Insects have three distinct body regions or tagmata: the head, thorax, and abdomen. Insects in the order Hymenoptera, suborder Apocrita, to which bees belong, have their first abdominal segment fused to the thorax, as the propodeum, and the remainder of the abdomen (abdominal segments 2, 3, and so on) is narrowly connected to this fused region. Therefore, the terms mesosoma (thorax + first abdominal segment) and metasoma (remaining abdominal segments) are often used to describe these body regions (Michener 1944, 1974; Grimaldi and Engel 2005). Here, we use the terms head, thorax (including the propodeum), and abdomen, but make the clear distinction when referring specifically to the propodeum or metasomal segments (e.g., T1 represents the first metasomal tergum and S1 denotes the first metasomal sternum).
The figures below show basic bee morphology with emphasis on commonly used diagnostic traits (all illustrations by Morgan Christman). Other, more specific diagnostic traits, such as those to distinguish specific genera or species, are indicated in fact sheets and key images of each group.
Female and male bees are sexually dimorphic. In general, females can be identified by the presence of scopa (a region of dense branched hairs used to harvest pollen) on their hind legs (most bees), abdomen (Megachilidae), or sides of propodeum (Andrena). Males lack scopa, as they do not collect pollen to provision nests for young. Note that some female bees, however, store pollen in their crop and lack scopa, and cleptoparasitic bees have partially or completely reduced scopa.
Female bees have 6 exposed metasomal tergal segments, as well as a stinger (i.e., an ovipositor that has become modified for defense). Male bees usually have 7 exposed tergal segments, and no stinger. Note that the stinger is not always visible; female stingers may be retracted. Further, males sometimes have a mid-apical projection on T7 that can be confused for a stinger.
Female bees have 12 antennal segments (including the scape and pedicel), whereas male bees have 13 segments.
There are some exceptions to the characters listed above. For example, the tribe Meliponini, which are found in tropical and southern subtropical areas of the world (Michener 2007), contains stingless females. Further, in rare cases, bees can exhibit both male and female traits. Bees with this condition are either considered gynandromorphs or have been parasitized by Stylops, a minute parasitic insect that can cause androgyny in adult bees. (Images below all taken by Chelsey Ritner.)
The easiest way to recognize bee larvae is by looking at the associated nest (i.e., its architecture, organization, substrate used, and where it is made). Bee nest cells are provisioned with pollen, but the identification of a bee larva to family (or more specific classification) is challenging. Very few researchers have studied the larval forms of bees, so nearly all identification literature is based on adult morphology. Therefore, this tool is designed for identification of adult bees only. For information about larval identification, see Baker et al. (1985), McGinley (1987), Rozen (1973), Rozen and Kamel (2006), and Rozen et al. (2016).
Nests may be used to help identify bees to family or genus. We briefly summarize nests built or used by different families and genera under Biology and behavior and, when available, include photos of nest cells built by certain species and genera in the associated fact sheets.