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Keeping & Breeding Crickets As Feeder Insects

Feeder Mealworms

Feeder Mealworm Picture

Feeder Mealworm Introduction:

The so called "mealworms" are sometimes incorrectly classified as worms, when they are in fact the larval (pl. = larvae) stages of Tenebrio and Zophobas beetles. They are natural pests of flour, meal and other grain products, but are used in various ways such as food for man and animals, for research and as bait.

Both the larvae and the beetles can be used fresh or dried.

Fresh mealworm larvae can be fed to various animals such as lizards, amphibians, primates, fish, birds and bats. Dried mealworms are not only the ideal food for tropical fish, semi-aquatic amphibians, reptiles, birds, hedgehogs, lizard, iguanas and turtles, but can apparently also be used as a high protein source for livestock. Dried mealworm larvae can be used instead of nuts, raisins and chocolate chips in many cookies, bread, and dessert recipes. In powdered form, mealworm larvae can also replace part of the flour in cakes or pie crusts. Barely thawed, whole, or grounded mealworms can be added to sauces or used to make spreads.

Mealworm larvae can be bought from most specialized pet shops and some bait shops. In some countries larvae and beetles can be collected from feed, grain or meal in barns or feed storage rooms. Mealworms are relatively cheap in comparison with other life food. They are even commercially bred for human consumption in some countries! Larvae contain large percentages of fat and protein apparently making them extremely tasty. Because of the high fat content they should never be fed as a main part of any diet, especially for animals. Some pet animals might become addicted and will refuse to eat anything else!

Figure 1 a Common mealworm (Tenebrio molitor) larvae; b Common mealworm (Tenebrio molitor) beetle; c Common mealworm (Tenebrio molitor) pupa; d Giant mealworm (Zophobas morio) larvae (Photo not in scale); e Common mealworm (Tenebrio molitor) skin.

Feeder mealworms are most commonly available in the following sizes:

Standard mealworms (30 mm / 1.2 ")
Mini mealworms (10-15 mm / 0.4 - 0.6 ")
Giant mealworms (40-60 mm / 1.6-2.4 ")

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Feeder Mealworm Classification:

Kingdom
Animalia

Phylum
Arthropoda

Class
Insecta

Subclass
Pterygpta

Superorder
Endopterygota

Order
Coleoptera

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Feeder Mealworm Biology:

Zoology
Modern entomologists use the term Hexapoda (hex"sah-pod'ah - hexa meaning six) as a more inclusive class name. Hexapods (insects) are characterized by having three pairs of legs. Some have wings and the body is divided into a head, thorax and abdomen. Insecta is used as a more restricted term referring to hexapods whose mouthparts are more or less exposed. Mealworms belong to the Superorder Endopterygota (en-dop-ter-i-go'tah) meaning they have holometabola or complete metamorphosis and the wings develop in the pupal stages. The Order Coleoptera (ko-le-op'ter-ah) or beetles, is the largest insect order and includes insects with sclerotized forewings which form covers over the abdomen, membranous hind wings and chewing mouthparts.

Feeder Mealworm Life Cycle
Tenebrio and Zophobas beetles undergo holometabola or complete metamorphosis (change) during their life cycle (Figure 2). After metamorphosis the beetles mate and lay eggs, which hatch into larvae (singular = larva) or so called "mealworms". The larvae undergoes a series of moultings and pupate (forming pupae, sl. = pupa), which undergo metamorphosis and emerge as beetles again.

Feeder Mealworm Life Cycle Picture

Figure 2 Life basic cycle of Tenebrio & Zophobas beetles. Adult beetles mate & lay eggs, which hatch into larvae or the so called "mealworm". Larvae pupate & undergo complete or holometabolism & emerges as beetles.

Moulting & Exoskeletons
All insects, including mealworm beetles poses exoskeletons which consists of an inner, softer layer/membrane and an outer, harder layer. The outer membrane is also referred to as the skin. The exoskeleton supports the rest of the body and the internal organs. The exoskeleton consist of indigestible proteins and chitin, which becomes very hard when it is dried out. When the exoskeleton is hard, it is rigid and cannot bend or expand. This obviously prevents insects from growing. For insects to be able to grow, they need to shed or moult to get rid of the outer hard layer of the exoskeleton wherafter the softer inner layer will expand according to the new body proportions. The inner, which becomes the outer layer, will then dry out and harden to become the new outer protective layer.
Larvae are covered by a cuticle, which is also a layer consisting mainly out of indigestible proteins and chitin. Cuticles are indigestible, but not as hard as the exoskeleton of the beetles.

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Standard Or Common Feeder Mealworms:

These mealworms are larvae of the Common Darkling beetle (Tenebrio molitor). They are indigenous to temperate regions of Europe. Larvae measure about 30 mm/ 1.2 " in length. The colour of the beetles varies from light tan just after emergence from the pupae to a darker jet black after the exoskeleton has completely dried out.

