Insects push the boundaries of smallness. Midnight movies to the contrary, there's only so large an exoskeleton-based creature can grow — theoretically, around 4-5 ounces (125-150 grams) [source: Meyer]. The largest living insect, the cricket-like New Zealand giant wētā, or wētāpunga, weighs about half that (but still outweighs a mouse or a sparrow!) [sources: NZDoC, The Telegraph ].
One the smaller end of the scale, insects are wonders of miniaturization. Shakespeare's Hamlet spoke figuratively when he said, "I could be bounded in a nutshell, and count myself a king of infinite space." But some ant species establish entire colonies inside of acorns [sources: CISEO; Meyer]. Moreover, the smallest insects, such as the Costa Rican wasp Dichomorpha echmepterygis, can reach sizes smaller than some paramecium (single-celled protozoa) — 0.00055 inch or 0.139 millimeters. The majority of insects fall into the 0.1-1.0 inch (2-20 millimeter) range [source: Meyer].
Tiny creatures enjoy several advantages. They need only the tiniest morsel or drop to sustain their bodily needs, hide from predators in nearly any setting and find shelter and shade wherever they might be. To them, a pebble is a boulder and a tiny crack, a fissure. You might say that, for insects, the world is incredibly small and therefore unspeakably vast.