Birds of Prey

They float from planet to planet. A dozen generations are born and die in the vast expanse of space as they travel to their next target. A dozen more pass while they feast on a planet, and the cycle continues. They feed on life, more specifically the electrical impulses that living things give off. These creatures, these... birds of prey, are infamous for their lethality. Entire planets have been turned into floating rocks because of them, and it takes considerable loss to hunt a singular one - let alone the whole species. The intergalactic community identified a pattern in their movements, a route just long enough that by the time they reach the end, the first planet is ready for harvest. They stay out of their way, they leave them alone, and Earth is one of many left to fend for itself.