Composting in Schools

Troubleshooting Worm Bins

by Jen Fong and Paula Hewitt

Fruit Flies

Though fruit flies do not pose any health hazards, these little creatures can be a nuisance in the classroom. To help prevent these potentially prolific pests, do the following:

1. Avoid putting rotting or rotten food in your worm bin. Fly larvae are more likely to be present on rotten food.

2. Cut food scraps into small pieces. Worms will be able to eat smaller pieces more quickly, thereby limiting the possibility of fruit flies thriving on decomposing food.

3. Don't overfeed worms. Ripe food that sits around in the bin attracts (and may contain) flies.

4. Bury food. Burying the food will help keep unwanted pests and pets from intruding on your bin.

5. Keep bedding material moist, but not too wet. Overly wet conditions encourage the proliferation of fruit flies. Wet conditions might also cause an odor problem, as anaerobic bacteria thrive when it is too wet.

6. Feed worms a varied diet. If citric foods dominate the bin, the bin may become too acidic, which may attract fruit flies.

7. Loosely place a piece of plastic or a sheet of newspaper inside the bin on top of the worm bin contents. This plastic or newspaper cover will create another barrier to help prevent flies from getting in (or out) of the bin.

8. Limit citrus fruits.

To help control an existing fruit fly problem, try the following:

1. Remove rotten food from the bin when fruit flies are present. Fruit flies often lay their eggs on decomposing food.

2. Tape or staple flypaper strips on the inside of the bin lid, and/or hang a strip near the bin. Flypaper strips can be purchased cheaply at most hardware stores.

3. Create a fly trap to put in the bin. A bowl of apple cider vinegar with a drop of dish detergent, placed near the bin, will attract and kill flies. Change liquid regularly to keep fly trap potent.

4. Place a whole sheet of newspaper on top of bin contents. Change this sheet regularly as flies tend to congregate on the newspaper.

5. Sprinkle lime in the bin to neutralize excessively acidic conditions.

6. For temporary relief, take bin outside and leave uncovered for up to four hours to air out the bin (out of direct sunlight).

If the problem cannot be controlled, have your class analyze the problem, and speculate about what is causing it. The best solution may be to harvest the worms and start a new bin from scratch, using what you have learned from your past experience to create a better bin.

Odor Problem

If your worm bin has an unpleasant odor, one of the following may be the culprit:

1. Bin is too wet. Solve the problem by not adding any water or foods with a high percentage of water (e.g., melons) and by adding more dry bedding.

2. Bin does not get enough air. Anaerobic bacteria (bacteria which thrive without air) is smelly. To aerate, add fresh bedding and mix bin contents daily.

3. The food in bin is naturally smelly. For instance, we have found that onions and broccoli do not smell very pleasant when they decompose in the worm bin. Simply remove any food source that smells bad from the bin.

4. Bin contains non-compostables. Meat, bones, dairy and oily products should not be fed to the worms because these items become rancid when decomposing.

Worm Death

If you notice the worm population dwindling, or worms crawling all over the bin trying to escape, check for the following:

1. Bin is too wet and worms are drowning.

2. Bin is too dry and worms dry out.

3. Bin does not get enough air and worms suffocate.

4. Worms do not get enough food. Once the worms devour all of their food and newspaper bedding, they will start to eat their own castings which are poisonous to them. TIME TO HARVEST

5. The bin is exposed to extreme temperatures. The worms thrive in temperatures from 55 to 77 degrees F.

NOTE: Dead worms decompose rather quickly. If you do not monitor the above conditions you can have a dead box of worms before you even realize it.

©Jen Fong and Paula Hewitt


Science &

in Schools


Cornell Waste Management Institute © 1996
Department of Crop and Soil Sciences
Bradfield Hall, Cornell University
Ithaca, NY 14853