While the human chemical assault on insects began 4500 years ago in ancient Mesopotamia with the use of sulphur insecticides, plants have been doing it for far longer.
The evolutionary arms race between plants and insects goes back as long as they first appeared on Earth.
It's believed that insects originated in the Ordovician period about 480 million years ago, about the same time as terrestrial plants.
A synthetic chemical such as DDT never existed in the environment, which means there are no natural processes to break it down and therefore it persists long after it's been applied.
Pyrethrins, on the other hand, are derived from chrysanthemum flowers which are naturally occurring and break down rapidly. As early as 1000 BC in China, chrysanthemum plants were being powdered for use as an insecticide.
However commercial insecticides commonly combine pyrethrins with synthetic chemicals such as piperonyl butoxide to make them more effective.
The question of what an insect feels when sprayed with pyrethrum is a very tricky one. It can be difficult enough to understand another human, let alone a creature that diverged from mammals hundreds of millions of years ago.
They do, however, have a brain, albeit far smaller and simpler than ours.
Located in the back of the head, it consists of three pairs of lobes called the protocerebrum, deutocerebrum and tritocerebrum.
They process sensory information in clusters of neurons, each controlling different functions.
While a common fruit fly has 100,000 neurons and a bee has 1 million neurons, a human brain has about 86 billion neurons.
Pyrethrins have a powerful effect on their nervous systems as it causes their neurons to become hyper excited, firing chaotically. Death occurs rapidly as it loses motor coordination and becomes paralysed.
One imagines that it would feel like an extremely powerful - lethal - jolt of electricity.
While no one reading this has ever (by definition) been electrocuted, you'll have a sense of this if you've ever touched a mains power outlet.
Although the frantic batting of a blowfly against your window gives a clue to what they're experiencing, their consciousness is remotely different to ours.
This story tells us something about our ethical judgements: that one dimension we consider important is the other being's ability to be aware of its suffering.
Should we treat a creature that is conscious differently to one that isn't? And what does "conscious" mean anyway?
Next week we consider whether the artificial intelligence called LaMDA is sentient.
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