Stinkfly is a Lepidopterran from the swamp planet Lepidopterra (a play on lepidoptera, the scientific name for butterflies and moths). Another of forms more commonly used.
Stinkfly is meant to be a combination of various Earth bugs (dragonflies, crickets, and preying mantises specifically). His primary ability is flight facilitated by the four thin wings on his back, which grant Stinkfly high mobility and speed. Stinkfly also possesses disproportionate strength, enough to carry people and objects heavier than himself. In "Don't Drink the Water", the child form of Stinkfly (Stinkyfly) was able to unleash a powerful herbicide gas by farting. Stinkfly's four eye stalks give him a wide range of vision from the sky, including the ability to look directly behind himself. Pollen ducts in his eyes and mouth allow Stinkfly to excrete high-pressure streams of liquids. The type of liquid can range from a flammable toxin to an immobilizing jelly. His razor-sharp tail and pincer-like legs can also be used in melee combat. Stinkfly's primary weakness is water, which can negate his flight if it gets on his wings. In addition, while his body is fairly strong, his wings are not. A more minor inconvenience is Stinkfly's intense body odor (hence the name), which is a result of the oils he secretes to keep his joints moving. Ben first transformed into Stinkfly in "Washington B.C." when he had to save Gwen after she fell from the Washington Monument.
In the future, Stinkfly's eyes are bigger, with visible pupils, the front legs are bigger, that resemble those of a mantis, and his stinger is larger and is white instead of black.
The 10-year-old Ben's Stinkfly made an appearance in the Ben 10: Ultimate Alien episode "The Forge of Creation". His eye color changed from orange to green, His hands are green instead of black, his teeth are white instead of green, and he shot lasers from his eyes instead of liquid. His Omnitrix badge also changed from white to green.
Why he's called STINKfly