Hillbilly zombies have 30 Health and are the strongest zombies encountered so far. They do not need to be killed with crafted weapons, but it will be a challenge and expensive to kill them with any weapons you have. Using Grenades, the China Lake, Flare Gun, and Bazooka are the fastest methods so far, but can be costly. Hiring friends to weaken them is useful, as well as placing several Land Mines around them. Fortunately, they are only encountered in special scenarios requiring you to kill them to complete an objective. Once completed, they only return when you need to kill them again.
Daisy seems to be related to several of them, and she often asks you to help lay them to rest.