I just don't know what they are good for
What can you do with spider eyes in Minecraft?
DENNIS
You can eats spider eyes and will fill 1 hunger bar but will at the same time poison you. Craft spider eyes into fermented spider eyes and can be used for brewing.
Charlie
Spider Eyes are the base ingredient for the Mundane Potion. From this base potion, you can make all sorts of things like Potions of Swiftness, Healing, and Regeneration. See this image for more information: 
You can also eat Spider Eyes, but it'll probably poison you.
Bb Major
In vanilla (basic) Minecraft you can eat spider eyes, which isn't a good idea unless you are dying of hunger, or you can use them as a potion ingredient.
A number of magic related mods use them as well for various things, but that depends on the mod.
Thomas S