Beetles, members of the order Coleoptera, are the most diverse group in the animal kingdom, with the largest number of species. Over 350,000 species have been described by science, with estimates putting the total number of species between 5 and 8 million. About 25% of all known life-forms and 40% of described insect species are beetles.
These bugs are placed in phylum Arthropoda (arthropods), class Insecta (insects). Like other insects, they have a hard shell, open circulatory system, and are primarily small invertebrates. What distinguishes them from other insects is their hardened forewings, from which the order gets its name: coleo means shield and ptera means wing.
Once, the biologist JBS Haldane was asked if he could say anything about God from his study of nature. Haldane replied, "He must have an inordinate fondness for beetles." Discovering and classifying new ones is truly a challenge for biologists, and hundreds or thousands of new species are discovered every year, mostly in the tropical zone. When scientists leave out a net and shake trees in the tropics, thousands of the insects fall into the net. They may be the easiest order of animal to find new species within.
Beetles range wildly in size. The smallest known, Nanosella fungi, is 0.0098 inches (0.25 mm) in length with a weight of 0.4 mg. The largest, Titanus giganteus, exceeds 8 inches (20 cm) in size and weighs over 100 grams. They set other interesting records as well. For instance, the rhinoceros beetle species, Dynastes hercules, can lift 850 times its own weight, a record left unchallenged until it was discovered that the tropical mite, Archegozetes longisetosus, could lift 1,150 times its own weight. That's like an elephant that can carry 1,150 other elephants on its back.
Because of their abundance and diversity, beetles are popular subjects for insect collections. They are dried, mounted, and put on display in hundreds of thousands of public and private collections throughout the world. It is through their study that many of the early post-Darwin biologists came to understand evolution better.