Encyclopedia of Opinion
Question
Why are there so many mice in London?
Position1 of 5›
London mice are resistant to rodenticide
Argument

Extended use of rodenticides has lead to resistance for London's mice

Because of the widespread use of poisons to control London's rodent population, mice have become resistant to traditional rodenticides.

The argument

Mice have always been prevalent in London. Given the city's longevity, mice have had countless generations to adapt to their surroundings. Mice reproduce quickly, a single female can have up to 10 litters per year with 5-6 mice per litter. As people began to fight the mouse problem in London with anticoagulant rodenticides in the 1940s and 50s, the mouse population was initially reduced to a fraction of what it was before. However, scientists observed in the 1960s that the mice that remained after the use of these rodenticides had developed an immunity to the poison--even genetic mutations to protect themselves--and the latter quickly reproduced. A A similar thing happened with a later-developed compound known as bromadiolone. This gave rise to a mouse population in London that was mostly immune to these previously commonly used anticoagulant rodenticides.

Context

Traditional rodenticides are typically anticoagulants, which kill mice and other rodents through excessive internal bleeding. While there are other types of poisons--not to mention other methods of controlling mice populations--anticoagulant rodenticides are some of the most commonly used.

Premises

[P1]London's mice reproduce rapidly over countless generations, and the anticoagulant rodenticides used since the 1940s killed the susceptible majority while leaving resistant survivors. [P2] By the 1960s scientists observed these survivors had developed immunity—even genetic mutations—and quickly bred a population mostly immune, a pattern repeated with the later compound bromadiolone. [C] Therefore extended use of rodenticides has led London's mice to become resistant.

Counter-arguments

Saying that mice are resistant to rodenticides is oversimplifying the matter because there are many poisons, even anticoagulants, that can be very effective in controlling mouse populations. Just because London's mice are now resistant to some compounds like Warfarin and bromadiolone does not mean that this fully excuses or explains the city's current mouse problem.

Rejecting the premises

[Rejecting P1] Selection acting on survivors is the right mechanism, but the premise gives no figure for how much of London's mouse population actually carries resistance — rapid breeding explains how a trait spreads once present, not that it is now prevalent. [Rejecting P2] Anticoagulant resistance was first characterised in rats, and the later compounds were developed precisely to overcome it, so as the counter notes resistance to two named poisons does not show that rodenticides in general have stopped working — and none of it touches the sibling positions on waste, buildings and the size of the city.

Further reading

More on mice: https://bpca.org.uk/a-z-of-pest-advice/mouse-control-how-to-get-rid-of-and-prevent-mice-bpca-a-z-of-pests-/189003#the-dangers-of-mice Rodenticide Resistance Action Group (RRAG): bpca.org.uk/about/partners/rrag