The Hour of the Gate — Alan Dean Foster

Accompanying the wizard Clothahump to try and mount a defense against the invasion of the monstrous insectoid Plated Folk, Jon-Tom and his otter companion Mudge find themselves faced with ever more serious obstacles-from an underground river that leads to the four waterfalls known as The Earth's Throat, to the spider-silk city of the wary Weavers and their horrifically attractive arachnid queen.