D&D Monsters: Giant and Phase Spiders

The first edition of AD&D includes a number of giant invertebrates, mostly insects. The idea behind these may be influenced by the "big bug" films of the post-WWII era, starting with Them! in 1954, and they provide the possibility of exotic-looking monsters that nonetheless have to look no further than the natural world for inspiration. 

Once we leave insects and look at spiders, there is an even more obvious inspiration: Shelob in Lord of the Rings. While she, and her relatives in other Tolkien works, were likely the primary inspiration behind the original giant spiders of D&D, there are plenty of other fictional examples. The cinematic classic The Giant Spider Invasion is one such (yes, I've actually seen it; there's 80+ minutes of my life I'm not getting back...) and, from more modern fiction, there's Aragog in the Harry Potter books. Giant spiders aren't found in European myth, but there are the Tsuchi-gumo of Japan, which are usually described as spiders (but sometimes crickets) and, at a stretch, Anansi the spider-god of West Africa.

D&D Monsters: Unicorns

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Unicorns are probably one of the best-known mythological creatures of medieval Europe, perhaps on a par even with dragons. Their origins are likely earlier than this, with the general concept of "one-horned magical beast" going back to at least the Ancient Greeks and having counterparts in other cultures, too. Some of these were aggressively dangerous, but it's the medieval version, appearing in religious bestiaries as an object lesson in virtuous purity that we're most familiar with and that forms the basis of the D&D creature. 

So iconic is the appearance of the unicorn that it's one of the few creatures in D&D that looks pretty much the same in every edition, regardless of artist, and that closely follows its traditional form. Early medieval unicorns weren't necessarily white, and some looked more like a goat than a horse, but such variations have long since vanished from the public mind. Pretty much everyone knows what a unicorn is, and what it looks like.