Dear Straight Dope:
One recent lunch conversation brought up an interesting observation. Nobody at our table can ever recall seing a fat insect. So the question was raised, "Can insects get fat/obese?"
Jerry in PA
Since insects have their skeletons on the OUTSIDE (an exoskeleton), their maximum dimensions are pretty much fixed. Certainly many insects are "fatter" when they’re recently fed or full of eggs, but this condition remains only so long as they have a full gut/batch of eggs. It would be more appropriate to call them "bloated"–"fat" implies a chronic condition rather than temporary. The closest thing would be termite queens, which become permanently swollen with eggs and immobilized.
There is a definite limit on how much an insect can expand. A fly that has had the stomach nerve cut (so it cannot tell when it is full) will eat until, like the infamous Mr. Creosote, it bursts, though not quite so explosively. Cecil claims that, under certain circumstances, mosquitoes will do the same.
Send questions to Cecil via email@example.com.
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