A creature that has a climb speed, such as a spider or a carrion crawler, doesn’t have to make Athletics checks to climb. It can simply climb up and down a surface using its climb speed, doing so as part of any of its actions that involve it moving. In addition, the creature ignores difficult terrain during the climb and doesn’t grant combat advantage because of climbing. For rules on climbing, see “Athletics”.
Published in Monster Manual 2, page(s) 216, Monster Manual, page(s) 280, Rules Compendium, page(s) 309, Monster Vault: Threats to the Nentir Vale, page(s) 122.