My oldest child asked me why spiders curl up when they die, so we looked it up.
We found a web page with a lot of information about spiders, but it seemed a little too technical and wordy for casual curiosity… so here’s my simplified explanation:
Two of the six joints in a spider’s leg are hydraulic. The spider flexes muscles that increase pressure and straighten those joints. When the spider dies, those muscles relax and the legs curl up.
Here’s the photo (from a previous post) that inspired the question: