Like all insects, mealworms need moisture to thrive and reproduce. There is a lot of information on the web on this subject. In our years of breeding insects, we have tried every method of providing moisture. Adding water directly to the substrate will cause mold and kill your colony. We have developed several methods to successfully provide moisture to our mealworm colonies.
First, you can use a plain paper towel folded in half or quarters, add a little water and squeeze out the excess. Place the paper towel on top of the substrate. This can still cause mold. Therefore, you should leave the top of the mealworm tray. Check the mealworm colony frequently and make sure there is no mold. Now the best way to provide moisture is from sliced ​​vegetables. We have been using potato slices or whole carrots.
Mealworms get their moisture directly from the vegetables and receive nutritional value as well. In a few days all you need to do is dig through the substrate and remove the dried greens. In recent years we have discovered what we believe to be the best source of moisture out there.
The prickly pear (opunita streptacantha). We cut the nopal pads into strips and place them on top of the substrate. When the worms are gone, all that remains is the thin skin of the cactus. This species of cactus has few spines and the few that are can be easily removed with a knife. We have had absolutely no problems with mold and have found that the mealworm consumes the cacti before any other source of moisture. If you have access to nopal, we recommend trying it as a source of moisture for your mealworms.