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How to Raise Mealworms

How to Raise Mealworms

Mealworms may be easily raised at home by following a few suggestions.

An initial supply may be obtained from us or found in feed, grain, or meal in a barn or feed room. A wooden box or box eight to ten inches deep, twenty four inches long and eighteen inches wide makes a satisfactory rearing container. This box should be half-filled with MEALWORM BEDDING / FEED. A few scraps of cloth or wrinkled paper will assist in preventing the meal from packing too solidly.

Proper ventilation and a fairly even temperature are essential to prevent mold growth. Cheese cloth tied over the tray will provide ventilation while preventing the escape of the adult beetles. A two inch strip of sheet metal should be securely nailed to the inside walls of the tray above the food mixture to prevent the insects from crawling over the side. Some moisture is necessary. This may be best provided by the addition of some moist foods such as pieces of raw potatoes, carrots, ripe apples or banana peels. We sell a product called THIRSTY CRICKET which is a jell made specifically for watering live insects.

After the tray has been prepared and mealworms added, the tray should remain undisturbed for several weeks to allow the worms to develop. The larger worms will then have changed into the pale, quiet stage which later changes into the adult. The colony should then be prepared for expansion. A little mealworm bedding/feed may be sprinkled on the surface of the mixture and a few pieces of apple and carrot added followed by a second sprinkling of mealworm bedding. A close watch should be kept for several weeks until a number of adult beetles appear.

Another tray should then be provided, prepared with the same food mixture as in the first. The adults should be placed in this tray to lay eggs for more young worms. As soon as these young worms have grown sufficiently to be handled they should be put in the first tray and allowed to grow as large as desired. By using a two tray system, one should be able to provide a continuous supply of worms.

The food mixtures must be discarded, the trays cleaned and scoured, and a freshly prepared food mixture put in occasionally for the successful rearing of the worms. Old food mixtures will become foul unless occasionally changed.

Quick Tips for maximum productivity:

Place large mealworms in a shallow plastic sweater container. Cut a hole in the top for ventilation and use a hot glue gun to adhere window screen to it to keep critters out. Add 2-3" of Mealworm Keeper:

For moisture, add Thirsty Cricket Gel to a low (1/2 " container). Replace at least weekly or if moldy.

Ideally keep at around 80°F (room temperature is fine too) and around 70% relative humidity. Use a moistened sponge in a baggie/container (open side up above grain) for additional moisture. Periodically (e.g., every 1 to 2 weeks) sift out beetles from bedding with eggs/tiny worms. Once worms are big enough, sift frass (waste) and bedding out once a month, dispose of in garden, wash and dry container, return worms and add new food.

Timetable and Lifecycle: Tenebrio molitor have an egg, larva, pupa and beetle stage. Depending on food and temperature, it takes about hundred to several hundred days for them to complete their lifecycle. Therefore, if you want worms in the spring, start your colony in November or December. For each 20 beetles, you should get about 350 adult mealworms in 200 days. Here is the lifecycle if the colony is kept at room temperature (~72 F.) I found it took much longer for the pupa to convert to the beetle stage.

Stage Time* Egg 4-19 days (usually 4-7). Another source says 20-40 days Larva 10 weeks. Visible after about a week Pupa 6-18 (18-24?) days Beetle 8-12 weeks

* time depends on temperature, relative humidity, food, etc. Different sources report different time frames.

Eggs hatch into larva.

Larvae burrow below the surface of the grain and undergo a series of molts (10-20, average of 15), shedding their exoskeleton (looks like Cornflakes). The last molt occurs about three months after the egg stage. Newly molted worms are white, and the exoskeleton has not hardened so they may be more digestible. The fully grown larvae (worms) are golden brown and 0.98-1.38 inches long, with about 200 to an ounce.

The larvae come to the surface. They turn soft and plump, stop moving, curl into a "C" shape, and then transform into naked white pupae that turn yellowish brown after a day. They look sort of like alien grubs. The pupae don't eat or move much. If you purchased your worm stock fairly large, this transition may happen in a few weeks.

