What Are Bees

A major group of the order Hymenoptera is the Section Aculeata, i.e., Hymenoptera whose females have stings— modifications of the ovipositors of ancestral groups of Hymenoptera. The Aculeata include the wasps, ants, and bees. Bees are similar to one group ofwasps, the sphecoid wasps, but are quite unlike other Aculeata. Bees are usually more robust and hairy than wasps (see Pls. 3-15), but some bees (e.g., Hylaeus, Pl. 1; Nomada, Pl. 2) are slender, sparsely haired, and sometimes wasplike even in coloration. Bees differ from nearly all wasps in their dependence on pollen collected from flowers as a protein source to feed their larvae and probably also for ovarian development by egg-laying females. (An exception is a small clade of meliponine bees of the genus Trigona, which use carrion instead of pollen.) Unlike the sphecoid wasps, bees do not capture spiders or insects to provide food for their offspring. Thus nearly all bees are plant feeders; they have abandoned the ancestral carnivorous behavior of sphecoid wasp larvae. (Adult wasps, like bees, often visit flowers for nectar; adult sphecoid wasps do not collect or eat pollen.)

Bees and the sphecoid wasps together constitute the superfamily Apoidea (formerly called Sphecoidea, but see Michener, 1986a). The Apoidea as a whole can be recognized by a number of characters, of which two are the most conspicuous: (1) the posterior pronotal lobe is distinct but rather small, usually well separated from and below the tegula; and (2) the pronotum extends ventrally as a pair of processes, one on each side, that encircle or nearly encircle the thorax behind the front coxae. See Section 10 for explanations of morphological terms and Section 12 for more details about the Apoidea as a whole.

As indicated above, the Apoidea are divisible into two groups: the sphecoid (or apoid) wasps, or Spheciformes, and the bees, or Apiformes (Brothers, 1975). Older authors also used the term Anthophila for the bees and the name was resurrected by Engel (2005); Apiformes is a junior synonym of Anthophila. No priority rules govern such names. I prefer Apiformes because it contrasts well with Spheciformes and because the word itself makes its meaning immediately clear. Structural characters of bees that help to distinguish them from sphecoid wasps are (1) the presence of branched, often plumose, hairs, and (2) the hind basitarsi, which are broader than the succeeding tarsal segments. The proboscis is in general longer than that of most sphecoid wasps. The details, and other characteristics of bees, are explained in Section 12.

A conveniently visible character that easily distinguishes nearly all bees from most sphecoid wasps is the golden or silvery hairs on the lower face of most such wasps, causing the face to glitter in the light. Bees almost never exhibit this characteristic, because their facial hairs are duller, often erect, often plumose, or largely absent. This feature is especially useful in distinguishing small, wasplike bees such as Hylaeus from similar-looking sphe-coid wasps such as the Pemphredoninae.

The monophyletic Apiformes is believed to have arisen from the paraphyletic Spheciformes. Monophyletic is used here in the strict sense sometimes called Holo-phyletic. Such a group (1) arose from a single ancestor that would be considered a member of the group, and (2) includes all taxa derived from that ancestor. Groups termed Paraphyletic also arose from such an ancestor but do not include all of the derived taxa. Brief explanations of other terms used by systematists are appended to Section 12.

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