"Butterfly and the Bog Beast" is the fifth episode of season two and the eighteenth episode overall of the animated children's series The Magic School Bus. It originally aired on November 5th, 1995.
The class is playing in the biggest soccer game of the year, but they don't have a mascot. Dorothy Ann decides to use broccoli since it's a healthy vegetable. But Carlos rejects this, saying that the team can't be called "The Broccolis". Wanda wants to use the old mascot. But Tim reminds her that "it's so old no one knows what it is anymore." When moths fly out of it, Tim attempts to swat it. But Phoebe squelches his attempt and informs that moths are over 100,000 different kinds of moths than butterflies, adding that there are eight kinds of different moths than butterflies according to her book of butterflies and moths. As the class continues to try to decide on one, Phoebe suggests they name the team the Butterflies. She's immediately shot down by everyone but Arnold. Phoebe says butterflies are full of surprises, to which Carlos questions, as does Janet, who suddenly shows up. She brings everyone to her side when she reveals the game is against Phoebe's old team, the Bulldogs, and she suggests they name the team the Bog Beasts. All but Arnold love it; he questions what a bog beast is. Ms. Frizzle appears, and asks the class what a bog beats is. Dorothy informs that a bog is wet like a swamp, prompting Ms. Frizzle to take the class, plus Janet, on a field trip to Butterfly Bog.
During the bus ride, Phoebe asks Ms. Frizzle if the swamp has butterflies, to which Ms. Frizzle responds that the swamp has "all sorts of surprises". The Magic School Bus transforms to a boat and the bus rides through the swamp of butterfly bog. When a number of butterflies fly out of nowhere, Wanda says that she thought they were flowers. Ms. Frizzle states that looks can be deceiving. Some blue jays then swoop down to eat some of the butterflies and Janet compares it to the mascot that would be a butterfly to what the Bulldogs would do to it. Carlos learns that every animal can spot them due to their pretty colors. When a butterfly lands on Phoebe's finger, the rest of the class wonder why a butterfly stays beautiful. Janet attempts to use a net to catch it and the net ends up on Arnold's head.
Once the class makes it to the land, Dorothy tells the class that the best way to catch a bog beast is to use a bait. Janet jumps out of The Magic School Boat to go look for butterflies to use as bog beast bait, with Liz tagging along. Phoebe tries to shrink her with the Shrinkoscope, but the beam reflects off of Liz's costume and hits The Magic School Boat, shrinking it with the class. As Phoebe goes to try and stop Janet, despite being shrunk, the rest of the class follow her and Phoebe comes across a swallowtail caterpillar who is nearly five times her size.
Ralphie is convinced that the caterpillar is a bog beast. But Ms. Frizzle tells him otherwise, explaining that he has never seen a bog beast. The class then learn what it is and follow it, only to come across a Praying Mantis. They watch in delight as the caterpillar scares away the Praying Mantis and Carlos learns that this is called tricking the enemy by pretending to be something they're not. When Dorothy comes across a swallowtail caterpillar in her book, Wanda decides to name the school team that. Ralphie rejects this, claiming that the team will just get laughed at in the game. Ms. Frizzle tells Ralphie that caterpillars are tougher than he knows and Phoebe then learns that if a caterpillar keeps feeding itself, it will turn into a cocoon and transform into a butterfly as well.
Just then, the class notice Janet attempting to catch the butterfly and watch as she struggles to catch the flying insect. The class then notice that the butterfly uses its wings to disappear out of sight so that Janet can't see it against the log. Phoebe watches in horror when the butterfly finally appears in Janet's view as the latter attempts to catch it. Janet swings the net and knocks Liz into the mud, the impact causing the mud to fly on The Magic School Jeep. Janet brings Liz along with her to continue chasing after the butterfly.
Arnold attempts to unshrink him and the class to avoid being stepped on by Janet and a ringing sound comes on. Ms. Frizzle calls it "the Doo-Dinger", which dings when the port-a-shrinker is too wet to work, meaning that the class is stuck being small until the port-a-shrinker dries out. So Arnold uses the hairdryer Ms. Frizzle offers him and Ralphie accuses Phoebe for the predicament. Phoebe is finally fed up with being rejected about her choice of butterflies as the mascot and berates her classmates for turning against her and siding with Janet, and Ralphie for being selfish. When the class hear Janet's scream, they run out of The Magic School Jeep and come across a zebra butterfly. They then learn that butterflies trick, hide from, and scare their enemies for survival. Ralphie, however, still refuses to call the class team "The Walker Elementary School Butterflies". The class come to what appears to be a bog beast, but is really a butterfly with spots shaped as eyes to fool the enemies. Ms. Frizzle arrives and the class finally acknowledge the fact that butterflies are new, exciting, and surprising. So they agree to call their team "The Butterflies", even Ralphie who finally gives up being tough, and hop onto the bus. Ms. Frizzle transforms The Magic School Bus into a butterfly and The Magic School Butterfly flies off. Janet takes a glimpse of this and attempts to catch it, thinking that it's a real butterfly much to the class' horror.
The class asks Ms. Frizzle to do something. But Ms. Frizzle tells them that the port-a-shrinker is still wet. The Magic School Butterfly flies away, with Janet chasing after. When Ms. Frizzle reminds the class "When you're a butterfly, do as the butterflies do", Phoebe comes up with an idea. She uses the camouflage switch to transform The Magic School Butterfly' wings into leaves so that it would blend in with the leaves on the tree of a branch. Janet loses sight of it, but not when Arnold pulls the lever (thinking the port-a-shrinker is dry and Tim was too late to point out that it isn't dry), turning on the Doo-Dinger as Janet finally catches The Magic School Butterfly she thinks is a real butterfly. Phoebe uses one of the buttons to changes the wings colors into red, yellow, orange, and blue and gives them eyes as well. Janet takes a look at this and gets so scared she falls backwards into a mud puddle. Arnold ends up hitting the lever to transform The Magic School Bus, along with the others, into their normal size. Janet tells them what happens and finally learns that the "Bog Beast" she almost caught was a butterfly. Phoebe then states that the school team should be named "The Walker Elementary School Bog Beast Butterflies", which Janet finally agrees to.
During the soccer game, Janet is the mascot dressed as a butterfly that resembles a bog beast and Phoebe scores the winning goal for the team. The other team cheers for Phoebe, and Ms. Frizzle states that "there's no surprise like butterflies".
- During the producer's segment, Janet's character is described as "insensitive and inappropriate."
- This is Janet's second appearance.
- Goof: When Phoebe, Tim and Ralphie say "Janet's gonna feed us to the Bog Beast!", Ralphie's mouth isn't moving although his voice can clearly be heard.
- This is the first and only episode Janet is seen without her glasses
- Arnold reveals that Janet is his only cousin.
- Going by production order, this is the 3rd episode of Season 2.