If you've ever lived where there are cicadas, you know that these extremely noisy insects make the most racket when it's blistering hot. How do they keep cool while remaining so active in the hot sun? The secret is that cicadas sweat. These finger-long, winged insects have pores through which they secrete a watery liquid derived from the tree sap they drink. While they sing (by vibrating ridged membranes against their bodies), they sweat profusely, thus dissipating the heat of their efforts. Those efforts result in the loudest sounds made by any insect. In Missouri in the summer of 1999, the din reached 85 decibels at some locations, louder than a large diesel truck at full power. Outdoor cafes had to close because the noise was too much for the customers.