HOW TO - Cultivate mealworms

Cultivate

mealworms by Mark Paterson

Mealworms are the larval stage of a black beetle (Tenebrio molitor) that is considered a pest as they commonly infest grain storage facilities, but they are an excellent live food for reptiles, fish, birds, and small insectivorous animals. Most pet shops stock them or they are easy and inexpensive to culture yourself supplying year-round food for your pets. As it can take a few months to establish good numbers from breeding, ensure that you start with enough to feed out as well as to breed from. The life cycle of the mealworm beetle starts with an egg which hatches into a larva, commonly known as a mealworm, and these feed on grain. After growing and moulting their exoskeleton several times the larvae transform into yellowy brown pupae which can’t eat or move much. After about 3 weeks the pupae metamorphose into beetles. At first the beetle is whitish with a soft shell

Mealworm larva Photo: AJC1

Mealworm pupa Photo: AJC1

Mealworm beetle Photo: Didier Descouens

which then darkens and hardens to dark brown/black after about 2–7 days. Mealworm beetles reproduce for a few months before dying. The duration of the life cycle is affected by the temperature they are kept at, while the optimum is around 20–25°C any cooler than that they slow down and hotter they can become sterile. Housing to keep them just requires a container that is not airtight. Cardboard or polystyrene boxes are no good as the worms will chew through them. Mealworms have been in the news recently as they have microbes in their guts which allow them to digest polystyrene. I use plastic or glass as

Mealworms in a container of bran Photo: Richard Chambers

they can easily climb out of a wooden box. Half fill the container with bran (at least 50 to 75mm). Cornmeal, oatmeal, or bran meal will all work. Then place a small culture of mealworms on top of the bran, add a couple of slices of carrot or raw potato and cover with a piece of cloth or a folded-up sheet of newspaper as larvae will accumulate in this making them easier to collect. It is important to not allow the culture to get damp as it can sour quickly and kill off the worms. When feeding out remember the larger the worm generally the harder its outside surface is. Just after each moult they are white and soft so are at their most digestible.

Having a clear container will let you see how much frass (waste) has accumulated so you can get an idea of when to change the bran. If the container doesn’t have a ventilated lid, drill holes in the plastic cover. If condensation forms on the inside of the lid, you need more holes. Good ventilation helps prevent mould growth and keeps the chance of a mite infestation low. Mites are tiny whitish eightlegged arachnids that look like sawdust. They can’t fly and they can come into your culture with your bran or with mealworms and are usually associated with excessive moisture in the box. Mites are rapid breeders and once they infect a colony it is best to start over. Give things a good clean out and look at putting a fine mesh screen top on the containers to protect the colonies from any further invasions. I use two or more containers: a top one with a mesh floor for the beetles, this allows any eggs laid by the beetles to fall through into a lower container which contains bran for hatching worms to feed on. I do this as the beetles can eat their eggs. Once I see small worms appearing in the lower container I move the adults to a new set up I have got ready. Like pretty much all living things, mealworms produce waste which builds up over time so keep your mealworm colony clean and healthy by removing any dried-out bits of vegetable and fruit and any dead mealworms or beetles. As the worms grow they shed their exoskeleton, and these can build up on

Two continer breeding setup Photo: Mark Paterson

Adult container with mesh for eggs to fall through Photo: Mark Paterson

the surface of the colony. I remove these by using a vacuum cleaner and holding it about 5 to 10 cm above the surface. If the set up starts to smell I usually sieve out all worms and move them to a new container with Bran. This allows me to disinfect the container and ready it for another round. I use a 50/50 mix of white vinegar and water to wash the container and then leave it to dry before reusing it. Mealworms can be stored in the refrigerator for up to 8 weeks. This will slow them down from developing and keep them for feeding later. Any mealworms left in the container will mature and become pupae, then beetles, so continue moving beetles to another container as they mature.

Reptiles

Remember mealworms are only as good a food for your animals to eat as the food that you feed them. If you are growing mealworms to feed to reptiles it can be worth adding extra supplements to make the mealworms fatter and healthier before feeding. Sprinkle supplements into the bedding or directly on the fruit used in the breeding container. Examples of supplements are calcium or mineral supplements, finely ground eggshell, wheat germ, whole wheat flour, and dry brewer's yeast (provides proteins). You can add slight moisture to the mealworms diet by placing thinly sliced