|MadSci Network: Zoology|
Dear Julie -
I couldn't find anything that directly states that insects perceive "pain" like humans do. However, I suspect a butterfly would feel "pain" if you stuck a pin in it for the following reasons:
1. What would you do if someone stuck a pin in you? You'd probably writhe around a lot, make some unpleasant noises, and do what you could to remove it. You may notice insects doing the same thing when noxious things are done to them - they writhe about.. make noises if able.. and will do things to try and "remove" the offending stimulus. An insect may not be able to remove an impaling pin, but may be able to do things like bite or sting the individual doing the impaling (well, maybe not butterflies..). In other words, insects appear to respond to painful stimuli in a manner similar to how we would respond. However, just because the response is the same, does not imply the "pathways" to get to that response are equivalent. Insects may "feel" something else that makes them behave in a similar manner. We can't ask them whether it hurts when we stick a pin through their abdomen...
2. Scientists know a fair amount about one insect, the common fruit fly ( Drosophila melanogaster). Drosophila is considered a "model organism" in biology. It is very easy to work with. Scientists like to use it to study complicated things such as development and genetics. As with most insects, Drosophila has ~10,000 neurons, or brain cells... not much of a brain, but look what it lets insects do! Some scientists (see references) studying the nerve cells of fruit flies have found they possess a neurotransmitter called substance P. In humans substance P plays a key role in sensing pain. It turns out that the ability to feel "pain" is quite useful. It lets you know when something bad is happening, so that you might take action to stop or prevent it. It probably appeared very early during the evolution of multicellular forms of animal life, and so is conserved throughout much of the animal kingdom. For this reason we find many different animals (humans, fruit flies, sea snails..) that have it. The fact that insects have a neurotransmitter that is known to transmit the sensation of "pain" in humans is again suggestive that insects feel pain.
They key piece of information missing is whether insects have the needed structures in terms of "nerve pain fibers" and neurons that can sense pain. As far as I can find, the MEDLINE databases have no literature on this subject. In any case, I'd recommend preferentially pinning dead butterflies only, and letting the live ones go free for another day..
-L. Bry, MadSci Admin
Ui-Tei K., et al. Chemical analysis of neurotransmitter candidates in clonal cell lines from Drosophila central nervous system, II: Neuropeptides and amino acids. Neuroscience Letters. 195:187-90, 1995
Elekes K., et al. Peptidergic neurons in the snail Helix pomatia: distribution of neurons in the central and peripheral nervous systems that react with an antibody raised to the insect neuropeptide, leucokinin I. Journal of Comparative Neurology. 341:257-72, 1994.
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