Anak Muda

Photograph courtesy J.G. Rozen, AMNH

What appears to be part of a spring wedding bouquet is actually a nest for a rare species of solitary bee, a new study says.

Called a "flower sandwich," the three-tiered arrangement consists of a thin layer of petals on the outside, then a layer of mud, and finally another layer of petals lining the inside of the chamber, according to study leader Jerome Rozen, a curator of invertebrate zoology at the American Museum of Natural History in New York.

At the core of the sandwich is the bee's larva, which feasts on nectar and pollen deposited inside the chamber by its parent before the egg is laid and the nest is sealed. (Related: "Bees Like It Hot: Pollinators Prefer Warm Flowers, Study Reveals.")

The colorful nesting behavior of the Osmia avosetta bees was discovered on the same day by teams in Turkey and Iran, where the insects are mostly found.

The teams jointly described the behavior in the February 2010 edition of the journal American Museum Novitates.
—John Roach

Each bee nest—like the three multihued samples above—has room for a single larva, noted the American Museum of Natural History's Rozen.

The Turkish and Iranian teams also noticed regional variations between the nests: Bees in Turkey—where Rozen was working—tend to pick yellow, pink, blue, and purple petals, while Iranian bees make their nests with just purple flowers. (See pictures of life in purple.)

"We don't quite understand what is going on" with their color selections, Rozen said. "It may be a genetic difference or a slight difference in the [bee] population"—or something else entirely.

He loves me; he loves me not? An Osmia tergestensis bee (pictured biting a petal from a flower) is another species that, like O. avosetta, builds its nests with flower petals.

In addition to O. avosetta and O. tergestensis, only two other bees species are known to use the flower-sandwich strategy, scientists say. However, other bee species will make their nests with a blended mixture of petals and mud—and some will actually chew up the petals.

In recent experiments, scientists teased apart the top of a flower-petal nest to reveal the chamber (pictured). The bee fills the hole with nectar and pollen before laying a single egg inside.

To close up the nest, the bee bends the inner layers of petals toward each other, spackles the petals with mud, and folds down the outer petals for a tight seal, according to the American Museum of Natural History's Rozen.

The petal and mud layers likely help to keep the larva's food—nectar and pollen—moist for about ten days, the American Museum of Natural History's Rozen said. Afterward the larva spins a cocoon and falls into a ten-month slumber, waiting for spring.

During the baby bee's long sleep, the "manufactured chamber that the bee larva is in dries out and becomes very hard. … The whole thing becomes nutlike," he added.

That hardiness protects the nest from predators such as ants and wasps, as well as from getting crushed under the weight of creatures that walk on top of the shallowly buried chambers.

Solitary bees generally live for about a year, but they are active for only about two months during spring and summer. The other ten months the larvae (above, a single larva in a petal nest) sleep underground, according to the American Museum of Natural History's Rozen.

"They don't last for very long," he said. "They very quickly do their nesting and then they die, and then the next generation is marching on its way."