When a complex system reaches a tipping point, its state can change dramatically.

In the 1950’s, people in Borneo suffered a malarial outbreak, so the World Health Organisation (WHO) sprayed DDT to kill the malaria-carrying mosquitoes.

The mosquitoes were killed but the DDT also killed wasps, geckos and cats, leading to a rat population explosion, along with outbreaks of typhus and plague.

To cope with these problems, the WHO parachuted live cats into Borneo. This was Operation Cat Drop, and is an example of how tipping points in populations of pests and predators can have sudden large impacts on complex systems. An increase in favourable conditions for rats and disease to flourish represents a dramatic change in the state of a system and demonstrates how nonlinear processes are important in the dynamics of pest outbreaks.

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