The moisture, darkness and fermenting materials in a worm bin attract more than just their officially approved inhabitants, namely, compost worms such red wigglers (Eisenia fetida). Worm bins, closed systems containing bedding materials and kitchen scraps, can become a zoo of tiny living things. These range from bacteria and other microbes helping the worms to create compost to insects, which may not always be a welcome part of your mini-ecosystem.
These insects, about a third the size of a housefly and with red eyes, may end up in a worm bin via banana peels that haven't been washed and then frozen to eliminate their larvae. Keep about 4 inches of shredded moist newspaper on top of your bin bedding to make it difficult for female fruit flies to lay eggs in the food, advise Bob and Jan Ingram of the Trinity Ranch commercial worm farm in House Springs, Missouri. You can set bait traps for fruit flies by placing an inch of apple cider vinegar in soda bottles, adding a drop or two of liquid detergent to break the liquid's surface tension, drilling four, 1/8-inch holes in the lids and placing the bottles in and around the bin.
As their name implies, mites are tiny, about 1/50 of an inch long, such that some can barely be seen by the naked eye while others are microscopic. They have eight jointed appendages. While most mites are not likely to be harmful to your worm bin, they do signal that conditions are less than optimal for the worms. Either the bedding is too wet, you are overfeeding your worms or you're giving them wet feed, such as pulp from juicing or blenderized waste. Reduce a mite population by uncovering the worm bin and exposing it to sunlight to let it dry a bit. Reduce the amount of feed and add handfuls of dry bedding. Place pieces of cantaloupe, watermelon or potato on top of the worm bedding. Mites will accumulate on them, and you can remove the bait and drop it in water or bury it.
Compost and springtails, a small wingless insect about the same size as a mite, go hand and hand. They jump via a small spring-like structure under the belly when touched, hence their name. These insects come in many colors, from white, yellow and gray to red, orange, green and lavender. Springtails benefit the production of soil humus and don't really do any harm to a worm bin, according to the authors of "The Worm Bin." If you think they look unsightly, you can remove springtails using a handheld vacuum, the book advises.