caterpillar
Explanation
The Joke
A caterpillar asks a beetle, "Hey, Beetle. Can I borrow one hundred bucks? I'll pay you back double next month." The beetle cheerfully agrees: "Sure thing, Caterpillar." The next panel reads "6 weeks later..." and shows a butterfly flying away laughing ("heh heh heh") while the beetle sits on the ground, having been completely scammed.
The joke hinges on the biological fact that caterpillars undergo metamorphosis and transform into butterflies. The caterpillar took out a loan knowing full well that by the time repayment was due, it would have transformed into an entirely different-looking creature -- a butterfly -- making it essentially unrecognizable and able to skip out on the debt. It is the insect equivalent of taking a loan and then getting plastic surgery and a new identity.
The Humor
The comedy comes from applying a very human con (borrowing money with no intention of repaying) to the insect world, where metamorphosis provides a natural and foolproof escape plan. The beetle has no recourse because the caterpillar literally no longer exists in its original form. The butterfly's gleeful "heh heh heh" as it flies away confirms that this was always the plan, turning a beautiful natural process into a grift. There is also something inherently funny about the idea that metamorphosis, usually presented as a wondrous miracle of nature, could be exploited for petty financial fraud.