This is Panurgus banksianus, the large shaggy bee. It lives alone, burrowed into sandy grasslands across Europe. It prefers to feed on yellow-flowered members of the aster family.
The large shaggy bee also has a very large brain.
Just like mammals or birds, insect species of the same size may have different endowments inside their heads. Researchers have discovered some factors linked to brain size in back-boned animals.
But in insects, the drivers of brain size have been more of a mystery. In a study published Wednesday in Proceedings of the Royal Society B, scientists scrutinized hundreds of bee brains for patterns. Bees with specialized diets seem to have larger brains, while social behavior appears unrelated to brain size. That means when it comes to insects, the rules that have guided brain evolution in other animals may not apply.
“Most bee brains are smaller than a grain of rice,” said Elizabeth Tibbetts, an evolutionary biologist at the University of Michigan who was not involved in the research. But, she said, “Bees manage surprisingly complex behavior with tiny brains,” making the evolution of bee brains an especially interesting subject.
Ferran Sayol, an evolutionary biologist at University College London, and his co-authors studied those tiny brains from 395 female bees belonging to 93 species from across the United States, Spain and the Netherlands. Researchers beheaded each insect and used forceps to remove its brain, a curled structure that’s widest in the center. “It reminds me a little bit of a croissant,” Dr. Sayol said.
One pattern that emerged was a connection between brain size and how long each bee generation lasted. Bees that only go through one generation each year have larger brains, relative to their body size, than bees with multiple generations a year.
This is similar to what research has shown in birds. “A big brain takes a lot of time and energy to grow,” Dr. Sayol said. “The more time they have to develop, the bigger the brain.”
Looking at the bees’ diets revealed a more surprising tendency.
In birds, “we know that species that have a broader diet tend to have bigger brains,” Dr. Sayol said. The challenge of finding and consuming a wide variety of foods may demand a large brain. However, Dr. Sayol said, “We found the opposite in bees.” The biggest brains were in dietary specialists, such as the aster-loving large shaggy bee.
Dr. Sayol speculated that a broad diet might be less of a challenge for bees than it is for birds, because all bees feed on flowers. A bee with a broad diet can fly into a field and drink the first nectar it finds. But a bee with a specialized diet may have to spot its preferred bloom, with its specific color and fragrance, among a whole field of similar flowers — a task that might require more brain.
Larger brains have also been linked to social behavior in primates and other mammals. But scientists found no connection between brain size and whether a bee lived in hives like honeybees or was a loner like our big-brained aster-eater.
This might not be such a surprise, Dr. Sayol said. “The sociality of bees is very different from what we understand as sociality in vertebrates.”
In back-boned animals, being social means having to keep track of many other individuals. But although a beehive is large and complex, each bee within it has a specialized job, such as foraging for nectar and pollen. This form of social living may not demand a large brain, Dr. Sayol said.
Other research in wasps has supported this idea, Dr. Tibbetts said, and even shown that the most social bugs are the least brainy. “Highly social species have smaller brains because each individual is more like a cell in the body of the hive,” she said.
Dr. Tibbetts said that even for vertebrates, whether bigger-brained animals are smarter is a topic of wide debate. Scientists know even less about what it means for an insect to have a large or small brain, Dr. Tibbetts said, and the new research begins to answer that question.
“This is a fantastic study,” she said.
Dr. Sayol is returning to birds, his usual area of research, but he said he’s gained a new appreciation for bees and their brains. The study illustrates that no matter how much scientists think they know about brain evolution from studying vertebrates, those rules may not apply to the insect world.
“We have to be careful,” Dr. Sayol said. “Some of the hypotheses, maybe they are not as universal as we think.”