I think tiger beetles, dragonflies, and robber flies are pretty cool. Jumping spiders are also pretty interesting, but my favorites are probably ants. I remember when a local museum had an exhibit dedicated to army ant colonies, and that was pretty intriguing. Now that I think about it, the trap jaw ants of the genus Odontomachus are pretty cool, with their propulsion and expelling of enemies just by closing their mouths being fascinating.
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"As buds give rise by growth to fresh buds...so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications." - Charles Darwin, The Origin of Species