Compared with them, we humans are terrible wimps
Children -and a few adults as well- are known to have sometimes plucked off the wings of flies, heaven knows why. Housewives do not hesitate emptying spray cans of insecticide over ants in the kitchen and gardeners can go berserk over aphids on their precious rose bushes and would try to annihilate the pest with all the chemical weaponry available. Isn’t that cruel? Are the insects not suffering pain and distress? Let us examine.
An injured mammal with pain in one of its legs tries to protect that leg by limping, putting as little strain on it as possible. The mammal is also likely to remember the cause of the pain and will try to avoid an injury the next time it encounters the cause of its earlier discomfort. That certainly makes sense in animals with long life span, as there is a chance they will someday once again face the earlier painful stimulus. An insect, however, possesses largely pre-programmed behavioural patterns, leaving much less scope for individual learning processes. Insects need not remember as much as a mammal, for they are -on the whole- much shorter lived and their capacity to remember things is therefore generally less well developed.
An insect with a crushed foot does not in any way protect it and will use it as if it were intact. Hungry wasps sipping from a food source, can have their abdomens carefully severed off and will continue to feed without apparently displaying discomfort or noticing that half of their body is missing. Under experimental conditions, it has been reported that starved caterpillars could be induced to nibble on their own rear ends. Does that prove the non-existence of pain? Perhaps not by itself, because insects do, of course, react to rough handling, electric shocks, excessive exposure to light and temperature, but the responses need not be pain, but more likely represent a kind of reflexive withdrawal. Moreover, it needs to be remembered that “nociception” does not mean the perception of pain, but the conduction of signals that lead to the sensation of pain.
Another argument against the presence of an elaborate sense of pain in insects is their small size. The nervous system of these small arthropods consists of cells of the same size as in mammals, but while in mammals often about half of the total number of sensory neurons is estimated to be involved in pain reception (with the exception of the beautiful naked mole rats of the family Heterocephalidae that appear to lack a sense of pain), there simply is not enough space in the smaller insect nervous system. For reason of economy then, pain appears to have been sacrificed in favour of the perception of light, sound, temperature etc.
Not to be misunderstood: I do not condone any cruelty to insects (although I am not a friend of mosquitoes) and even find it distressing to see an insect writhing as if in agony after it’s been poisoned with insecticide, but at the same time I do find it scientifically acceptable that certain animal species should have particular sensory strengths. In case of the dog it’s smell; in bats and owls it’s their hearing: in the rattle snake it’s the sense of temperature, but we humans are definitely the pain champions, the “cry babies”, the wimps of the animal world, which the insects clearly aren’t.
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2017.
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