To balance it you could instead make it take more than 1 bite say 2 or 3 preferably three before the enemy wakes up. But leaving it until the timer runs out for the paralysis would also work for pretty well. I think that the food pip should be thought over as it would prevent the slug spider from utilizing it's one thing that allows it to prosper. It's venom darts, the low spear damage makes it hard enough as it is to kill big creatures which would reward the most food to begin with so making it cost food would just be more of a curse than a blessing.