An eater is any still life (or, less commonly, an oscillator) that has the ability to interact with certain patterns without suffering any permanent damage. The term may also sometimes specifically refer to eater 1, a very common and well-known eater. The block was the first known eater, being found to be capable of eating beehives from a queen bee, allowing the construction of the queen bee shuttle. The animation to the right shows an eater 5 feasting on an incoming stream of gliders.
Eaters are extremely important, as they help stabilize and control debris created by complex reactions, allowing for the manipulation of the useful parts of those reactions. Stable reflectors in particular heavily rely on a variety of eaters to work.
A rock is a term coined by Dean Hickerson that describes an eater which remains intact throughout the eating process (that is, it does not suffer even temporary damage while eating). The snake in conduit 1 is an example. Other still lifes that sometimes act as rocks include tub, hook with tail, eater 1 (when eating with its tail), and hat (in Heinrich Koenig's stabilization of the twin bees shuttle).
Glider eaters by recovery time
There are dozens of known glider eaters with varying recovery times. The smallest known recovery time is 4 generations, attained by eater 1. The following stamp collection, compiled in December 1998 by Dean Hickerson, displays 88 well-known glider eaters arranged by their recovery time. Some of the most notable eaters displayed are eater 2 (leftmost in the "5" row and second from the left in the "6" row), eater 3 (leftmost in the "9" row), and eater 5 (second and third rightmost in the "6" row). Additionally, the leftmost eater in the "10" row and the second rightmost eater in the "11" row both produce a 1-bit spark, which can be useful.