When most calls you get are somewhat of an emergency, how do you handle that!?

I own and operate a pest control business, and anyone who has ever needed to call pest control, they typically want you there right away! I am sure there are other companies that operate under the same stress, and I wonder how they manage those calls that come in during a planned out day? Or calls that come in at the end of the day. Calls that come in on a Friday afternoon. Calls that come in during a busy week!