isplay sites in the forest understory, where matings are known to take place. Although the accumulated volatiles have long been believed to serve as a signal to females, female attraction to male odors has never been demonstrated in behavioral experiments. The behavior of volatile collection is essentially unique in the animal kingdom. Single synthetic compounds are commonly used as bait to attract and collect males for study, and include many familiar flavorings and odors considered appealing to humans (e.g., methyl salicylate, eugenol, cineole, benzyl acetate, methyl benzoate, methyl cinnamate), and others which are not (e.g., skatole).
Neotropical orchids themselves often exhibit elaborate adaptations involving highly specific placement of pollen packets (pollinia) on the bodies of the male orchid bees; the specificity of their placement ensures that cross-pollination only occurs between orchids of the same species. Different orchid bee males are attracted to different chemicals, so there is also some specificity regarding which orchid bees visit which types of orchid. The early description of this pollination system was by Charles Darwin, though at the time, he believed the bees were females. Not all orchids utilize euglossines as pollen vectors, of course; among the other types of insects exploited are other types of bees, wasps, flies, ants, and moths.
Digger Bees. The Anthophorini is a large tribe in the family Apidae, with over 750 species worldwide that were previously classified in the family Anthophoridae; the vast majority of species are in the genera Amegilla and Anthophora. All species are solitary, though many nest in large aggregations. Nearly all species make nests in the soil, either in banks or in flat ground; the larvae develop in cells with waterproof linings and do not spin cocoons. Species in this tribe are often referred to as "digger bees", though this common name is sometimes applied to members of the tribe Centridini, as well (Figure 48).
Digger Bee, Image Courtesy of entomart.
The characters used to define this group are subtle, but they are nonetheless fairly recognizable; they are generally large (up to 3 cm), very robust, hairy bees, with visibly protruding faces, and the apical portion of the wings are studded with microscopic papillae. The abdomen is often banded, and in many Old World species of Amegilla these bands are metallic blue. The wings often appear disproportionately short compared to other bees, and their "buzz" is often a high-pitched whine, as they hover and feed on flowers. Males commonly have pale white or yellow facial markings, and/or peculiarly modified leg armature and hairs.
Attracting Digger Bees. Some digger bees nest in cracks or cavities in soft sandstone and dry exposed soil embankments. Some of these species will excavate tunnels in cliff sides by wetting the hard soil surface with water or nectar to soften it.
To attract these species, adobe bricks can serve as the equivalent of a wooden nest block. Such bricks can sometimes be purchased, in which case you can increase their attractiveness to bees by drilling nesting holes following the size recommendations listed above for wood blocks.
Adobe blocks can also be easily made where clay soils are common. To create one, half-fill a large bucket with clay soil, and then fill the bucket with water. Stir the mixture together to create muddy slurry and allow it to settle. Remove any sticks or debris floating on the surface and slowly pour off most of the water. Finally, pour the remaining sediment into a mold (such as a wooden box or small Styrofoam cooler), and allow it to dry for several days or weeks. Before it completely dries, you can make several 1-inch indentations, using the diameter guidelines above, to make it more attractive to bees.
Mount the brick, either singularly or in a stack. Adobe will not hold up well in wet climates and many need sheltering from rain. You might want to supply a shallow water source near your bricks to help bees excavate their nests.
Halictidae-Halictid Bees. This is a cosmopolitan f