Grindal Worms


Grindal worms are similar to white worms, but are only about 1/3 the size. They are a great transition food for tropical fish fry when they get to the size that they need to eat a lot of baby brine shrimp to get full but are too small for white worms. 

Unlike white worms, Grindal worms like it warmer and a little moister.  My favorite containers are about 4” X 4” X 2” tall.  They are plastic containers left over from potato salad and coleslaw from the deli section of the grocery store.  I poke small holes in the top for ventilation.  

The culture medium is a 50-50 mixture of commercial potting soil and peat moss.  It should be kept pretty moist, almost a thick mud. Squeezing a ball of it should produce a few drops of water. Place about 1” thick layer on the bottom of the container and add your starter culture. The worms grow fast, and you can start harvesting in a couple of weeks.  

Grindal worm culture.  The white areas are masses of Grindal worms.

Grindal worms like it warm.  If you can’t keep white worms because of the heat, give Grindals a try.  I keep mine in an incubator I made for killifish eggs. It is made out of a Styrofoam cooler and a modified aquarium heater. The incubator keeps the temperature at about 75F.  During the summer my basement will reach 80F during long heat spells, and the worms don’t seem to mind.  If you don’t have something like an incubator and your fish room is cool, just place the container on top of a warm fish tank.  

Feeding is simple.  Just sprinkle food a little bit over the top. I commonly use Gerber multi-grain baby cereal, ground dry cat food and old fish food flakes.  The last two are higher in protein and cause the culture to produce more. Only feed enough to last a day.   

The worms will be on the top of the medium. When they are thick enough you can sort of scrape them off with a large tweezers and dump in the aquarium.  Collect the worms you are going to use before feeding for the day.  

One problem with Grindal worms is that they sometimes get a mite infestation.  If you look at the culture under a magnifying glass you can see small white or brown mites moving around on the surface. A few mites don’t cause too much problem, but if it gets too bad the culture will suffer.  

At that point the only thing you can do is to start a new culture.  Collect as many worms as you can, and place in a jar of water.  Let is sit for about 15 minutes. The mites will float and the worms sink. Pour off the water and start a new culture. Try to put it in a different location to minimize the risk of re-infection.  

Cultures last about 6 months.  After 4-5 months it is best to start a new one. Try to keep a couple of cultures just in case one goes bad.

© 2009 - 2022 Gary C. Sutcliffe


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