Longest
Get out your yardsticks! A 12-inch ruler won't be enough to measure the longest insects in the world, the walking sticks (order Phasmida). There are more than 3,000 species of these twiggy insects, and among them, a nearly 21.9-inch West Malaysian female Pharnacia serratipes wins for longest body length. She dethroned the previous record holder, a 21.5-inch Pharnacia kirbyi, who'd held the title for almost a century.
In case you're wondering what the longest centipede is, that title belongs to the Peruvian giant yellowleg, which feeds on mice, lizards, frogs and bats. But don't try to measure them; they may bite and their venom is toxic to humans.
Images: Top: Pharnacia serratipes stick insect, Wikipedia. Right: The stick insect Ctenomorpha chronus, Wikimedia Commons. Bottom: Peruvian giant yellowleg, Katka Nemcokova / Wikimedia Commons.