Minecraft wiki entry for Survival_in_an_infinite_desert, associated text: Spider eyes can be eaten, but the net effects are usually worse than not eating them. The poison does more damage than the food value is worth. They are only worth eating if you are already badly injured down to around half a heart (so the poison damage has little or no effect). Still, since you are unlikely ever to be brewing potions, you may as well stockpile spider eyes for the most desperate of food emergencies.