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Giant Feeder Mealworms:

Giant mealworms (Zophobas morio) are sometimes wrongly referred to as Superworms. Superworms are apparently common mealworms (Tenebrio spp.) which are steroid enhanced. Giant mealworms are indigenous to the tropical region of Central and South America. Fully grown larvae measure 40 - 60 mm / 1.6 - 2.4 " in length. They live in rotting vegetation on forest floors and like warm damp conditions. Larvae bore into rotting wood and create pupation chambers.

In some countries such as Japan the beetles are kept as pets and are mainly fed fish flakes.

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Table 1 - Comparison of approximate nutritional composition between the giant mealworm (Zophobas morio), a & the standard mealworm (Tenebrio molitor), b:

Nutrient	Percentage (%) (a)	Percentage Dried (%) (b)
Moisture	61.4	3.0
Protein	20.0	56.6
Fat	14.3	28.2
Ash (minerals)	1.3	-
Other	5.2	-

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Basic Feeder Mealworm Keeping & Breeding:

Note: This section also applies to breeding standard mealworms & keeping & feeding both giant & standard mealworms as feeding stock

Both the Giant and Common mealworms are commercially available from most pet shops. They are sold by weight or number in small plastic containers. Before buying, inspect the container and determine which stage is present and/or make sure that the majority of the insects are still alive. When selecting breeding stock large worms or beetles are more desired. Because Giant mealworms need to be induced to breed, the beetles are usually not sold commercially for feeding purposes.

All stages thrive and breed at room temperature (24 - 27 ºC / 75 - 80 ºF) in dark dry conditions with just enough moisture. Below these temperatures colonies become inactive. Inactive larvae stay fresh for longer but no breeding or growing activity will take place. Lower temperatures are thus ideal for keeping food stock (mentioned below).

To house feeder mealworms, any shallow, smooth walled container will do. Lids are only necessary to keep unwanted spiders and insects out (when problematic). A well ventilated lid or screening, secured with a rubber band, can be used. Giant mealworms will eat and destroy wood containers and the beetles of both species will be able to climb any rough surfaced walls. Roughly about 5 000 larvae can kept in a 18 ℓ / 5 gal (US) container. The ADDIS™ 21 ℓ / 5.5 gal (US) (40 x 35 x 15 cm / 16 x 14 x 5.5 ") container (Fig. 3) is commercially available and should be adequate for breeding feeder mealworms. Smaller ADDIS™ 13 ℓ / 3.5 gal (US) (35 x 25 x 15 cm / 14 x 10 x 5.5 ") containers can be used for keeping feeder mealworms.

a	b
c	d
e	f

Figure 3 a ADDIS™ 21 ℓ / 5.5 gal (US) (40 x 35 x 15 cm / 16 x 14 x 5.5 ") container. This should be more than adequate for keeping & breeding feeder mealworms; b ADDIS™ 13 ℓ / 3.5 gal (US) (35 x 25 x 15 cm / 14 x 10 x 5.5 ") container which can be used for keeping large amounts of feeder mealworms; c Burlap used to make bags; d Burlap with a piece of sliced potato or potato peels inside a breeding box; e A nice & practical way to store more than one layer of mealworm containers are medical or so-called Q-cards; f Boar & sow meal fed for pigs is an easy obtainable, bulk, cheap alternative to bran can also be used as substrate. Boar & sow meal is available from co-operation or feeding companies.

The food and the bedding (or substrate) are usually the same for mealworms. A combination of bran or bran flakes and rolled oats or oatmeal can be the sole food supply for breeding stock. Both the mealworms and the beetles will eat the substrate. Substrate should be 2 to 5 cm / 1 to 2 " deep. Maize or corn meal, cricket chow, cat/dog food, fish flakes (especially for giant mealworms), non-fat or skimmed milk or crushed bran flake cereal, bone meal or fine mouse cubes are added from time to time to make the food more balanced. The addition of extra foodstuffs can be used as a means of gut loading.

Vegetables such as carrots, overripe banana peals, pieces of ripe apple, half sliced oranges, potatoes or potato peals and celery should be added on top of the bedding for extra gut loading or to supply moisture. Powdered minerals mixed with bedding are also popular. Vegetables needs to be replaced regularly or when they become spoiled or moulded. Gut loading should take place at least two days before feeding to other animals.

The substrate should always be dry. Excessive moist will lead to substrate moulding and subsequent death of the mealworms. Ventilation is very important and aids in the maintenance of a dry environment.

Some people also recommend placing layers of moist burlap (a strongly woven cloth used to make bags - Fig. 3 c & d) and pieces of newspaper on top of the bedding with fruit and vegetables on top.

On arrival, standard mealworms should be removed from the small tub in which they were bought and transferred to a larger container with bedding (including gut loading elements). Containers with mealworms can be stored at temperatures between 12 and 18 ºC / 54 and 64 ºF which will the mealworms fresh for up to two weeks. Excessive temperatures will increase metabolism and cause avoidable pupa formation.

