Spring means honey bees flitting from flower to flower. In California, this frantic insect activity that starts in late winter and continues through the summer is essential to growing foods like almonds, cherries, raspberries and apples. Bees move pollen, making it possible for plants to grow the fruit and seeds they need to reproduce.
But honey bees don’t just move pollen from plant to plant. They also keep a lot for themselves. They carry it around in neat little balls, one on each of their hind legs. Collecting, packing and making pollen into something they can eat is a tough, intricate job that’s essential to the colony’s well-being.
When honey bees don’t have access to pollen, they start depleting the nutrients in their body, said Mark Carroll, an entomologist at the U.S. Department of Agriculture’s Carl Hayden Bee Research Center in Tucson.
“And that’s when things get a little rough for bees,” he said, “because you’re using your reserves.”
While nectar from flowers — and the honey they make with it — provide bees with the energy they need to fly around, honey bees also need pollen to grow their colonies. Older female adult bees collect pollen and mix it with nectar or honey and a little saliva as they go along, then carry it back to the hive and deposit it in cells next to the developing baby bees, called larvae. This stored pollen, known as bee bread, is the colony’s main source of protein.
“You don’t have bees flying along snacking on pollen as they’re collecting it,” said Carroll. “This is the form of pollen that bees are eating.”
Young adult female bees distribute the stored pollen to the whole colony. They eat bee bread to make a liquid food similar to mammal’s milk that they feed to growing larvae and adult bees, including the queen. They also give little bits of bee bread to older larvae.
“It’s so important to have good protein,” said Gene Brandi, a beekeeper in Los Banos. “We’re always endeavoring to have them in places where they have forage.”
When the almond fields were in bloom in February and March, Brandi placed 3,000 hives in the orchards. With 1.3 million acres of almonds planted in California’s Central Valley, it’s the biggest honey bee pollination in the world, he said.
On a warm March morning, hives in white wooden boxes lined the road between rows of almond trees loaded with white flowers. Bees came and went. Almond pollen, which is light yellow, is nutritious and sought after by honey bees, said the USDA’s Carroll.
“The almond pollination event, it’s the time of the year that for most parts of the United States there’s really nothing else available,” Carroll said. “And in some ways, if beekeepers can work it out, this is a great jump for them to get their colonies going for the spring.”
Honey bees have been facing challenges for over a decade and the trend appears to continue this year. Brandi said that beekeepers around the country suffered “extremely high losses” this winter with some losing half of their colonies. He said that pesticides, poor nutrition and tiny mites that transmit diseases to bees are likely to blame.
When the almond pollination was done in mid-March, Brandi moved his hives to feed on pollen from sage. In the summer, they’ll forage for pollen in cotton and alfalfa fields. Brandi’s goal is to produce honey with different flavors.
Bees make honey with nectar they collect in the afternoon. They spend their mornings collecting pollen, and they’re well-equipped to do so, with three million hairs that help them trap the grains.
Honey bees even have hairs on their eyes, said Marguerite Matherne, a doctoral candidate in mechanical engineering at the Georgia Institute of Technology, who is looking at the process of pollen collection up close. She and her colleagues found that the spaces between the hairs on bees’ eyes are about the width of a pollen grain.
“What this does is it suspends these grains above the eye, so that the leg can grasp them more easily and move them out of the way faster,” said Matherne.
When a bee lands on a flower, it nibbles and licks off the pollen, which sticks to its head. It wipes the pollen off its eyes and antennae with a brush on each of its front legs, using them in tandem like windshield wipers. It also cleans the pollen off its mouth part, and as it does this, it mixes it with some saliva and a little nectar or honey that it carries around in a kind of stomach called a crop.
Then the bee uses brushes on its front, middle and hind legs to move the pollen, conveyor-belt style, front to middle to back.
“They’re transferring the pollen from one brush to another, between their legs,” said Matherne. “It’s kind of like running a comb through your own hair.”
As it flies from bloom to bloom, the bee combs the pollen very quickly and moves it into baskets on its hind legs called corbiculae (core-BICK-you-lee). Each basket is made up of a concave section of the hind leg, which is covered by longish hairs that bend over and around the pollen.
The bee bends its back legs at the joint to squish the pollen into a ball, using the nectar or honey it added earlier to glue the pollen grains to each other.
“That way it’s wadded up, and it’s a lot easier to have that actually attached to their leg,” said Carroll.
Matherne found that a bee can fit as many as 160,000 pollen grains in each pollen ball or pellet. By the time a worker bee gets back to the hive with its haul, it is carrying as much as one-third its weight. The bee does this trip up to 12 times a day, said Carroll, its wings becoming ragged from the effort.
Back at the hive, bees deposit their pollen pellets close to the cells where bee larvae are growing. Another bee might come along and add some more honey to the pollen, and then the bee bread is essentially ready to eat. Scientists had believed that bees left the pollen to ferment for a few days. But Carroll and colleagues found that bees prefer their pollen fresh.
“Pollen that was less than a few days old was preferred over pollen that was seven to eight days old and beyond,” he said.
After a few weeks, the constant foraging trips take a toll and the bees die.
“It’s a paradox,” said Carroll. “At the time of the year when there’s most food available out in the landscape from flowers, that’s when they have the shortest lives because they’re just so busy.”
Get the best of KQED’s science coverage in your inbox weekly.