Bee Fossils Shed Light On The Environment In The Late Pleistocene

Top: Harold Ikerd/USDA-ARS Pollinating Insect Research Unit at Utah State University, modern pupae of the leafcutter bee. Bottom: Justin Hall/Dinosaur Institute, Natural History Museum of LA County, CT scan of preserved pupae.

Scientists have identified two incredibly well preserved nests containing equally well preserved pupae of the leafcutter bee from the La Brea Tar Pits in Los Angeles. The results, which have been published in the journal PLOS ONE, are helping to divulge information on the climate and environment in this area around 40,000 years ago.

Rancho La Brea, or the La Brea Tar Pits, is famous for the large number of diverse fossils that have been pulled out of these oozing pools. From animals such as saber-toothed cats and mammoths to extinct Ice Age plants, some 3.5 million specimens representing over 600 different species of plants and animals have been collected here. Less attention has been paid to its plethora of insects, but these can in fact serve as valuable environmental indicators since they are fairly restricted by climate and have short life cycles.

Hoping to learn more about the local habitat and climate of Rancho La Brea towards the end of the last Ice Age, scientists investigated two fossil bee nest cells collected here. They used micro-CT scans to examine the cells, which led them to the discovery that they contained exceptionally well preserved pupae as well. Further investigation of the features of both the bees and the nest cells led the scientists to the conclusion that they were likely leafcutter bees (M. gentilis), which still exist today.

Leafcutter bees use pieces of leaves when building nests, which they usually form under the bark of dead trees or in burrows either dug by the bees or other animals. The females use sharp mandibles to cut the leaves which are then used to line nest cavities.

The scientists were able to use the leafcutter specimens to shed light on the environment in southern California during the Late Pleistocene. They suggested that the environment the bees were living in was probably mild, and although they couldn’t formally identify the material used to build the nests they found that it was more likely to be from woody trees and shrubs as oppose to herb plants.

According to Dr. John Harris of the Page Museum, the scientists are hoping to use information from fossils such as these to understand how animals responded to the climatic change experienced at the end of the Ice Age. “It affords an evolutionary perspective to ongoing climate change,” he added. 

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