As a caterpillar, Wormy is a light shade of green with black eyes and white spots.
As a butterfly, Wormy is dark orange with black stripes and black on the outermost parts of his wings; this design is that of a monarch butterfly.
At some point, Sandy bought or found him in Texas. Sometime later, she took Wormy to her home in Bikini Bottom.
He later turns into a butterfly overnight.
Role in series
When SpongeBob and Patrick are pet sitting for Sandy, they and Wormy play games such as hide-and-seek and tag. However, overnight, Wormy quickly metamorphoses into a butterfly. SpongeBob and Patrick return but naively believe the butterfly ate Wormy when in reality it was Wormy. To save the town, SpongeBob and Patrick cause mass panic throughout and spread the news about Wormy all over town, all because of a butterfly that looks like a monster.
After Sandy returns from her trip and captures Wormy in a jar, the Bikini Bottomites celebrate, prompting Sandy to believe it was just because they missed her that much and she should leave town more often.
"Goons on the Moon"
Wormy is seen flying in space among asteroids and other pieces of junk.
In The SpongeBob Movie: Sponge Out of Water, a poster of Wormy in his butterfly form can briefly be seen in Sandy's treedome. The image of Wormy on the poster looks very similar to the one seen on the "Beware" fliers made by SpongeBob and Patrick.
The close-up shot of Wormy in his butterfly form is actually live-action footage of a buzzing horsefly (more specifically that of a notch-horned cleg fly).
This footage is royalty-free, and owned by Oxford Scientific Films. It can be found on Getty Images.
When Wormy's close-up is shown, the horsefly is making buzzing sounds, even though butterflies aren't buzzing insects.
The episode "Wormy" was banned in some countries because of Wormy's close-up shots scaring younger viewers.
The word "wormy" means infested or eaten by worms.
Even though Wormy is a monarch butterfly, his caterpillar stage does not look like a monarch caterpillar and instead resembles a typical green cartoon worm. During his live-action transformation, a monarch caterpillar is shown tinted green, as monarch caterpillars are yellow with black-and-white stripes.
The live-action footage used during Wormy's metamorphosis and the newscast depicts a female monarch butterfly with thicker black wing veins, as opposed to male Monarchs having thinner wing veins.