Arachnocidal substance

 is an item in the.

Journal entry

 * [A card stuck to the bottle says "Arachnocidal Substance," but there's another, barely legible label underneath]
 * Condensed arachnomorph sex pheromones (female). Substance will cause irritation to the eyes and skin. If swallowed, immediately seek the care of your nearest leech. Do not use in enclosed spaces. Use: Half a quart of concentrate will effectively spread over 2 fiefs of land and can lure in between 4 and 5 male arachnomorphs.