Culturing Mealworms

About Mealworms

With a little preparation, mealworms can be particularly useful as a rearing food for young, insectivorous finches. The worms are the larval form of the beetle Tenebrio molitor10 whose life cycle is divided into 4 stages: egg, larvae, pupae, and adult.

Life Cycle (at room temperature)
Egg 2-3 weeks to hatch
Larva 6-8 weeks
Pupa 2-3 weeks
Adult lays eggs in 2 weeks

The length of the life cycle is temperature dependent and ranges from about 5 weeks to about 2 months (with 2 months being more normal). Newly hatched mealworms are often too tiny to see; most finches prefer to eat those which are about ½" in size which is equivalent to a larval age of 4-6 weeks. Therefore, at room temperature, plan ahead for your culture to take 3 months to produce enough larvae for harvest.

Culture Set Up

You can follow step-by-step instructions to build a larger-scale Mealworm Farm External Site, or you can create a smaller set up at home as follows:

Container
Chose a container which is at least 15 cm deep with at least an 8cm gap between the medium and the top of the container:
    10 gallon tank
  • Any plastic container with lid should work (e.g. sweater box, disposable lasagna container, medium sized critter keeper, etc.)
  • A glass container such as a 10 gallon fish tank
  • A ventilated, tight-fitting lid over the container/tank will prevent any escapes (beetles are said to fly at night) as well as prevent any unwanted intruders.

Temperature, Humidity, & Lighting
  • Room temperature is best (Temperature range 15c-30c)
    If your mealworm cage requires heat support, purchase an under-tank reptile heating mat External Site under half of the enclosure. This provides a heating gradient. (You can even position two cages side-by-side, each sharing the same heat mat.)
  • 55-80% humidity, 70% ideal
  • Can be stored in a dark area or with day/night cycle.


Medium/Food
Insects for feeding insectivorous birds should be raised on high protein and calcium gut-loading supplements, because if they are fed on vegetable matter or bran alone, their protein and calcium content may be too low.7

Fill the bottom of the container about 1" (2.5cm) deep with your chosen medium:
  • Chicken starter without antibiotics/additives30
  • Bran* (insecticide-free) + oats + milk powder + crushed dog kibble
  • Bran* (insecticide-free) + ground-up Science Diet dry dog food + ground eggshell + Cheerios cereal + hulled sunflower seed kernels

*If using bran, freeze for at least 3 days or microwave first to kill any unwanted pests such as the Codling moth.41

The media has a shelf life ranging from 1 to 6 months and requires periodic replacement. Stir the media 1-2 times per week to prevent caking.

For mealworms fed on bran or an otherwise nutritionally poor diet, a gut-loading diet (consisting of unmedicated chicken starter with added 8% calcium carbonate, e.g. oyster shell flour External Site) should be fed for 1-2 days prior to feeding mealworms to birds in order to enhance the mealworms' nutritional value (see research abstract below). Moisture sources can include squash or pumpkin, sweet potatoes, carrots, and/or kale (remember to wash off pesticides first).

Moisture
Mealworms and beetles require a moisture source in the enclosure. Chose any of the following (ideally organic, but minimally washed & peeled prior to use):
  • Sliced carrot
  • Sliced raw potato, sweet potato, or yam
  • Kale
  • (Note that sliced apple tends to mold too quickly to be useful.)

Stick a tooth pick in each moisture source slice to facilitate later removal.
Place the moisture source(s) on top of a piece of cloth, paper, plastic, cardboard, or paper towels over the medium to prevent fouling of medium.
Change the moisture source every few days (sooner if it becomes dried out or moldy) to keep it fresh.

Substrate
When you notice that the worms are beginning to pupate, place a piece of crumpled and re-flattened paper over the substrate, and put a few moisture sources on top of it. This will allow for the escape of mutating worms so that once they are defenseless pupae, the other worms cannot devour them. Usually within about a week, the pupae will hatch into beetles.

