Biology Question #13

Carla Poot, a 18 year old female from the Internet asks on May 13, 1999,

Why can't an insect grow large enough to terrorize a city?

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The answer

Barry Shell answered on May 13, 1999

Geometry is the major reason that small things cannot just grow to enormous size. Simply by growing larger, an object that keeps the same proportions will suffer a continual decrease in relative surface area and a tremendous increase in the effects of gravity. These changes occur because volume increases as the cube of length (length x width x height), while surface increases only as the square (length x width): in other words, volume grows more rapidly than surface. And as volume grows so does mass--or the relative weight of the creature compared to its bones or exoskeleton.

Insects breathe through their skin, or pockets in their skin, so if the decrease in relative surface area to volume continues very much, they cannot breathe. Also, their weight would become too great for their thin exoskeletons to hold them together. There are many great explanations of why insects cannot grow to be monsters all over the Internet, but one very good one is given by Steven Jay Gould at Natural History Magazine. Recommended reading if you want a thorough and clear explanation.

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