Totally depends! Let's look at some of the factors.
The Potential
Red Wigglers are capable of eating half their weight each day. European Nightcrawlers are in that same ballpark.
So, if you had an 18 gallon bin with 2 pounds of worms in it, theoretically they could eat a pound a day - approximately 10 banana peels. Which is pretty crazy because they can do that every day.
African Nightcrawlers can eat their weight and a half each day. So 2 pounds of African Nightcrawlers in an 18 gallon bin could eat 3 pounds of food a day - approximately 30 banana peels.
Imagine putting 30 banana peels into an 18 gallon bin and having it disappear overnight!
The Factors
Do worms always eat that quickly? No.
Several factors are in play when it comes to the appetite of the worms.
What food are they eating? How decomposed is it? Is the bin aerobic? How easily can they take a bite of it? How nutrient dense is it? How much of it is water weight? What temperature is their bin? Is the bin water-logged?
Foods like watermelon, or finished compost worms will eat extremely quickly. This is because they decompose rapidly/have already decomposed significantly. Its also very easy for worms to chomp down on these foods and fit them into their mouths.
Foods like cardboard and leaves are not as nutrient dense as other foods so they do not decompose as quickly and worms won’t prioritize them over other nutrient dense foods.
Basics of Max Food Consumption
The biggest factor above all is making sure the bin is aerobic. This will affect how quickly they eat more than any other factor. You should have plenty of bedding that keeps moisture at a good balance, and allows for airflow (airflow will also be created by worms if the contents of the bin are soft enough for them to burrow into it). Worms will not touch food that has gone anaerobic. Anaerobic material creates toxic compounds, bad smells, attracts pests, and can kill worms.
How to Feed and Manage Moisture
Overfeeding and overwatering go hand in hand. A lot of fruit waste/food scraps have a high moisture content. When you feed high moisture foods, you need to make sure you balance it with moisture absorbent bedding to keep the bin at optimum moisture.
Make sure when you add food that you place it where worms can get to it. Food scraps should be lightly buried - just enough so that it is covered by half an inch or so. Worms don’t like crawling up and out of the dirt to get to their food. Put it right on their dinner table!
Some foods, such as finished compost, don’t need to be buried. A worm bin cover will also help encourage worms to the top layer of the bin to feed.
It is also important to not overfeed in general. If you feed more than the worms can handle, other critters (things like fruit flies) will get to the food before your worms can. The general rule of thumb is to add your next batch of food as the last batch has mostly been eaten - say about 80% or so.
Conclusion
Worms have the potential to eat extremely rapidly. As long as you keep the bin aerobic and at proper moisture and temperature levels, no matter what you feed them you should see disappear pretty quickly.
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