In nature, small gross things like nothing more than to live inside of larger gross things.
In this case, we have the mermithid nematode, a parasite that lives inside of spiders. Some sociopath killed filmed a large spider that he had just killed and caught this parasite growing gigantic as it leaves the spider. So yes, all those sci-fi movies you saw and complained about the bad cgi in, well, they’re looking pretty realistic now. If you were wondering where that parasite is going after leaving the spider, the answer is it has go lay eggs in your dreams.