Back before the new guano cards, batterflies would only eat 10 meat, even if you entered more in the quantity picker (e.g. you were aiming for 5, but got 55 or 555 instead...)
Players who tested found they would now consume more than 50c** / 80c of food (with upgrade cards 1 / 2 respectively) when given the opportunity.
** With the first card, 50c gets the same return as 100c, so the max useful feeding is 50c.