The combs inside a hornet's nest are precise, intricate, and somehow assembled in pitch-black. Now, researchers have found that the insects may have a special tool in their kit to accomplish this feat of engineering: tiny crystals that may act like miniature spirit levels.
Hymenopterans--such as bees, wasps, and hornets--build surprisingly straight layers of cells within their nest combs. "It is an amazing thing, as the inside of the comb is in total darkness," says Jacob Ishay, a physiologist at Tel Aviv University. Previous experiments had shown that the insects take their cues from gravity; in a centrifuge, for instance, they build combs oriented toward the resultant gravitational force. To tease out gravity's role, Ishay's hornets have even boldly gone where no hornet has gone before: In 1992, 180 of them were sent aboard the space shuttle Endeavor to see if microgravity would scupper the orientation and integrity of combs. (Unfortunately, the experiment failed because most of the hornets died.)
Now another group of researchers headed by Ishay thinks they know how hornets can be so crafty. The team used an electron microscope to scan the hexagonal brood-rearing cells of the Oriental hornet (Vespa orientalis). In the 7 June issue of Nature, they report that a tiny crystal--no more than 0.1 millimeter in diameter--is glued to the domed roof of each cell. Diffractional analysis showed that the crystals are similar in composition to a titanium-containing mineral called ilmenite. Ishay believes that the crystal acts "like a surveyor's spirit level," guiding the hornets as they build, but it's unclear how exactly. The crystals are magnetic, but Ishay believes it's their weight that holds the secret. When the hornets tap the hive surface with their feet, "the crystal does not dance in the same way as the rest of the comb," enabling the insects to glean information about the orientation of their nest, he says.
The findings don't surprise David Liskowsky, acting director of NASA's Fundamental Space Biology division in Washington, D.C. "Gravity is a pervasive force on the planet and nature uses it to guide growth in many systems," says Liskowsky. "The most interesting and intriguing point," he adds, "is the possibility that the insects may secrete these crystals themselves," rather than collect them. Because both titanium and iron are present in the hornets' body, that's possible, Ishay says.