Bee Anatomy

     The head of the bee has some structures that are important in identification besides being the centre of a lot of sensory collecting. The vertex is the top of the head and this region has three ocelli, which are “simple eyes”, often considered to detect light, but not producing an actual image.(see Figure 8)

Figure 8. Bee head showing the three ocelli, facial frons, facial fovea, compound eyes and antennae.

Below the ocelli is an area called the frons which is the “forehead” of the bee. Either side of this are the compound eyes which are really made up of many hexagonal shaped facets, each with its own connection to the optic nerve. These multi-faceted eyes collectively produce good vision, not as good as say our eyes, but the bee eye is much lighter in weight which is important for a flying insect. Bee vision is shifted to the ultraviolet (UV) level more than our vision, enabling bees to see ultraviolet patterns in their world, mainly used to detect UV patterns in flowers. Polarized light is another quality that bee vision is superior in, which enables bees to see essentially invisible patterns through cloud cover, especially the sun since bees orient their world around the position of the sun. The facets on the compound eyes also have small hairs on them for wind current detection. Bees can detect the wind changes and the effect wind has on the eye hairs, and instantly the bees can alter their steerage in the air in order to keep on their intended course. Some species of bees have males equipped with larger compound eyes, useful in detecting females to mate with. In some bees, just between the frons and the compound eyes, are areas of depression called the fovea. (see Figure 8) They are often used in identification and can be hidden by a dense growth of hairs, or exposed and obvious. They are better developed in females.               

Fig. 9. Antennae of female vs. male bee. Shorter female on left, longer male on right.

            Below the frons, are the connection points for the antennae, called the antennal sockets. The paired antennae are highly sensitive organs made up of 12 segments in the female, and 13 segments in the male, and used in smelling, hearing, feeling and tasting.(see Figure 9) Each antenna consists of the scape, the pedicel and then the 10 or 11 segmented flagellum. In the male, which has one more section in the flagellum, each segmented section can also be longer giving them an appearance of having longer antennae overall. Just below each antenna are one or two subantennal suture lines. It is important for us to know about these for identification purposes later. Since it is the males that are seeking out the females to mate with, it makes sense that they will have an advantage in the sensory department for picking up important olfactory chemicals emitted by the females, and larger compound eyes to see females, sometimes from far away.

            Below the antennae, and where the subantennal sutures terminate, is the clypeus, positioned where we would consider the “nose” of the bee. In some bees, this can be bare and contrastingly coloured, or covered with a thick mat of hair. Immediately below the clypeus are the mouthparts, made up of the upper lip – the labrum, the two mandible “jaws” just below and on either side, and then the lower lip – the labium. The tongue or glossa, is attached between the labrum and labium but is often folded underneath the head and can't be viewed unless the bee has it protruding.

Figure 10. Tongues of bees showing the short, trowel-like tongue of Colletes, and the longer, filamentous tongue of Anthophora on the right and in the middle (side view).

 Tongues vary greatly in different bee species and are used not only in the identification of bee families, but also fit the design of flower nectaries that the bees visit. (see Figure 10) The bee's tongue is essentially a tubular hairy rod with a sponge-like tip that absorbs moist liquids such as nectar or water, and the bee sucks the fluid through the tube into the mouth. However, as we will see later, some bees have very flat and broad tongues not suited for deep extractions of nectar inside flowers, but for surface feeding. These bees also use their tongues like a trowel when constructing their nest.

Fig. 11. Side view of typical bee with wings removed. This is a female as she has 6 tergal and sternal segments as well as a stinger. Male bees have 7 tergal and sternal segments and no stinger.

 The head is attached to the thorax at a relatively small joint to allow for flexibility. (see Figure 11) The first exoskeletal plate on the thorax is the pronotum extending forward to the attachment area of the head, behind the protection of the head which appears to cover it, much like a lampshade covering a lightbulb of a desk lamp. Immediately aft of the pronotum, when going along the top of the thorax crown, in order, are the scutum, scutellum, metanotum and propodeum. When going aft directly along the sides, are the episternum and the metepisternum. So, between these various plates, fit the tegula and the axilla where the fore wing and hind wing attach. The legs are attached at points along the lower sides of the thorax, at trunk-like bases called the coxae. The foreward leg coxa is directly below the pronotum, the mid-leg coxa below the episternum, and the hind leg coxa below the joint of the metepisternum and propodeum.

Figure 12. Top view of a typical bee.

Figure 13. Strigilis in front leg of some bee species which is used to clean the antennae.

The six legs are divided into three positions along the thorax, and all are different as they play unique functions in bee activity. (see Figure 11) However, the fore leg, midleg and the hind leg all share the common, basic components, that being the trochanter, femur, tibia, basitarsus, three tarsal (tarsus) segments and finally ending in the claw. But there are some important differences in leg components not only between different species, but also between the sexes. In some bees, specifically certain ground-nesting genera, the hind leg can have an additional component attached between the femur and the tibia called the basitibial plate, used to grip the sides of the tunnel as the bees scoot through their underground channels, sort of like logger's spurs for climbing trees. Some species have a sharp protrusion at the beginning or end of the tibia which is termed the tibial spine or tibial spur(s)*. (*some species have two spurs per leg). The tibial spur on the fore leg tibia of some bees, in conjunction with a concave pocket in the bsitarsus, form what is called the strigilis used to wipe the antennae through for cleaning.(see Figure 13) Also used for cleaning, but in this case to clean the wings, is an area on the inner surface of the tibia of the hind leg that has a patch of hairs that are of uniform length and are blunt. These hairs are called keirotrichia but not all bees have these. In some species, the females instead have long hairs in this spot, and are used in storing and carrying pollen in conjunction with the scopa – a section of the basitarsi with long hairs for collecting and carrying pollen.(see Figure 13) The scopae may also include the ventral surface of the abdomen in some species of bees. Bees that don’t have scopae may instead have another pollen carrying item called the corbicula, which is on the outer surface of the hind leg tibia. This is a largely hairless area, sometimes flat or concave, surrounded by a fringe of hairs. The female bees that don’t have scopae or corbicula, do not store or carry pollen at all on their body and may either ingest it instead as in Hylaeus, or don’t provide pollen since they are species of bees that are socialparasites or cleptoparasites. Another anatomical feature that is useful in identification of some bee species, is the presence, or lack of the arolium. This is a pad or flap that extends at the very end of the tarsal segments, and found between the tarsal claws. Bees with arolia (pl.) exhibit different shapes and sizes depending upon species.

