Q: Why are blood thinners used to kill rats?
Most of us consider vomiting about as fun as slamming our finger in a car door. I agree! As a child, my chronic queasiness as a passenger in cars and boats bloomed into an Olympian-level hurling event more times than I ever want to recall. What humans don’t often appreciate about the ability to vomit is how useful it can be. I can hear you asking, “How can upchucking be considered a positive thing?” Barfing saves lives…Who knew? The main reason overindulging adolescents and young adults don’t die very often from alcohol poisoning is the ability to vomit it out (as in, “praying to the porcelain god”) before the booze is completely absorbed into their body .
Rats are able to eat almost anything, but unlike humans, they can’t vomit up spoiled or poisoned food. One reason rats are hard to exterminate is they are very hard to successfully poison. their habit of eating only a small amount of a new food source at a time. They sample the food and if they become sick they’ll avoid eating any more. Another reason rats are hard to kill with poison is their sensitivity to taste and smell. To be successful, any rat poison added to food or bait has to be odorless, practically tasteless, and have a delayed action.
Oral anticoagulants like warfarin and its coumarin relatives are effective rat poison because they lack a noticeable odor or taste and have a delayed effect of several days, making it hard for a rat brain to connect a particular ingestion to its eventual cumulative effect of major bleeding.
When warfarin and coumafuryl were first used as rodenticides, there was a significant variation in how much they reacted to the blood thinner. Unfortunately, a small percentage of rats were able to survive; in fact, some rats were pretty resistant, taking up to 10 times the usual dose in order to experience its anticoagulant effects. It’s interesting that a small number of people (humans, not rats!) that take warfarin also have a genetic variation that requires them to take over 10 times a typical dose in order for warfarin to be effective at thinning their blood.
Rats resistant to these early coumarins triggered the development of more potent, second generation anticoagulants called “superwarfarins”, such as brodifacoum, difenacoum, bromadiolone and difethiolone. Brodifacoum is the rodenticide used by more than 50% of professional pest controllers in the United States.
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Many people in my area are using the newer poisons for Warfarin-resistant rats. Some of my neighbors put dead rats in the compost. Others double-bag the rats and put them in the garbage. Is it safe to compost a poisoned rat? Does composting break down the poison?
Thank you.
If your neighbors use one of the rat poisons that contain a “superwarfarin”, that poison doesn’t break down very quickly and any animal that eats the dead rat is at risk for being poisoned. I would double bag it and put it in the trash.