All animals respond to stimulate that causes them discomfort. For instance, insects will move away from heat that is likely to damage them. All insects have senses that are triggered by stimuli and a nervous system that translates stimuli into a response. The complication is whether this can be described as pain, or if it is just an automatic response. To feel pain do you have to be conscious of the sensation and able to decide how to react?
Currently, the British legal system does not recognise pain in invertebrates, accepting the argument that as there is no evidence that invertebrates are conscious of their predicament, are hence unable to be conscious of pain, and therefore do not feel pain. This is reassuring because the numbers of insects and other invertebrates that we maim and kill on the front of vehicles and on the leading edge of ploughs is staggering.
Matt Shardlow, chief executive, Buglife: The Invertebrate Conservation Trust