LITMIR.BIZ

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below).

Being invertebrates, honey bees have a rigid exoskeleton which defines their external shape (Figure 3.2). The bee body consists of three distinct sections: head, thorax, and abdomen. The head comprises the organs one would expect: brain, mouthparts, and sensory organs. All of the locomotory appendages are attached to the thorax and are paired (left and right); they include two pairs of wings (front and hind) and three pairs of legs. The abdomen contains the majority of the gastrointestinal tract and the reproductive organs. In the case of the female honey bee, the abdomen terminates in a sting apparatus.

Three distinct morphologies occur in honey bees: the drone (male), the worker (female), and the queen (female). Drones are distinguished by their rather large, plump contours, and large eyes. They are typically around 19 mm long. Drones do not possess a stinger. The queen's size depends upon if she is mated or not (average size of mated queen is ~20 mm long) and she is identified by her large, long abdomen. Her wings are short relative to her abdomen in contrast to the workers and drones, whose wings extend beyond the abdomen. Workers average 15 mm in length (Vidal‐Naquet 2015). See Figure 3.1.

      Unless otherwise noted, the following sections describe the features of the worker honey bee (Figure 3.2).

Head

      Eyes

The honey bee has a pair of large, “compound” eyes that are readily visible on the lateral aspect of the head (left and right), and three miniscule “simple” eyes, called the ocelli, that are arranged in a triangular pattern on the top of the head. Honey bees are remarkably “hairy” under magnification, and these hairs include the compound eyes (Figure 3.3).

Figure 3.1 A photograph showing the three members of the honey bee hive – drones, workers, and the queen.

      Source: Photo courtesy of Randy Oliver.

Figure 3.2 External anatomy of the honey bee.

      Source: Illustration by Patrick D. Wilson.

Figure 3.3 Magnified view of a honey bee compound eye. The hexagonal shape of the ommatidia are visible.

      Source: Photo courtesy of Jamie Perkins.

      The compound eyes are composed of approximately 5500 hexagonal “ommatidia.” An ommatidium can be thought of as an individual eye, each with a sensory (optic) nerve, that sends its own unique signals to the brain. Collectively, the input from these 5500 “eyes” compose what the honey bee “sees.”

Figure 3.4 The three ocelli are indicated by the small arrows.

      Source: Photo courtesy of Zachary Y. Huang.

      However, it is presumptuous to assume that the honey bee perceives its environment the same way we see or visually sense our environment. Although bees are considered to possess true color vision, the wavelengths to which a honey bee eye is sensitive ranges from 344 to 556 nm – a lower limit which supports the assumption that honey bee vision extends into the ultraviolet wavelengths (Kelber et al. 2003; Avarguès‐Weber et al. 2012).

The three ocelli, or simple eyes, are difficult to see without magnification. Each has a single lens, but each eye contains approximately 800 photoreceptors. The ocelli are believed to function simply as light sensors; they do not form an image (Figure 3.4).

Antennae are segmented sensory structures that in honey bees contain chemo and other sensory receptors. The honey bee's antennae provide direct tactile, thermal, and humidity information as well as sensing vibrations and detecting pheromones in the surrounding air (Figure 3.5).

      Mouthparts

The external mouthparts of interest in honey bees are the mandibles and the proboscis. Worker bees use their mandibles to manipulate such items as wax and pollen. Unlike the vertebrate mandible, honey bee mandibles move from lateral to medial and thus function as pincers.

Figure 3.5 Closeup of a honey bee antenna, showing the segments.

      Source: Photo courtesy of Jamie Perkins.

      The proboscis is a tubular structure used by the bee to suck in fluids such as nectar and water. In honey bees, the proboscis is formed by separate mouthpart components that combine to create a tube. In other nectar‐feeding insects such as butterflies, the proboscis is a dedicated tubular structure (Snodgrass et al. 2015) (Figure 3.2).

Thorax

      Wings

      Honey bees have two pairs of wings: front and hind, left and right. As mentioned above, on each side of the thorax the front and hind wings are held together with tiny hooklets on the leading edge of the hind wing that catch on the caudal edge of the front wing. In this way, the front and hind wings function as a unit in flight (Figure 3.6).

      The wings are powered by muscles within the thorax which act to compress or expand the shape of the thorax, and thus raise and lower the wings. Although the flight mechanism is relatively simple, the honey bee has great maneuverability, being able to hover and to fly forward, backward, and sideways.

      Deformed wings may be observed in hives affected by deformed wing virus, so it behooves the veterinarian to make note of the wing structure of any honey bees on a frame, as bees with this condition may be unable to fly.

Figure 3.6 Wing hooklets, greatly magnified.

      Source: Photo courtesy of Jamie Perkins.

      Legs

      Like all insects, honey bees have three pairs of legs (front, middle, and back), all attached to the thorax (left and right). There are

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