xcX3v84RxoQ-4GxG32940ukFUIEgYdPy Spiders produce uric acid, which is a near-solid and excreted out white. This is done to minimize water loss. These malpighian tubules drain into an pouch attached to the digestive tract, or stercoral pocket. The uric acid waste from the is combined and eliminated together with solid waste from the digestive tract. In your spiders case, this would be undigested insect parts (black