hatching; Knecht & Kaatz, 1990). Larvae designated to become queens are fed exclusively on royal jelly throughout their larval stage. This exclusive diet leads to the full development of the larva into a queen bee.

The Head’s Role in Honey Bee Anatomy

What is the purpose of head? To make decisions? To make royal jelly? To look, taste and hear? The smelling ability of bees is weaker relative to its vision (Kropf et al., 2014), and hearing is driven by changes in air pressure (Towne & Kichner 1989). The head is one part of the anatomy of bees, and along with the abdomen and bee thorax, enable a bee to complete its daily activities.

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