After a rain, large numbers of worms flock across strange, exotic landscapes, like driveways, sidewalks, and roads. Are they looking for adventure? For romance? Today, A Moment of Science looks at the reasons behind the Great Worm Odyssey.

Earthworms usually stay in the soil because they are not equipped to travel in the open air. They must remain moist at all times because they breathe through their skin, and it will not allow oxygen through if it is dry. Also, they cannot stand bright light. Only at night, when the sky is dark and the air is moist after a rainfall, can worms leave the soil and explore the world.

The reasons behind the worm odyssey are still unclear: some scientists believe that worms are looking for mates and others claim that the rain brings irritating chemicals into their burrows. In either case, scientists agree that worms are not trying to escape drowning, as is often supposed. Worms can absorb enough oxygen from water to survive a day or so in the wet ground. Perhaps, like mountain climbers, they explore simply because they can.