This is a classic work, and well worth reading. It puts the lie to the common statements that "if an ant were as big as a man, it could lift incredible loads!" If an ant were as big as a man, it would collapse under its own weight.
HTML version: http://irl.cs.ucla.edu/papers/right-size.html
Interesting earlier discussion of the same article here under a different URL: https://news.ycombinator.com/item?id=6545132
And here's another link that includes the same article as well as many others: http://www.arvindguptatoys.com/arvindgupta/rightsize.pdf