The next step was to determine how the native earthworms respond to the presence of moles. He built a small test box (20x25x19 cm) and filled it with 50 earthworms. The box had a tube in the side that allowed him to introduce a mole to the mix. As soon as a mole began tunneling into the test box, dozens of earthworms popped to the surface, wriggling at top speed with many even crawling over the top of the box.
"Eastern moles don't come to the surface when they are foraging, so fleeing to the surface provides the worms both immediate safety and the most efficient means for getting away from them," Catania says.
He repeated the experiments in two larger outdoor enclosures (1.2 square meters or 13 square yards) with similar results in this more natural setting. He did find one difference in the worms response to grunting and mole digging: When the worms surfaced in response to grunting, they headed every which way; when they surfaced in response to the sound of a mole digging, most of them began crawling away from the mole's position.
The biologist also used the small test box to explore another popular explanation for the worm grunting effect: That it imitates the vibrations caused by heavy rainfall, bringing the earthworms to the surface to keep from drowning. After placing 50 of the earthworms in the test box he put it under a sprinkler for an hour. The system simulated a heavy downpour that produces one inch of rain per minute. In five trials, a total of only three worms came to the surface. When the dirt in the box was totally saturated, he removed the earthworms and found that they appeared completely healthy.
"This made the rain hypothesis questionable," he says. But the more definitive test of rain w
|Contact: David F. Salisbury|