"I put six sachets of rat poison in the cellar, one behind the boiler, two along the wall, and three days later I found the neighbours' cat ill." This homeowner from Vitry-sur-Seine sums up in a single sentence the two problems with rat poison bought at the supermarket: nobody reads the instructions, and people completely underestimate what the product does beyond its target.
The blocks and sachets sold in garden centres are not harmless products. They are biocides authorised under conditions, with a limited period of use, a requirement for a secure container, and sometimes an outright ban on outdoor use. These conditions appear on the label, in 6-point type that no one ever deciphers.
This guide won't repeat how to spot a broken drain or how to secure a compost bin: other articles on the blog cover that. It deals with one specific and very poorly understood point: what a private individual can legally and usefully do with a rodenticide at home, what they must not do, and the situations where poison is quite simply the wrong tool.
What is actually in a garden-centre rodenticide
Almost all consumer products are based on second-generation anticoagulants: bromadiolone, difenacoum, brodifacoum. They block the vitamin K cycle and cause internal haemorrhaging three to ten days after a sufficient dose is ingested.
Two practical consequences that the label never explains clearly:
- The effect is delayed. The rodent does not die on the spot. It keeps moving about, keeps eating, and dies somewhere else — often under a floor or inside a duct, hence the smell that sometimes follows a DIY treatment.
- The molecule persists in the liver. This is the whole issue of secondary poisoning: a cat, a dog, a hedgehog, a tawny owl or a buzzard that eats several poisoned rodents accumulates the substance. ANSES has in fact tightened the usage restrictions on these substances over the past several years, precisely in order to limit this contamination of non-target wildlife.
In consumer formulations, the active-ingredient concentration is low (often 25 to 50 ppm), which reduces the risk to a pet from a single direct ingestion — without eliminating it, especially for a puppy or a small cat. An antidote does exist (vitamin K1), but it is a veterinary treatment and must be given quickly: if in doubt, call a vet or the animal poison control centre; do not wait and see.
The usage rules the label really imposes
The marketing authorisations issued by ANSES set conditions that apply to private individuals, not just to professionals. The most significant ones:
| Rule | What it means in your home |
|---|---|
| Limited baiting period (often 35 days) | You don't leave blocks in place "just in case" all year round |
| Bait in a tamper-resistant station | It is forbidden to place a bare block on the floor, accessible to a child or an animal |
| Indoor use only for many consumer products | An "indoor" product placed in the garden is a non-compliant use |
| No permanent baiting | Treatment is a one-off campaign, not a long-term fixture |
| Removal and disposal of baits and carcasses | You don't leave residues in the cellar after the operation |
In other words: the mental model of "I put poison everywhere and let it do its work" is the exact opposite of what the authorisation provides for. The expected set-up is a lockable bait station closed with a key or a catch, fixed in place, with the bait secured on a rod. This is non-negotiable as soon as there is a child, a dog, a cat or poultry on the property.
And one point that many homeowners in Champigny or Saint-Maur are unaware of: organised collective control (bromadiolone used outdoors against voles, baiting in the sewer network) falls under different frameworks, governed by ministerial order and reserved for licensed operators. A private individual does not pour granules into a wastewater inspection chamber.
Mice or rats: the product choice is not the same
This is the most common mistake right at the outset. The two species do not feed in the same way.
The brown rat (sewer rat)
- Wary: it takes several days to accept a new object (neophobia). A station set out in the morning may be ignored for a week.
- A big eater: it takes a few substantial meals at a fixed spot.
- So you must leave the station in place without moving it, along a wall or a hedge, on its usual route, and accept that nothing will happen in the first few days.
The house mouse
- Curious but a nibbler: it takes 20 to 30 micro-meals a night at different spots.
- A single station in the cellar will never be enough: you need to multiply the points, every 2 to 3 metres along its runways.
- It is perfectly happy with alternative food: as long as a bag of kibble or a seed bin stays open, the bait has competition.
For a limited and recent mouse presence in a pantry, a mechanical mouse trap is often more appropriate than bait: it kills on the spot, you recover the body, and there is neither a persistent molecule nor a risk to wildlife. Set out in batches of six to ten, perpendicular to the wall, they give a readable result within 48 hours. The blog article on mice in the house in winter sets out where to place them.
The four mistakes that ruin a DIY treatment
1. Putting bait down without removing food sources
A rodenticide is a food competing with others. If there is a torn-open bag of bird seed, a bin without a lid, kibble left out overnight or an open compost heap, the rodent will choose whatever smells best. Sorting out food sources beforehand determines 80% of the outcome. This is the whole subject of our articles on pet bowls and bags of kibble and on the compost bin and the chicken coop.
2. Treating without sealing up
Killing the individuals present without closing off the access points simply frees up space. In a densely built-up residential area like Créteil or Nogent, the gap is filled again within a few weeks from the neighbouring property. A mouse gets through 6 mm, a young rat through 20 mm. The useful work is done with fine-mesh metal grille and steel wool packed into duct openings — not with expanding foam that a rodent gnaws through in a single night.
3. Handling without protection
Rodents and their droppings expose you to leptospirosis, hantavirus and salmonella. Never pick up a carcass with bare hands and never dry-sweep droppings (it puts particles into the air). Disposable nitrile gloves and an FFP2 mask, a spray of diluted bleach before collecting, a sealed bag in the household bin: that is the minimum. Cases of leptospirosis in France are documented by Santé publique France, and the risk rises sharply after flooding — see our guide after a flood of the Marne.
4. Leaving baits lying around after the campaign
A block forgotten behind the boiler for two years protects no one: it oxidises, loses its palatability, and remains a hazard for a child exploring the cellar. You remove them, count them, and throw them away.
