Rat poison comes in various different forms and formulations and is becoming harder for the general public to purchase in any other than small pre-packed ready to use sachets.
Rats prefer to eat bait that is highly palatable. The sweeter the bait the longer the rat will feed, rats mainly feed in the dark and baits have added aromas that rats find highly attractive.
How it works
The three most common active ingredients readily available are difenacoum, bromadiolone and brodifacoum which are all anti-coagulants. These poisons affect the rodents blood clotting response, so after a few days the rodents will die as a result of internal haemorrhaging.
The poison effectively thins the blood to the extent that blood seeps internally from tiny blood vessels and organs quickly resulting in heart failure which ultimately kills the rat. The rodents feel fine, suffering no pain and therefore they continue to feed as normal, consuming a lethal dose before succumbing to the effects of the poison. This is important, as rats in particular will quickly stop eating anything that they associate with danger.
How long does it take rat poison to work?
This depends on how long it takes a rat to ingest a lethal dose of whatever poison you use. Once a lethal dose has been eaten, death occurs typically within 3-5 days. A lethal dose of difenacoum is considered to be 9g, of bromadiolone 5.6g and of brodifacoum 1.4g. A typical rat will eat 25-30g a day over about 10 meals.
Which poison should I choose?
The first consideration is whether you need to bait indoors, outdoors or both. Some baits can only be used indoors. Then decide which formulation you need. Grain baits are only available in sealed sachets, but are handy to throw into inaccessible areas, where non-target species will not encounter them. Blocks are the bait of choice as they can be secured into bait boxes and kept safe from any non-target animals, pets and children. As detailed above, different active ingredients have higher consumption levels before they become lethal. A lot more difenacoum needs to be placed to kill a rat than brodifacoum, and possibly for longer. This could affect the decision as to which one to buy.
Which poison is strongest?
The safety of rodent bait recently came under review by ECHA, the European Chemicals Agency. There were too many cases of secondary poisoning of non-target species such as owls, stoats and foxes. As a result, the maximum level of active ingredient in any poison available to the public was reduced from 50 parts per million (ppm) to 25 ppm. This was instigated to reduce the concentration of poisons in the environment. So no one bait is 'stronger' than any other. What differs is how much of a bait is required to attain that lethal dose.
I have small children and pets at home. Is it safe to use poison?
Yes. If you read the label and comply with it, any poison can be used around the house and garden safely. Of course, extra care needs to be taken to keep young children away from the baits. A lockable bait box is mandatory for all amateur users at all times. If you have pets, exclude them from the baiting area and check for any loose pieces of bait outside of the exclusion zone (and any dead rodents) before letting them back into the room or garden.