Pic above: bees making a beeline for collecting water
Desert cooler works on the principle of water evaporation. It is also called a evaporative cooler. The temperature of air is lowered using the principle of evaporative cooling. This is the same principle the human body cools itself. Perspiration, sweat secreted by the body evaporates to cool the body.
Bees cool their hives by the same process as desert coolers. Bees fill in the hives with water and then fan their wings vigorously in front of it thereby evaporating the water. This cools the hives; the amount of water evaporated is controlled by the amount of air supplied by the wings. Imagine, a choir of bees masterfully choreographed by their conductor, where number of bees and the speed of the fanning controls the air flow, thereby controlling the hive temperature. Desert coolers need a fan with motor, a pump to discharge water from the cooler reservoir and a speed control for regulating the fan speed.
I could not help but bring out this similarity. Whole my childhood; I have spent countless summer days and nights in the cool dessert air. The bees were around much earlier than even human progression to Stone Age; and yet they were the masters of this technology that humans could invent only in early 20th century. However, the human ingenuity comes from the fact, the desert coolers come with naturally fragrant grass pads for the water absorption, which not only cools the air, it refreshes with pleasant fragrance too.