There are a lot of different types of worm bins that people use for vermiculture. You can build one or buy one, but they all have similar management techniques that you can employ to reduce odors and annoying flies. This is of particular concern when using food scraps as part of your feed stock or all of your feedstock. As anyone who has been on a picnic can attest, flies like food and they are incredibly irritating. They land on your food and eat by spitting their digestive juices out only to quickly mop up the the yummy nutrient sauce they created with their spongey mouth parts. They also like some types of food because it provides a wet place to lay eggs and a nutrient source for the young to get a good start. For our wormery, I’m fairly lucky to have pre composted horse manure to use as a feedstock. Whenever I have food scraps from the lunch room or a large event, I cover the thin layer of food scraps that I’ve spread out on the top of the worm bin with horse manure to prevent the flies from easily accessing the food. This keeps fly populations low and controls odors. If you do not have the horse manure, you can use worm castings from the bin to cover and bury the food scraps. Ideally, you want the food scraps layer to be shallow so that it doesn’t putrefy and create a lot of anaerobic activity because that is where the stinky smells come from. Flies are attracted to putrid smells and know there is good egg laying ahead whenever they find them. If you do not have horse manure or enough castings, consider some peat moss or coconut coir, or shredded card board/paper to get some coverage. When adding any of these materials to the bin, please try and balance out the extra carbon added to the system so your C:N ratios don’t get too out of whack. You essentially want enough to cover the food scraps and have a little dryness on top so as to discourage the flies from finding a nice place to raise a family.