Redworm bins generally pretty much run themselves if you followed good practices in setting up your system. However, no matter your diligence, your attentiveness to detail, you still always should stay alert and be prepared for all circumstances. The good thing is that if you do come across any problems that you can't resolve on your own, you can come here and possibly find the solution to your problem. Let me go over a few of the pests you may encounter in your vermicomposting system and I will also try to provide you with some remedies, as well.
Let's talk about fruit flies, first. Prevention is the key, but if that isn't always possible, there are other approaches I will talk about here.
Fruit fly eggs are laid on the surface of fruit and vegetable peels and scrubbing the produce will help get rid of them. You can also microwave your food scraps for 5-10 minutes or you can freeze the scraps before placing it in the worm bin. That should destroy any eggs. Make sure to let the scraps come back down to room temperature before adding it to your bin.
If you are unable to resolve the problem before the fruit flies make it to the bin, there are ways to get rid of the fruit flies. One thing you can do is get a wide-mouth jar and put about an inch of apple or red wine vinegar with a drop of dish soap in the jar. Then, take a piece of stiff paper and roll it into a funnel and insert it into the jar. Don't let the end of the funnel touch the vinegar at the bottom of the jar. Another way to deter fruit flies is put a venus fly trap near your bin. There is also a predatory mite, Hypodspis miles that will eat gnats and fly larvae. There is a predatory menatode, Steinernema sp. that will kill fruit fly larvae.
How to Make a Fruit Fly Trap For Under Two Dollars
You should always keep a layer of shredded newspaper or moist coir on the surface of your bin. This might serve to hinder emerging adults and hamper adults from laying their eggs. This will still allow air and moisture to circulate but baffle the annoying flies. You can also hang one of those sticky tape traps near your bin.
How to Make a Fruit Fly Trap
You can use Bacillus thuringiensis. It can be administered as a drench to help kill off the fruit fly larvae. You can also use Neem, which is an organic oil that you can purchase at a garden store. It's used to spray and control garden pests. You only want to use this in an extreme infestation as it can be harmful to the beneficial organisms in your bin. It will not harm your redworms. This is certainly not all of the available solutions to getting rid of fruit flies but it should help you to get a handle on the situation. With the internet available, I encourage you to do some additional research if these solutions don't work for you. Fruit flies are not harmful to your worms, just a pest.
As for mites, open up your bin and let the sunshine in for a few hours. You will also want to cut back on water and feed - and then every 1 to 3 days, add some calcium carbonate - you can also add some additional shredded paper or coconut coir to aborb excess moisture. Drain off any liquid. Make sure if you have a spigot on your bin, that it is not plugged.
Black Soldier Fly Larvae
This is another critter than can get to be a pain in the patootie but in small amounts is not really harmful to your redworms. However, if the Black Soldier Fly Larvae build up their numbers, watch out, as they generate a lot of heat with their vigorous munching and can overheat your bin and run your worms out of town. I pick the larvae out when I see them. I would suggest you do the same. There are people who do raise BSFL and I say that in the correct place with the person interested, they can be a great asset. So, don't write them off. If you want to learn more about BSFL, watch the videos here.
Black Soldier Fly Larvae in Worm Bin BSFL
BSF Larvae and Redworms Working Together
Do keep in mind this guy in the above video has a large outdoor system, where the redworms and Black Soldier Fly larvae have an easier time of keeping their own space - not so easy to do in a home worm bin, so I caution homeowners with small bins of keeping BSFL and redworms together.