Parasites aren't limited to dogs, humans, and other animals you may be more familiar with. Even icky spiders and other creepy crawlies can be affected by parasites.
In this instance, a man who sprayed a spider with spider poison wasn't expecting to see a large parasitic worm spew out from the spider's body, but when the spider died, the parasite didn't have a live spider to snack on anymore.
As it turns out, these worms are parasites that eat these spiders inside out, starting with the least critical organs and working their way up in order to keep the spider alive as long as possible. These kinds of worms also affect other insects, such as crickets and praying mantises.
Spiders can contract a parasitic worm such as this one by eating their eggs, or eating another insect that has eaten the eggs. These eggs then hatch inside of the spider and attempt to lay more eggs to survive.