Pain, suffering and euthanasia

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    I often get asked how to euthanase a butterfly And if butterflies (or caterpillars) feel pain.

    Firstly remember that we (hot blooded human beings) like to live or be in a comfortable temperature and so when it’s cold or too hot, we complain. But butterflies and other invertebrates are cold-blooded so they are active when it’s hot, but inactive when it’s cold.

    On a wet, stormy day they’re not complaining as we do. They are. Some of them will die in the snow or in a cyclone, but that’s Nature.

    Pain, by definition, requires a capacity for emotion. According to medical scientists pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. It’s more than the stimulation of nerves – people can feel and report pain with no actual physical cause or stimulus.

    Pain is a subjective and emotional experience. Our response to unpleasant stimuli is influenced by our perceptions and past experiences.

    The nervous system of an insect differs greatly from that of higher order animals. Insects lack the neurological structures that translate a negative stimulus into an emotional experience. People and other mammals have pain receptors (nocireceptors) that send signals through our spinal cord and to our brain. Within the brain, the thalamus directs these pain signals to different areas for interpretation. The cortex catalogues the source of the pain and compares it to pain we’ve experienced before. The limbic system controls our emotional response to pain, making us cry or react in anger. Insects don’t have these structures suggesting they don’t process physical stimuli emotionally.

    Most people learn from our pain (well, usually, LOL) and change our behaviour to avoid it. If you burn your hand by touching a hot surface, you associate that experience with pain and will avoid making the same mistake in the future. Pain serves an evolutionary purpose in higher order organisms. Insect behaviour, in contrast, is largely a function of genetics. Insects are pre-programmed to behave in certain ways. The insect lifespan is short so the benefits of an individual learning from pain experiences are minimised.

    Perhaps the clearest evidence that insects do not feel pain is found in behavioural observations. How do insects respond to injury? An insect with a damaged foot doesn’t limp. Insects with crushed abdomens continue to feed and mate. Caterpillars still eat and move about their host plant even with parasites consuming their bodies. Even a locust being devoured by a praying mantis will behave normally, feeding right up until the moment of death.

    Therefore when we consider euthanasing an insect it is more to stop the spread of any disease that it has, not to put it out of pain. The pain WE experience at the death of anything – even an insect – is, however ours and ours alone.

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