Zombies are their own genre and have many tropes associated to them. There's plenty of questions on here that deal with surviving a zombie apocalypse, but they all assume that zombies are capable of surviving for extended periods of time. Unfortunately zombies rely on human fysiology, so all the rules for requirements of (relatively) fresh water, food and shelter apply to them as well. This makes zombie apocalypses a bit of a sad affair when the rules for surviving one are "wait a couple of days and they'll die of hunger, thirst or the weather".
To remedy this, I would like to design a zombie that can actually pose a threat to humanity and serve as the long-term threat that they are overall. For this to work there's a bunch of constraints and requirements the zombies need to adhere to so it's neither too hard or too easy for a zombie apocalypse.
- Zombies need to survive for at least 20 years from adolecense (most points after will deal with this).
- at least 50% of the human population must turn into zombies, things like the WHO or the army should not be able to stop the zombies from reaching this % even though they'll try. More would ofcourse be better. A 100% conversion/kill rate is also not allowed, at least 5% of the human population needs to survive to deal with the zombies.
- Armies around the world need to be infected too or dealt with otherwise. Army bases tend to be rather zombie-proof and they would have a good chance of wiping out the zombies way too fast.
- Zombies need to survive the weather, a few hot days or a winter shouldn't kill them off.
- Being a Zombie is transferable similar to contact diseases like SOA's during it's main stage where it has control of 50% or more of the human population, but not other methods. For those not in the know, SOA's are also transferably through saliva or blood to blood contact so these zombies do not need to rape their victims (I'm sure someone would have this idea).
- Being a zombie can be tranferable by other methods before it reaches the 50% population, but needs a plausible reason why it stops using those methods.
- Zombies may be smart enough to use simple tools. This is probably a prerequisite for any zombie, as the simple act of "all zombies can remember to put on winter clothing during cold and protect themselves from the sun during warm weather" is likely to be one of the few (if not only) successful way to ensure the world remains unsafe. For vehicular usage, zombies are allowed to use vehicles but only in mostly straight lines with turns a maximum of 45 degrees at a time, all actions while driving (like braking) would take several seconds for a zombie.
- During the main stage, being a zombie cannot be transferred by animals of less than 50 kilograms when fully grown (a child of an animal that will eventually reach 50 kilograms or more can be infected). This is mostly to avoid scenario's where mosquito's and rodents infect and zombiefy most of the world. These animals either die before they can transfer the disease further or are immune and not carriers (should you want to use these as a source of zombie-food).
- For water, zombies are allowed to drink water from streams of moving water not connected to polluted waters like the sea or polluted lakes. Rain is also allowed.
- For food, zombies can eat anything humans can.
- Zombies will be highly resistant to diseases and infections, if you have a legitimate reason to make this happen then please add this. This requisite is added because zombies would have too high a likelyhood to die after being turned into a zombie from the injuries they sustained and the lack of medical attention they get. Also the lack of desinfected food (cooked for example) would be likely.
- If you can make it reasonable, you are allowed changes to flora and fauna that will help sustain the zombies through food.
- if necessary, zombies are allowed to procreate.