Puddle Hermit

From the introduction: A Puddle Hermit is a fat, bloated breed of arachnid found throughout the Cannibal Sector, but most commonly located in the Lennox Territories. It is known to crouch for days at the water’s edge, gradually absorbing small quantities of stagnant water from puddles and lakes, storing the fluid inside a bulbous sac within its abdomen. Over time the Puddle Hermit converts these contents into a highly corrosive acid, which grows stronger the longer it is allowed to ferment.