Well thats ur opinion some people might not think it is hard
There are two sets of nerves in your skin. The first type are somatosensory neurons that send sensory information to your central nervous syste. The second set consists of autonomic fibers that control smooth muscle in the skin and the blood vessels in the skin.
The cause of the change in insect characteristics occurred when a few survivors of the 1st spray became resistant to the insecticide. When they had offspring, those insect babies are born with the trait that made them resistant to insecticide. This occurs when the parents pass on the trait to their offspring. The end result is that the insecticide is less effective and more insects survive.