The following is an excerpt from Endless Forms: The Secret World of Wasps, by Seirian Sumner.

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Endless Forms: The Secret World of Wasps

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124 million years ago, all the bees were wasps. Then one day a wasp forgot how to hunt and developed a taste for pollen, and bees were born. Some of them even evolved special saddlebags on their back legs which helped them carry pollen back to their nests. Bees have become guardians of global ecosystems as pollinators, and a privileged few are honored friends of humans as providers of honey, wax and other useful products, but the truth is that in evolutionary terms, there is nothing especially unique about bees: they are simply a specialized, vegetarian version of the largest group of wasps—the crabronids.

The bee fossil record remains scrappy and sparse compared to that of ants. Most of the bee fossils are solitary species, while most of the fossil specimens are social bee workers from species that lived in damp forests and fed on resins (like stingless bees). Since social bees didn’t evolve until 60 million years after the first solitary bee, the vast majority of bee fossils are not especially useful for revealing how wasps became bees. Despite this, we have two fossilized contenders for the star role as the wasp-bee—a transitional state that links wasps to bees—and they come from Burmese amber that formed in tropical forests 100 million years ago. Fossils of Melittosphex burmensis and Discoscapa apicula both sport a mixture of wasp-like and bee-like features, suggesting that they could be missing links between crabronid wasps and bees. To the trained taxonomists’ eyes, however, these two insects are so different from each other that they belong in different biological families. Moreover, there are no living representatives of their families, making them new to science.

The closest living wasp relative to bees is most certainly a wasp from the Crabronidae family, probably something like the aphid wasp, such as Psenulus—a global genus of around 160 species. As the name suggests, these solitary wasps hunt aphids, which they paralyze to provide as living prey to their larvae. Another candidate for the closest living relatives to bees are the Ammoplanidae, tiny wasps, barely 2–4 millimeters in length. These are compelling contenders, as the wasp-bee fossils (like Melittosphex burmensis) that have been found are also extremely small (around 3 millimeters). Since the flowers of the early Cretaceous would have been very small, it would make sense if the first bees were sized to fit. Intriguingly, Ammoplanidae hunt tiny pollen-eating insects called thrips. In the late 1960s, the Russian entomologist Sergei Ivanovich Malyshev suggested that wasps which hunted flower-visiting insects could have experienced the conditions needed for a diet hop from hunting meat to pollen-foraging. 50 years later, his theory finally appears to have received some evidence.

These thrip-hunters would already have had a sensory system well tuned to locating flowers: a perfect starter toolkit for the proto-bee. It is easy to imagine these wasps carrying home a few pollen grains as a side-dish to the crunchy thrips. All that would have been needed was some genetic mutation that enabled the brood to make nutritional use of pollen, and the evolutionary seeds for the original bee would have been sown.

In 2019, another piece of 100-million-year-old Burmese amber provided definitive evidence of a pollinating wasp: it revealed a stinging wasp with plumes of pollen wafting from its mouth, and a pollen ball stored inside its body—direct evidence that this was a pollen-feeder. The wasp looked unlike anything seen before, with somewhat ancestral or primitive features, and it didn’t fit into any of the main lineages of modern stinging wasps. The researchers called it Prosphex anthophilos, forming a new genus Prosphex (pro– meaning ‘first’/‘before’ and –sphex meaning ‘wasp’).

The scientists proclaimed it to be an unprecedented discovery because it was the earliest direct evidence of an insect pollinating a flowering plant. Given the beautiful story of co-evolution between flowering plants and their insect pollinators, this was indeed a landmark discovery. But equally important is that it provided evidence of wasps evolving pollen-foraging at least as early as the origin of bees and around the time that flowering plants started diversifying. This is indisputable direct evidence that dependence on pollen can evolve from a predatory ancestor.

Perhaps we shouldn’t be so surprised that stinging wasps gave rise to some of the pollinating giants. Wasps have many traits and behaviors that could have been pre-adaptations for becoming effective pollinators. They are aeronautical champions with good memories: their strong, coordinated flight and ability to learn landmarks (from building and provisioning many new nests over many months) would have provided a physical and cognitive toolkit for finding good pollen sources and returning to the same food source until it was depleted. And their sting: what better way to protect yourself when foraging on exposed flowers? It is small wonder that so many hundreds of flower-visiting flies, beetles and moths have mimicked the wasp’s signature yellow and black outfit. Equipped with speed, intelligence and defense, the wasp that became a bee was well set up for a lifetime’s devotion to flowers.

From Endless Forms: The Secret World of Wasps by Seirian Sumner. Copyright 2022 by Seirian Sumner. Excerpted by permission of Harper, an imprint of HarperCollins Publishers.