Rats, mice and other pests in Project Zomboid

Yes, partly. Build 42 added rats and mice as real animals in the world. Earlier builds had dead mice and rats only as items from traps; in Build 42 they are part of the animal system and can be hunted, trapped and butchered. The Indie Stone lists rats alongside sheep, pigs, rabbits and deer in its Build 42 feature overview.

Other pests are simpler. Flies and maggots are tied to rotting corpses, and maggots are an edible item. We found no source for mosquitoes, ticks, cockroach infestations or any insect that bites the player in Build 42. There are also no cats or dogs to keep rodents down, as far as any source we checked shows.

Rats do not sit in every house from day one. In a September 2023 development blog, The Indie Stone explained that rats spawn procedurally as you explore, and that the world drifts toward a "Maximum Rat Index" as days pass. At that point rats have their highest spawn chance and show up in bigger groups. They can spawn with trash, trash containers and corpses, and some buildings get randomized rat stories with filthy supplies and destroyed loot.

The blog gave about two months as the default time to reach the peak. Current Build 42 sandbox lists show a default of 90 days instead, so the default seems to have changed since that post. Either way, the practical result is the same: a house you loot in week one is cleaner than one you open in month three.

Infested buildings were planned with their own sound design: rats in the ceiling and walls, gnawing, and scurrying across floors. Treat those sounds as the main warning sign. Wild animals in general also leave tracks and droppings that you can follow when hunting. We could not confirm a separate rat-droppings item that marks infested houses, so do not rely on one.

This is where older forum posts and real Build 42 behavior split. Players have long asked for mice that chew through rice and crackers in cupboards. That request is still a request: we found no source showing that rats or mice eat food in your containers, raid your fridge, or spoil stored meals in a base you have cleared.

The confirmed damage is limited to loot you find. Rat-story buildings can hold ruined or unsanitary supplies, so check what you pick up in an infested house. We also found no source saying rats eat growing crops. Crop problems in Build 42 come from weather, season and plant care, which the farming guide covers.

Sealing food still matters, but for spoilage, not pests. Fridges, freezers, canning and drying are what keep food edible; see food preservation.

You can attack rats directly like any small animal. For a steady catch, use the mouse trap, the only trap that takes mice and rats. One trapping guide says it cannot be crafted and only turns up as loot (one source). Every trap needs fresh bait, and a trap only rolls for a catch while its square is unloaded, so walk away after setting it.

The same source gives zone weights that favor farms and trailer parks for both species, with towns close behind and forests poor. Mice and rats are active all day, so there is no time window. A catch can come out alive or as a dead mouse or rat. Early mouse traps are a common way to start leveling Trapping.

Opinion Clear trash bags and corpses from around your base, since those are where rats spawn. Pick a base you claim early, before the rat index climbs.

Dead rats and mice are food. In Build 42 small animals go through the butchering system for a small amount of meat; cook it before eating like any raw meat. We could not confirm exact meat weights for each species in Build 42, so check the item in game.

Maggots can be eaten raw in an emergency or used as fishing bait. Foraging can also turn up insects such as crickets and grasshoppers. Opinion These are calorie scraps; a single rabbit is worth more than a pocket of bugs, so use insects as fishing bait unless you are starving.

Rats sit in the Animals section of sandbox settings, now labeled as a vermin index. Maggots and corpse decay are under character, health and food.

All defaults above are the Apocalypse preset values from one sandbox reference (one source). Setting the vermin index to 0 should remove infested-building rats; we have not tested this. Flies have no setting of their own.