Tarantula "migration" is not a migration, it is simply a part of the mating process of tarantulas. Male tarantulas must actively seek out females, which stay in burrows underground. As the males travel over great distances at times, humans who see them sometimes assume they are migrating.
Female tarantulas can lay anywhere from 500 to 1,000 eggs from one mating session. Males make a quick exit after mating, because females sometimes kill and eat them.
Despite their formidable appearance, tarantulas are mostly harmless. They typically prefer to remain underground or in hiding while waiting for prey. Tarantulas are one of the oldest arachnids in the world, with fossilized remains dating back nearly 235 million years.