Drider

Driders are a creature that originated in the Forgotten Realms of Dungeons & Dragons. They are basically Centaurs, but replace "human" with "drow elf" and "horse" with "giant spider". Basically, the batshit crazy Lolth has a history of transforming her followers into half-spider monsters for shits 'n' giggles.

Now, in the original lore, this was supposed to be a punishment for those drow who failed one of Lolth's various psycho-tests. Now, if you look at the fact that Lolth herself is basically half-drow and half-spider in her favorite avatars, and that she considers spiders sacred (her original title was Demon Queen of Spiders for chrissakes), and that driders are actually more powerful than the drow they were made from, this doesn't make a hell of a lot of sense. 4e took the rather sensible option of making this a cherished reward for her most worthy followers instead, though 5e went back to the old stupidness after one butthurt oldfag too many couldn't stop b'awwing about it, and Pathfinder made driders into the results of twisted mutative "fleshcrafting" done on failures with no divine connection at all.

Since the basic picture of a drider is inevitably a sexy black-skinned elf-lady atop a giant spider, centaur-style, it should be no surprise that driders have taken off as one of the more common forms of monstergirls. Non-explicitly D&D based ones tend to be called Arachnes, however, since, y'know, trademarks and Arachne being the woman who became the first spider in Greco-Roman myth and all.

It's surprisingly common for monstergirl driders to parasitically lay eggs inside of human hosts, especially nubile human or elfin maidens. Precisely why, nobody freaking knows, especially since spiders don't do that sort of shit in real life. Like, at all. That's a wasp thing, the eggs are usually injected like a syringe rather than deposited like a tube and as an ironically fun fact, spiders are known for being at the receiving end of it.