Figure 14. Wings of the bee. Hind wing (top), hind wing (bottom) with most of the main wing veins and cell components.

            Bees have two pairs of wings consisting of the fore wings and hind wings. (see Figure XX) They are attached at bases on upper sides of the thorax; the fore wings connected to the base under the tegula and the hind wing below the axilla. Both wings are made up of their own respective components, but they both have a strong network of veins which divide the intervening clear, hyaline portions into cells. These veins and cells have been categorized and named by entomologist and are different in various species of bees. They are rather different in terminology but very useful in identification so some basic terminology should be grasped by those interested in bee identification.

            In the fore wing, the forward leading edge has a thickened vein called the costa (c) with the vein immediately behind that called the radius (R). Where the radius ends, part way along, a portion between it and the costa, there is a darkened patch of varying size in different species called the stigma. The next large vein that departs posteriorally or backwards off the radius is the basal vein (M). The basal vein branches off towards the end of the wing and parallels the wing margin and this is the anterior radius vein (R1). At the stigma, the radius branches into the radial sector (Rs). The radial sector also branches just prior to the stigma and between it and the other radial sector vein after the stigma, there is a series of cross veins called the subgmarginal crossveins (1r-m, 2r-m, and 2nd abscissa of Rs).

            Paralleling the basal vein and proceeding outwards or distally, are the submarginal crossveins (1m-cu and 2m-cu). The vein immediately below the outer submarginal crossvein is the second recurrent vein (2m-cu).

            All these veins that intersect, enclose spaces which create cells that are also important identifications for bee species. The large cell at the leading edge of the wing, just distally of the stigma is the marginal cell. The two or three cells immediately posterior of this and the stigma, are the submarginal cells.

            The hind wing has some unique features, plus their own version of the same components as the fore wing. With four wings, it is more efficient to lock the fore wing and hind wing together to form one large flapping plane when flying.

Figure 15. Hind wing of bee showing hamuli on leading edge which hooks onto the trailing edge of the fore wing, connecting the wings together in one larger plane for a more efficient flight.

This is achieved by “clipping” the wings together with a series of hooks found along the leading edge of the hind wing mid-section called hamuli, that catch on to the trailing edge of the fore wing. With the wings formed into one plane, the bee uses its large internal muscles within the thorax to constrict and expand the entire thorax to beat much faster than if the muscles were directly attached to each wing as in dragonflies. Dragonflies have superior control in the air with four independently controlled wings but for the size of wings versus the overall weight of the body that a bee has, bees make efficient use of these small wings for speed but aren't as adept at feats of acrobatic flight like the dragonflies have.

            Two important and different cells to make note of in the hind wing of bees, are at the posterior edge of the wing. These are the large vanal lobe and varying sized jugal lobe, often used in bee species identification. (see Figure XX) Overall, the hind wing is a smaller wing and has reduced wing veins and consequently, fewer cells.

Figure 16. Abdomen of the bee

The abdomen is sometimes referred to as the metasoma, but here, the ubiquitous term, abdomen, will be used.(see Figure 16) It is made up of segments and each segment has a top section, tergum, and a bottom section, sternum. Females have six segments, whereas males have seven, but sometimes each segment is difficult to see as they can be completely hidden from view. In actual fact, the last segment of the thorax which is the propodeum, is really the first segment of the abdomen but the customary way of terminology is what will be used here and retain the propodeum with the thorax. The abdomen houses various vital organs internally, including the heart, glands used in nest construction or communication, and sexual reproduction. In the female, they have a stinger which is also part of the egg-laying apparatus which is called the ovipositor. There are organs to support the use of either egg-laying or venom for stinging. Some bee species have a much reduced potency to their sting, or lack the ability to sting at all. There are true stingless bees in the world, but these taxonomic groups do not exist here in our region. The introduced honey bee is the only bee here in our area which has a barbed stinger or lancet and when this species of bee stings us, the stinger is unable to retract and so it is evicerated along with the venom sac, and continues pumping separate from the bee. The bee eventually dies. Our native bees can sting repeatedly but the intensity of the venom varies in level of pain to the individual being stung but is less than the honey bee however.

            The terga and sterna, are numbered sequentially anteriorally to posterially and labelled T1 and S1 etc. On some bees, a small protrusion on the dorsal surface of the terga plates can be seen between T5 and T6 on females and between T6 and T7 on males. This is called the pygidial plate and sometimes are referred to for identification purposes. The pygidial plate is used as an application tool for secretions that are exuded in the abdomen, for lining the nest cells in some andrenid and halictid bees.

Figure 17. Abdomen of bee showing pygidial plate near terminal end.