Microworms are very small nematodes, less than 0.1″ long. Micro Worms generally live 20- 25 days and at three days of age, produce about 40 live young a day. Micro worms stay suspended in the water for an hour before settling on the tank bottom. They are a good first food for betta fry because they wiggle and the movement attracts the fry.
To make a microworm culture I sprinkle some instant mashed potatoes in a small bowl and add warm water to make a soft but not sloppy mixture. I add a 1/2 tsp of yeast to the culture for the microworms to eat (careful, yeast gives off CO2 and too much can kill the microworms. I also add a 1/2 tsp of sugar for the yeast to eat. After mixing the potatoes, yeast and sugar, I put the culture medium in clear 1 pint deli containers with tiny holes in the lid to let the CO2 out. (do not make the holes large enough to let fruit flies in). Cover the container about 3/8″ deep and add a tablespoon of microworms and culture medium from your old culture. If you don’t have an old culture, have a fish frind with a good culture mail you a tablespoon of starter in a ziplock bag in a standard legal envelope. After a couple of days, check the status of your culture by holding it up to the overhead light. If you see a shimmering movement on top of your culture, you have live worms moving about. After a few more days, you will have microworms crawling up the container sides, where they may be collected.
Microworms produce water and will eventually make a sloppy mess of the culture. If your culture becomes very watery add a piece of bread to absorb the water. Once you have a going culture, give some to neighboring fish keepers so that if your culture crashes, you can get a start back from them. Start a new culture every 2-3 weeks. If your culture starts to stink, start a new culture using worms from the sides of the old culture. If your culture crashes start a new culture with a bit of the old dead culture, almost always a few worms survive.
To harvest microworms, I use a small watercolor paintbrush. I swipe the sides of the container to gather them up and swish the paint brush in the fry tank. Microworms will only survive for 24 hours in water and any uneaten worms will decay and foul the tank. If you don’t keep snails in your fry tank, syphon the uneaten worms off the bottom daily before your next feeding.