Wolf spider Alopecosa sp. encounters grasshopper Melanoplus sp. on log in Ohio. Spiders have poor vision and rely on movement to detect prey. The grasshopper is safe as long as it doesn磘 move. This one remains motionless, even when touched by spider, not hopping away until the danger has passed. Wolf spiders get their name from the way they run down their prey, like wolves. Most species don磘 spin webs. They are found throughout the world.