Wolves communicate other things with their bodies, too. If they are angry, they may stick their ears straight up and bare their teeth. A wolf who is suspicious will pull its ears back and squint. Fear is often shown by flattening the ears against the head. Wolves have a very good sense of smell, which they also use to communicate.
Wolves mark their territory with urine and scat.
This is called scent marking. Of course their sense of smell also tells them when food or enemies are near. That is one of the ways wolves communicate with their voices. Wolves don't just really howl at the moon. They will howl any time of the day, but are most often heard in the evening because that is when the pack is most active.