Adding Mealworms
Mealworms may be advertised in different size classes, including mini, small, and giant; the mini & small (½" long) are most easily accepted by finches. They can be obtained online External Site, from some pet stores (especially those which Mealwormsspecialize in reptiles), or at tackle and bait stores. At brick-and-mortar stores, they are usually sold in small plastic containers that contain a little bran and about 50-100 worms. The containers are kept refrigerated to slow the mealworms' life cycle down into what is called "suspended animation." While refrigerated, these worms will not breed.

Purchase about 200 mealworms initially so that enough will survive to reproduce, and you'll have some extra worms to begin feeding your birds. Introduce the worms into the tank; once they begin to warm up, they will start moving around a lot more, and their life cycle will resume to its normal pace.

Maintenance
Remember hygiene is important even for insects. Build-up of frass (insect waste), dead bugs, moldy moisture sources, and too-high humidity in the container can all encourage growth of mold and attraction of pests such as mites and insects that may prey upon the mealworm colony.
  • Keep moisture sources fresh.
  • Clean container (removing dead bugs, shed skin, and frass) and replace with fresh medium regularly (once every 1-3 months).
  • If mite infestation occurs, individually rescue adult beetles & pupae to their own clean container to start a new culture; bake or microwave the contents of the infested container to kill the mites then discard contents outside (i.e. add to garden compost).
  • Bleach and rinse container before reuse.

Feeding Mealworms to Your Finches

Larvae shed their skin about once a week. For the first several minutes after they shed their skin, the larvae are white, and gradually become darker until they return to their normal golden-brown color. The best time to feed mealworms to your finches is while they are white in color, soft in body, and easy to eat. Mealworms retaining their hard, chitin body casing are relatively indigestible,8,30,26 but simmering in water for 5 minutes and chopping the mealworms into pieces are other ways to make the mealworms easier for a bird to consume.23 A good size for feeding to finches would be about a ½" long. Some finches such as the Chestnut-breasted Finch14 may prefer to eat the pupae instead of the larvae.

When mealworms make up a significant part of the diet, additional calcium must be added to bring the diet to the proper 2:1 calcium:phosphorus ratio.7

Serve live mealworms in a smooth-sided feeding dish as they will not be able to escape.

Tips

Refrigeration slows down metamorphosis; you can store pupae in the fridge until more adults are needed in your culture.

Mealworm Nutritional Value Research

J Zoo Wildl Med. 2000 Dec;31(4):512-7.
Increasing the calcium content of mealworms (Tenebrio molitor) to improve their nutritional value for bone mineralization of growing chicks.
Klasing KC, Thacker P, Lopez MA, Calvert CC.
Abstract
The purpose of these studies was to determine the husbandry variables that optimize the Ca content of mealworms (Tenebrio molitor) and to determine the bioavailability of this Ca for bone mineralization in chicks that consume the mealworms. To determine the optimal level of Ca in the substrates used in short-term (< 14 days) holding of mealworms and to determine the length of time that mealworms should be exposed to high-Ca substrates, mealworms were placed in either a wheat bran or a chicken starter substrate supplemented with 0, 4, 8, or 12% Ca from CaCO3. The mealworms were harvested after 0.5, 1, 2, 3, 4, 7, or 14 days. The Ca content of the mealworms was greatest with the use of chicken starter and increased linearly with the Ca content of the substrate. In general, the Ca content of the mealworms increased during the first 24 hr and decreased after > or = 1 wk, especially at the higher levels of Ca supplementation. The chicken starter also resulted in higher levels of vitamin D in mealworms. Mealworms held in wheat bran with 8% Ca were fed to growing chicks. Ca bioavailability was calculated from the chicks' bone ash. The Ca in these mealworms was 76% as bioavailable as the Ca in oyster shell.


Additional Resources Used for This Article:
Breeding Insects as Feeder Food External Site
Raising Live Foods (Complete Herp Care) External Site
Breeding Invertebrates for Food & Fun External Site
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