My world has zombies that are created as a result of infection with a symbiotic organism consisting of a bacterium in symbiosis with another eukaryotic organism, essentially somewhat like a lichen. The bacteria is capable of growing outside of a host and can photosynthesize. The eukaryotic organism's cells somewhat resemble muscle cells in their structure and are what is responsible for making actual zombies. The infection proceeds thusly:
- First, this lichen-like thing grows within a dead body and derives nutrients from the breakdown of various tissues that are not necessary for it to function. The growth somewhat resembles a fungus in how the organism develops tendrils throughout the body.
- Over time, bones are restructured to make the body better capable of killing other humans or suitable living hosts. Usually this manifests in the zombie growing claws or being covered in a shell of bony material.
- When the growth of the organism throughout the body is extensive enough, the body is made to move through mechanical action by the eukaryotic organism. The eukaryote essentially acts as a puppeteer.
- This zombie then goes on to kill other living things to provide more hosts for the organism.
This organism can grow on walls and floors, but this is terribly inefficient compared to using living things as food. In times of food shortage, the zombies can derive some nutrition from the bacteria growing in the environment. The parasite is also capable of entering a state similar to hibernation to conserve nutrients. If anything were to die on top of or next to a "mat" of the stuff, it will become infected. The organism also releases toxic products into the air, which would help it get more bodies to infect.
Because the zombie consists of a parasite acting mechanically upon a host body, shots to the head cannot kill it. The only way to kill such a zombie is to completely destroy the body, burn it, or use a chemical or biological agent that attacks the actual zombie organism. However, the organism typically cannot infect a living human, as the immune system would be able to eradicate it, hence the need for the host to either be dead, immunocompromised, or receive a massive dose of the infectious agent.
I am having trouble thinking of how such an organism would actually locate victims. The requirements for the zombies' method of finding prey are that they cannot rely on the host's sensory organs or nervous system being intact, and they cannot be fooled by a simple trick such as throwing an object to make a sound. I briefly considered having them seek victims by sensing chemicals that are released by living humans or other creatures, but this has the downside that anyone wearing a chemical protection suit would essentially be invisible to them. I also considered having them sense vibrations indicative of movement and/or having them sense infrared emissions, but I am not sure if this is possible for such an organism.
So, how can my zombies sense prey? The nature of this organism is not set in stone, so feel free to offer alternatives.