If You Never Eat

...why would you need mandibles strong enough to snap a pencil in half?

The Titan beetle (Titanus giganteus) is the longest known beetle in the Amazon rainforest and one of the longest insect species in the world. It is from the family Cerambycidae (longhorn beetles). The titan beetle is the only member of its own genus. It is known from the rain forests of Venezuela, Colombia, Ecuador, Peru, the Guianas, and north-central Brazil, where it is most commonly collected by the use of mercury-vapor lamps, to which the males are attracted. There is a local 'cottage industry' in French Guiana of leading tours specifically to collect specimens of this beetle (which can command prices over US$500), and other countries' ecotourism agencies mention these beetles in their advertisements.

Adults can grow up to 6.5 inches (16.7 cm) in length.[2] It is said that their mandibles can snap pencils in half and cut into human flesh. Adult titan beetles do not feed, they simply fly around to find mates. They are attracted to bright lights after dark. There is an extensive sequence towards the end of Sir David Attenborough's Life in the Undergrowth series (in the version released in the UK) which prominently features a hunt for this beetle. In it, an adult specimen was found by American entomologist, the late Frank Hovore (he died in 2006, very proud of finding Giganteus - http://www.unl.edu/museum/research/entomology/workers/FHovore.htm) and brought back to Oxford University. Because the adults do not eat, this specimen was cared for until it died.

The larvae have never been found, but are thought to feed inside wood and may take several years to reach full size before they pupate. Boreholes thought to be created by titan beetle larvae seem to fit a grub over two inches wide and perhaps as much as one foot long.