Both mice and rats are killed using similar types of poisons, known as rodenticides. These poisons act as anticoagulants, dramatically reducing the blood’s clotting ability until the rodent dies from internal bleeding. After ingesting a lethal dose of the poison, mice take between three and ten days to die, depending on the amount of poison consumed.
Because these poisons take several days to work, poisoned rodents can end up dying some way away from where they actually consume poisoned bait. A dead mouse will decay rapidly in a warm environment, creating a distinctive and very unpleasant odour as they do so. If the mice have already built a nest, you will find most of the carcasses in its vicinity. However, there’s no guarantee that the mice will die in a location you can easily reach; they could just as easily die behind your wall cavities or in your vents.
One of the reasons that anticoagulant poisons are used is because they accelerate the decomposition process. This means that mice will start to decay sooner, but it will also take less time. Overall, this should lead to fewer odours and a less unpleasant experience for the user. After the poison has begun to take effect, poisoned rodents will soon lose their appetite and are unlikely to eat more poison after their first dose.
In the UK, pest control professionals have access to more potent rodenticides than the average consumer. Professional-grade mouse poison should only ever be deployed by a trained professional who understands the risks and how and where to use it appropriately. If a contractor lays any mouse poison down in your home, they will advise you of any precautions you need to take to keep your family and pets safe.