The older flay sprays used to interfer with a transmitter called acetyl choline in the fly's central nervous system
Yes they are convulsing
Pain does not really have meaning in insects
If you have a feeding locust and chop it in half
it goes on feeding
Most people would conclude that as result of no reacction then it does not feel pain.....just n case you wondered if all those flies suffered before they died
Some fly sprays use a chemical (I forget its name) that remains as liquid droplets in air, but that will create large flat crystals when settling together on a solid surface. The droplets are breathed in by the flying insect and the crystals spread over the surface of their equivalent of lungs. So the insect suffocates.
Domestic insecticides often use plant-derived insect toxins such as pyrethrum. These nerve toxins seriously affect the insect's central nervous system and they convulse and die. Presumably the effect is similar to that of "nerve gas" on humans.
There are a number of different chemicals used in household fly-sprays and they do differ in their mode of action.
Dichlorovos/DDVP is one of a group of chemicals known as acetylcholinesterase inhibitors. Acetylcholinesterase is an enzyme in nerve synapses which stops nerve impulses after they have crossed the gap between nerve cells. Acetylcholinesterase inhibitors lock onto the enzyme and prevent it from functioning. This results in a continuous stimulation of the nerve cell which cause tremors throughout the body of the insect. These tremors and uncoordinated movements lead to the death of the insect.
Permethrin and Tetramethrin are two other common insecticides in fly-sprays. These are known as pyrethroids and are synthetic forms of a naturally occuring insecticide called pyrethrin. Pyrethroids are called Sodium Channel Modulators and work by binding to a protein called the voltage-gated sodium channel. Under normal circumstances, when this protein is opened the nerve is stimulated and when it closes, the nerve signal is terminated. Pyrethroids lock onto the gate and stop it closing. The nerve is then continuously stimulated leading again to tremors and death.
There are also other insecticides in fly-sprays such as piperonyl butoxide which has an entirely different mode of action.
I heard something like: 'Flys breathe through tiny pores which cover their bodies, the fly spray blocks the holes, thus suffocating them.'
Don't know if it's true, if I read it, saw it or just dreamt it. I have a very vivid imagination and a degree in engineering. Trouble is, I can rarely tell the difference between what I have been taught and what I have imagined. Doh.
You're partly right, Muppit. Some insects breathe as you say, but most breathe through small holes on their sides. These are the 'spiracles' mentioned above. For a good description, scroll down to 'Breathing' here
I have very rarely dreamt that I was reading a textbook - very troublesome in fact, as you/one then memorises complete cr+p ! A dream as reality, a real pain in the a+se
As luck would have it, in exams they rarely ask me about things I have dreamt. So the only things that really apply are things that I have been taught! (I think that on the odd occasion when I do write something that I have dreamt it just blows the examiners mind because it is so radical)