Bugs may be a pain to us, but they feel no
pain. Pain is officially defined as, "An unpleasant sensory and
emotional experience associated with actual or potential tissue
damage". It is experienced differently by each person and organism.
Because of this it is extremely difficult to describe just how an
animal experiences pain.
To study how an animal experiences pain, argument-by-analogy is
applied. This means if the animal reacts in a similar way to how we
would, we believe they are experiencing pain. An example might be if
a dog is pricked with a pin and runs away, as a human would.
Insects have no capacity to feel pain. Nociceptors are what carry
the feeling of pain to the brain. These are essential to experience
pain, yet insects and crustaceans have never been found to have any
nociceptors. This means most of these animals are unable to feel any
sort of pain. Most insects do not possess nociceptors. I knew
when I squished them they were not yelling.