The Tsuchigumo are literally "earth spiders". In Japanese mythology, Tsuchigumo were spider-limbed monsters. Tsuchigumo were evidently based on one of the groups of people inhabiting Japan.
"Monsters said to come from the bastardization of certain clans of Japan. The word comes from a different word, "tsuchigomori", meaning dirt-dweller. Those who did not pledge allegiance to the Imperial Court were called this because they lived in holes and caves. As time passed, people may have misinterpreted the name for a literal meaning and made them into spiders, or perhaps the manifestations of grudges of those who were put to death by the Imperial Court."
—Shin Megami Tensei IV Profile
A Tsuchigumo is summoned by one of the Ashura-kai men in front of the elevator that leads to the Counter-Demon Force Base at Kagsumigaseki. The spider demon's defeat leads the men who summoned it to flee.
Devil Summoner: Raidou Kuzunoha vs. The Soulless Army
"A wild god shaped like a giant spider, which was said to have lived in Mt. Katsuragi. Originally a native of the land who lived in a hole after its tribe was defeated by the Imperial Court."
—Shin Megami Tensei: Devil Summoner: Raidou Kuzunoha vs The Soulless Army Devil Chart
A Tsuchigumo kidnaps Rin in order to distract Raidou Kuzunoha the XIV. Raidou travels to the Dark Realm and fights three Tsuchigumo to save her. This is the first boss fight in the game.
DemiKids: Light/Dark Version
"A demon that resembles a spider. Said to have a human face on its underside."