Cavity-nesting bees are enigmatic because they are difficult to observe in the wild, hence trap-nests (man-made cavities) provide the means by which these bees may be studied. Trap-nests is an efficient methodology to study these bees and are common worldwide. These traps have been used for a variety of reasons, including inventories, to examine pollen load, to study habitat disturbance, and bee conservation. However Neotropical trap-nesting bees’ taxonomy and biology are still poorly known and here we provide a review about these subjects. We searched for trap-nest bee studies in the Neotropical Region using Google Scholar and ISI Web of Science at any time in the past to December 2017. We found 109 independent studies, most of which were from Brazil (87 studies), followed by Argentina (10 studies), and other countries had fewer than five studies each. A total of 140 species, 24 genera, 10 tribes and three subfamilies were reported in trap-nests. Nest architecture was described for only 49 species. Taxonomy is only well-known for 14 genera, somewhat known for seven and is essentially unavailable for three genera. Construction material, closing plug and cell shape are similar among species in the same tribes and genera. Vestibular and intercalary cells, and the preliminary plug are variable, even at the specific level. Apinae is the most studied group with available data for all genera recorded in trap-nests. Colletinae is the least-studied group and nothing is known for their nesting biology. Megachilinae is intermediate, with some studies of taxonomy and nesting. We suggest that further trap-nest studies should provide more detailed information on nest architecture and construction materials, including explicit mention of structures that are absent. All Neotropical bees need more taxonomic studies, but some, such as Hylaeus and Megachile, require more attention since Hylaeus is essentially unknown and Megachile is very common on trap-nests.
