The 100-million-year extensive fossil record of bee brood nests and cells in sedimentary deposits, or paleosols, is usually devoid of the presence of their producers. Paleontologists have now discovered hundreds of long-horned bees (Eucerini) preserved in their brood cells in paleosols of southwest Portugal.
The 3,000-year-old long-horned bee. Image credit: Andrea Baucon.
The long-horned bees are members of the highly diverse tribe Eucerini within the family Apidae, with over 32 genera worldwide.
All known species are solitary, though many nest in large aggregations, and large aggregations of males, are found occasionally.
“With a fossil record of 100 million years of nests and hives attributed to the bee family, the truth is that the fossilization of its user is practically non-existent,” said Dr. Andrea Baucon, a paleontologist at the University of Siena.
At Carreira Brava, one of the four paleontological sites studied by Dr. Baucon and colleagues, long-horned bees of the genus Eucera ready to abandon their cells were found in an exceptional state of preservation inside the sealed brood chambers.
The chambers also preserved the inner cell membrane and remains of the monospecific Brassicaceae-type pollen.
“The degree of preservation of these bees is so exceptional that we were able to identify not only the anatomical details that determine the type of bee, but also its sex and even the supply of monofloral pollen left by the mother when she built the cocoon,” said Dr. Carlos Neto de Carvalho, a researcher at the University of Lisbon and Geopark Naturtejo, a UNESCO Global Geopark.
“Our project that led to this discovery identified four paleontological sites with a high density of bee cocoon fossils, reaching thousands in a square measuring one meter on a side.”
“These sites were found between Vila Nova de Milfontes and Odeceixe, on the coast of Odemira, a municipality that gave strong support to the execution of this scientific study, allowing its dating by carbon-14.”
Bees are important pollinators, whose populations have suffered a significant decrease due to human activities and which has been associated with climate change.
Understanding the ecological reasons that led to mummification of long-horned bees in Portugal nearly 3,000 years ago could help to understand and establish resilience strategies to climate change.
“Although the cause of mass mortality remains a mystery, oxygen depletion due to sudden flooding of the nesting substrate and consequent or overnight temperature drop, just before emergence, are plausible causes,” the authors said.
“The anaerobic conditions and later rapid carbonate diagenetic lithification are the likely causes of the preservation of the bees and the inner cell organic membrane.”
“The favorable climate conditions for the development of successive, dense ichnofabrics from an omission suite dominated by bee brood cells may be the result of slightly colder and higher-precipitation winters during the Neoglacial interval.”
Paleontologists working along the coast near Odemira, Portugal, have discovered the remains of hundreds of young adult bees mummified inside their cocoons.
Dating back to some 2,975 years ago, when Pharaoh Siamun reigned in Lower Egypt, the insects belong to the genus Eucera, which can still be seen buzzing around Portugal today.
Unlike Pharaoh Siamun, whose mummy is thought to have completely decayed, the bees are exceptionally well-preserved, recording even their smallest anatomical details.
This is “extremely rare”, the researchers noted, as the bodies of insects normally decompose rapidly thanks to largely being made of the organic compound chitin.
In fact, explained paleontologist Andrea Baucon of Italy’s University of Siena, despite “a fossil record of 100 million years of nests and hives attributed to the bee family, the truth is that the fossilization of their users is practically non-existent.”