Cicadas are very interesting insects. Nicknamed "Tree Locusts" though no relation. After 13 yrs underground they emerge as adults and the males make a loud noise. I haven't recently paid attention to what a cicada was until my recent trip to Virginia - in which my friends' home had their loud noise and you can see them and hummingbirds about their yard. It was a very fascinating thing - to hear and see - in which you don't get to see them but every 13 (or some 17yrs)
What type of animal or insect did you last find fascinating?