Most spider webs work through chance: The spider erects an invisible trap and waits until some unlucky insect hits it. But a common Australian spider called the St. Andrew’s Cross—known for its striking, cross-barred web—is sneakier.

Scientists in Spain and Croatia have found that certain spider species that feed, breed and travel upside-down are more energy efficient because of it. For the spiders, it turns out, walking is more of a swing—they use gravity to their advantage. They effectively act as a pendulum, and require less muscle mass in the legs to move themselves forward.