The La Brea Tar Pits in Los Angeles, California, are famous for the thousands of bones of saber-toothed cats, mammoths, and other outsized creatures that scientists have dug out of its oozy pools. But sometimes it’s the little things that count. In a paper published online today in PLOS ONE, researchers working at the site have now identified two beautifully preserved nests of the leafcutter bee (Megachile gentilis), so-called because the female insect constructs the nests out of leaf fragments glued together with saliva and leaf sap. And when they peered inside the nests using micro-CT scanning, they found equally well-preserved pupae of the insects (lower image and video). Comparison with modern pupae of this still extant species (upper image) confirmed the taxonomic identification, and also gave the team important information about the climate and environment at the pits during the period between about 35,000 and 40,000 years ago when the bees were buzzing around the area. Although the team could not identify the exact species of leaves the nests were made from, they were able to narrow them down to woody trees, shrubs, or vines, rather than herb plants, thus giving an indication of the local vegetation; and the climate at the time would probably have been mild, because modern leafcutter bees live in conditions that are rarely below freezing.

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