Giant mealworms can be kept for up to two weeks in a larger container with a 20-50 cm / 1-2 " layer of moist peat moss or sphagnum peat (see the Suitable Substrates For Herptiles on RepVet.co.za for more info). The substrate should be kept moist, i.e. by spraying it with a spray bottle at regular intervals. When planning on keeping them for more than two weeks rather use a food substrate mentioned above. Containers with mealworms should be stored between 15 and 18 ºC / 59 and 64 ºF which will keep them fresh for several weeks.

To maintain feeder mealworms in a state of dormancy (sleep), a container with bedding and worms, covered with a piece of cloth to prevent condensation, can be stored at temperatures between 4 and 10 ºC / 40 and 50 ºF. Most refrigerators are set at about 5 ºC / 41 ºF.

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Breeding Feeder Mealworms:

Feeder mealworms breed prolifically and is relative easy to culture. Initial stock can be bought directly from breeders or specialist pet shops. Larvae are usually sold in small containers or large tubs.

Some breeders prefer to keep all stages in the same container while others prefer to separate them. When breeding with all the life stages in the same container make sure all the keeping requirements are met and wait until new worms arrive.
When stages are separated, the beetles are kept in one container and is moved to another clean container after the arrival of larvae. It usually takes about three months for for eggs to hatch and for new larvae to become visible (Table 2). Larvae and beetles will nibble and injure or eat pupae, which can kill them or make them unviable. Pupae should be removed to their own container until they metamorphose to beetles. Beetles can be moved to the rest of the breeding beetles.

100 to 250 mealworm larvae can be placed in an appropriate sized container. Depending on the age of the initial stock, it can take several months before pupation takes place. Beetles will emerge and start to mate approximately two weeks after pupation. From here on matings will take place all the time. Male beetles are usually significantly smaller than females. Beetles buried in the bedding are usually laying eggs. One female can lay about 500 eggs in her lifetime. Eggs are about 1 mm / 1/20th". Beetles will mate and lay eggs for approximately 4 months, after which they die. Eggs hatch after one to four weeks where tiny larvae emerge. The whole process can take a few months (Table 2). During the whole mating period containers should be undisturbed.

Table 2 - Average time required for the completion of each life stage of the Common mealworm under average conditions:

Stage	Time (weeks)
Egg	1-4
Larva	10
Pupa	1-3
Adult (beetle)	4-16

To breed giant mealworms the larvae should be stimulated to pupate and complete the cycle. Without stimulation the larvae can grow for long periods and die without ever pupating. It is said that pupation take place after separating larvae into small ventilated tubs or film containers with a layer of bran. Beetles should be added to a container with a layer of wet sand, where they will lay their eggs. Sand are available from specialized pet shops, some large toy shops, building material suppliers or some hardware shops. Keep the sand moist by regular spraying and/or by covering it with moist newspaper. Small larvae emerging from the sand will soon be visible and should be transferred to a container with proper bedding.

Over time a build-up of a powdery residue will appear on the bottom of keeping and breeding containers. This so called frass consists out of waste and eggs. It can be sifted out once in a while by using a fine sift and can be added to a new container with bedding. Eggs will take about one month to hatch. A few weeks after hatching the mixture can be sifted again, after which the tiny larvae can be added to the initial group or to start a new colony.

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Feeding Mealworms To Other Animals:

Mealworms can be fed to an assortment of animals. Larvae, pupae and the beetles can be fed, but they should never be fed as main part of any diet because of their high fat content (Table 1).

Larvae have relatively hard cuticles, (a layer consisting mainly out of indigestible proteins and chitin). Newly secreted cuticle is flexible, elastic and soft and probably more digestible than when it is dried out and hard i.e. it is better to feed newly hatched larvae. The cuticle causes larvae to stay alive in the gut of the animal for long periods. This is especially true for animals which do no chew before swallowing, such as amphibians and some lizards. Some literature suggests that larvae have the ability to literally chewed their way right through the guts of reptiles. Larvae can also bite and hold onto gut lining, where the head and mouthparts can remain behind after the body of the insect is digested. This can cause abdominal pain, obstructions and infection. It is therefore advisable to remove the heads of larvae, i.e. by using tweezers, especially giant mealworms, before feeding.

Mealworms have a negative calcium to phosphorus ratio (Ca : P). To increase the nutritional value of mealworms they should always be dusted with vitamin/mineral combinations prior to feeding. See the dusting & gut loading sections for more info in the topic.

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Feeder Mealworms & Other Feeder Insect Related Books:

We strongly recommend reading the following books on keeping and breeding feeder mealworms:

Click on each book for more information

Keeping & Breeding Crickets As Feeder Insects

"If you think I should add more information to this section or think that something is incorrect, contact me and let me know. I would love to hear your ideas or methods you might use that is different than ours."

Last updated 9 April 2006 by Renier Delport

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