Although commonly referred to as “worms”, microworms, banana worms, and walter worms are actually different species of harmless nematodes. They all belong to the Panagrellus genus- Panagrellus redivivus, Panagrellus nepenthicola, and Panagrellus silusioides, respectively. The main difference between them is size; otherwise, they all culture exactly the same way. Therefore, this blog will encompass all three species. They are all very tiny, but they differ slightly in that banana worms are the smallest, walter worms are the intermediate, and microworms are the biggest (all less than 3mm full grown). For the sake of simplicity, they will broadly be referred to as “microworms” from here on. Microworms are the perfect live food for many types of nano fish, baby axolotls, and fish fry. When added to water, they sink to the bottom and can survive for up to 24 hours, making them especially ideal for small bottom feeders such as Corydoras catfish fry. They are also very easy to culture and maintain so long as one remembers to re-culture them every few weeks.
After about a week, you should see the worms climbing the sides of the container. This is when you can harvest them. All you have to do is wipe the sides of the container with your finger or a clean paintbrush and dunk into either a collection cup of dechlorinated water or directly into the aquarium you are feeding. If harvesting more than one type of ""microworm"", try to keep all collection cups, brushes, etc. separate. Rinse off your finger between culture types if using your finger to harvest. If you can, adding active dry yeast a few hours or the night before harvesting can really get those nematodes climbing. You’ll want to add active dry yeast at least once or twice a week to feed the nematodes and keep production where you want it.
When the sweet yeasty smell a healthy culture gives off starts turning a bit sour, you may want to start new cultures. This could be as long as a month along in the culture’s age. If you wait even longer than that and the culture dries out, you’ll know you waited too long. It is usually best to start a new culture every 2-4 weeks to keep maximum production. It can be easy to forget, but you’ll want to stay on top of it, especially when raising fry. As with any live food, the more cultures you can maintain, the merrier. If you choose to work with all three Panagrellus species, you’ll just want to be careful when culturing to keep spoons separate and wash hands when switching between species to maintain their integrity.
Aquarium Wiki list of live foods for fish