Bees ofmany genera can be identified to genus at a glance, or at least very promptly, by a person familiar with the bees of the relevant region. This is possible in part because of the diverse body shapes of bees. I have indicated general body shape in the text by a series of terms such that with a single word a person who knows a few common genera of bees can get an idea of what bees of an otherwise unknown genus look like. These terms, following Michener, McGinley, and Danforth (1994), are listed below, arranged in a general way from slender and relatively hairless to robust and hairy. References to the colored plates, as well as to the habitus drawings and photographs, are offered so that the reader might gain a better idea of the meanings of these terms. The terms are subjective, however, and can be used only to give a general idea of body form and often hairiness. (Terms marked by asterisks apply primarily to megachilids and therefore indicate the large-headed megachilid body form.)
Hylaeiform. Body form of Hylaeus, also suggestive of a pemphredonine wasp. Slender, the hairs inconspicuous without magnification; scopa inconspicuous or absent (Pl. 1; Figs. 90-1, 90-10b).
Nomadiform. Body form of Nomada. Slender, wasplike, not noticeably hairy, often with yellow or red markings; scopa absent (Pl. 2; Figs. 93-2, 94-1, 102-2).
Epeoliform. Body form of Epeolus, Triepeolus, or Do-eringiella. Somewhat more robust than Nomada but nonetheless wasplike parasitic bees; scopa absent. Body often with areas of short, pale pubescence forming a conspicuous pattern (Pl. 2; Figs. 93-4, 95-1, 96-1, 97-1, 98-1, 100-1, 105-1).
Andreniform. Body form of Andrena, Halictus, or Colletes. Male often slender, its metasoma more parallel-sided than that of female (Pls. 3-5; Figs. 40-1, 49-1, 49-2, 58-3, 58-9, 59-4, 59-6, 60-1, 64-7).
*Heriadiform. See hoplitiform (Figs. 81-6, 81-7).
*Hoplitiform. Body form of Hoplitis (Alcidamea), Heriades, or more slender species of Megachile (Callomegachile). Similar to megachiliform but more slender, metasoma parallel-sided. The term heriadiform has been used for this body form, but implies greater slenderness (Pl. 6; Figs. 81-8, 84-9).
*Chalicodomiform. Between hoplitiform and megachiliform (Pls. 7, 8; Figs. 81-5, 82-9, 82-11, 84-15).
*Megachiliform. Body form of Megachile (Megachile) or Anthidium. Body heavy, head thick, meta-soma rather wide, not parallel-sided (Pls. 7, 8; Figs. 81-10, 82-15, 84-8).
Trigoniform. Body form of Trigona and its relatives, e.g., of the genus Partamona. Metasoma small and robust to slender and parallel-sided; body not conspicuously hairy, i.e., hairs short, and metasoma usually shiny (Pl. 9; Fig. 108-1).
Apiform. Body form of workers of Apis mellifera, i.e., more robust than andreniform and more slender than euceriform (Pls. 9, 10).
Euceriform. Body form of Eucera or Melissodes. Similar to anthophoriform but somewhat less robust (Pls. 11, 15; Figs. 111-1, 112-1, 112-2, 117-1, 117-2).
Anthophoriform. Body form of Bombus. Robust, head, thorax, and sometimes metasoma with abundant hair, thus enhancing the aspect of robustness (Pls. 10, 12, 13, 15; Figs. 88-1, 106-1). The term bombiform may be used especially for those with a hairy metasoma.
Bombiform. See Anthophoriform (Pl. 14; Figs. 1161, 116-7).
Many bees, of course, do not fall unequivocally into one or another of the above categories. For dry spec-imems, much depends on how full the crop was when the specimen was killed, how much the metasoma has telescoped in drying, and so forth. Nonetheless, these terms may be useful in suggesting the characteristic aspects of groups of bees. Some genera, such as Coelioxys because of its tapering conical metasoma, do not fall readily into any of the above categories.
At the outset, a question arises about the names for the three tagmata, or main parts of the body. Logically, they should be "head, thorax, and abdomen" or "prosoma, mesosoma, and metasoma." For simplicity I prefer the first series. But because the first true abdominal segment is incorporated into the thorax as the propodeum, the numbering of segments in the remainder of the abdomen should begin with 2 (as was done by Michener, 1944, 1954b). In bees, many taxonomically important structures are on one or another of the segments. But because of confusion as to an author's terminology, "first abdominal segment" could mean either the propodeum (if the reference is to be morphologically correct, as in Michener, 1944), or the segment next behind the propodeum, i.e., the first segment of the metasoma, as in most other works. To make it clear that I am following the customary system of numbering, I always speak of metasomal rather than abdominal terga and sterna. Thus the first metaso-mal segment is the segment behind the propodeal-meta-somal constriction. I use the names head, thorax (including the propodeum), and metasoma in order to combine familiar, unequivocal terms with a term that is not confusing for segmental numbering. Abbreviations such as T1 (first metasomal tergum), S1 (first metasomal sternum), and so forth, are regularly used to save space.
The word "gaster" has been recommended by some authors as an alternative to "metasoma." The problem is that, especially for taxa other than bees, such as wasps and ants, it is morphologically deceptive. It really refers to the enlarged or swollen part. For bees it would not be confusing, for it would be entirely equivalent to "metasoma," i.e., the first and following metasomal segments. For an ant or wasp with a one-segmented petiole, gaster com prises the second and following metasomal segments, and for an ant with a two-segmented petiole, the gaster is the third and following metasomal segments. Thus if one hopes for a uniform terminology throughout the Ac-uleata or the Hymenoptera, in which homologous structures have the same names, "gaster" is unsatisfactory, because a particular numbered gastral segment may be numbered differently in related taxa.
The sexes in bees are often quite different from one another, and in the keys the sexes are sometimes treated separately. Most males have 13 antennal segments or anten-nomeres, as they are often called, but there are only 12 in some Euryglossinae (some species of Euryglossina), some Ammobatini (Pasites, Melanempis, and Parammoba-todes), some Ammobatoidini (Holcopasites), some Bias-tini (some species of Biastes), some Halictini (some species of Thrinchostoma), and some Augochlorini (Chlerogas); only 11 or 12 in Systropha (Rophitinae); and
14 in Uromonia s. str. (Meganomiinae). Females have 12 antennal segments, although there are only 11 in some species of Euryglossina (Euryglossinae). Males usually have seven exposed metasomal terga; females have six. Sometimes the apical terga are retracted beneath the preapical ones, so that female Halictinae, for example, usually appear to have only five terga, and in some male bees, such as Protosmia, T7 can be seen only with difficulty, because it is largely or wholly retracted and must be dissected out if one wishes to examine it. Females have stings, and males have sclerotized genitalia, but both are usually retracted, and in some females the sting is rudimentary. The sting and associated structures are reduced and not (or weakly) functional in many Andrenidae; more reduced, not at all useful for stinging, in the Meliponini; and maximally reduced, compared to all other bees, in the Dioxyini. For sting reduction see Figure 27-1.
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