Emmett Glass noticed something unusual recently when his dust mites escaped from their petri dish. Instead of straying in all directions, the .3-millimeter-long creatures clumped together on the laboratory workbench. Glass, an entomologist at Ohio State, suspected that the mites were trying to conserve water. For years researchers have wondered how dust mites stay moist. In labs, individual mites dehydrate and die when the humidity drops below 50 percent. So how could the allergy-causing pests hang on in homes when moisture falls below fatal levels? Glass believes that the huddles help the mites survive. To test his theory, he removed some mites from their clumps and lowered the humidity levels. He then weighed them to see how much water they retained. Those in clusters lost about half the water of the isolated mites. Glass believes he knows how the mites survive. "Dust mites have glands packed with salt on the sides of their head," he says, "that suck water molecules from the air and siphon it into their mouths. When the mites cluster, these glands absorb and recycle excess water excreted by other mites." Glass suspects mites use chemical signals called pheromones to communicate the need to huddle, and he hopes to work out the chemical makeup of the pheromones. "Our ultimate goal," he says, "is to figure out ways to eliminate the pests."