After 6 - 18 days (7-24 days or more), the pupae metamorphose into beetles. At first the beetle is white/light beige with a soft shell, and then it darkens and hardens to red, brown, and finally turns dark brown/black after about 2-7 days. The beetle is about a half to three quarters of an inch long and slightly flat. Males and females are indistinguishable. They can not fly, but they can move very quickly. I've noticed some do not develop property (e.g., wing covers) and look ragged. You might want to use these as bird food.

Beetles lay their eggs 9 - 20 days after emergence. They lay for two or three months, and then die. Each female beetle lays about 275 tiny, bean-shaped white eggs - about 40 per day. The eggs are seldom seen because they are sticky and rapidly become coated in substrate. They are about the size of a period at the end of this sentence - you would need to line up 20 to equal an inch. [Note: Birds may eat live beetles if offered.]

Egg incubation takes 4-19 days (average of 12.)

The cycle begins again as the eggs hatch into tiny whitish larvae, which may not be easy to see for several weeks.

In 4-6 weeks they will be about 0.5" long.

Stock: Get at least 100-1,000 large mealworms from a mail order supplier or pet store; or from feed, grain, or meal in a barn/granary.

Do not buy "giant" mealworms, as they may have been treated with an insect growth hormone to discourage them from morphing into beetles, so they will grow larger. If giant mealworms do morph into beetles, they will be sterile.

To jumpstart your farm, ask you local pet store if they have any adult beetles you can get.

Container: As long as the larvae are 1" or more below the top of the container, they can't get out. Mealworms may thrive more in a container with a large surface area. Some people keep the container(s) in a laundry room, garage or basement.

A clear container will let you see how much frass (waste) has accumulated. Use a shallow (e.g., 2-5 gallon capacity, 6-10" deep x 24" long, or 10" x 17" x 6") plastic container. A shoe box size or sweater storage container (Rubbermaid, Sterilite, etc.) will suffice. A pail can also be used. If you are going to separate the stages, a four drawer container like the kind found at Wal-Mart or Target can be used. A 64 quart Rubbermaid container holds 50,000 to 100,000 larva.

Some people use wooden containers, but if the sides are too rough, the worms may be able to climb the walls.

A larger surface area may improve survival by dissipating heat. Too many worms stored in too small a container will overheat and die (e.g., 5,000 worms in a 2 gallon pail=dead worms.) The mealworms should probably be only 3-4" deep.

Ventilation and Cover: Ventilation prevents mold growth. Darkling beetles do have wings, but can't fly. Some commercial farmers do not cover their bins. Since mice, rats, cockroaches and some spiders will eat mealworms, the container should be kept closed. (One bluebirder in Texas found a scorpion in with her mealworms!) A tight fitting cover will also keep flour and grain moths out. Options:

If the container comes with a plastic cover, drill holes in it. If condensation forms on the inside of the lid, you need more holes. Cut a section out of the middle of the lid and use a hot glue gun to glue some fine window screening material to the inside of the lid, around the hole. Make a cover for the container out of window screening. Temperature: The ideal temperature to maximize growth is 77-81ºF, but ~ 72-74ºF is also good. Mealworms do reproduce in temperatures ranging from 65-100 F, but temperatures above 86ºF negatively impact growth and development (inhibiting pupation). The duration of the pupal stage will depend on temperature. It is six days at 91.4ºF, seven days at 80.6ºF, ten days at 75.2ºF and thirteen days at 69.8ºF.

Temperatures below 62ºF may halt reproduction. In cold temperatures the larval stage can last two years. Chilling worms and then re-warming them may significantly delay pupation. Prolonged exposure to temperatures below 40ºF may kill the worms.

I am using a 500 watt rheostat controlled ceramic reptile heater suspended over the container to keep temperatures high enough in my drafty home. The heater is in a metal hood, and sits on top of the Rubbermaid container, on a circular metal window screen hole. Because it dries everything out, I put the cabbage/potato wedges underneath fabric, and have several plastic containers filled with water sitting on top of the bedding.

Light: Consistent with the name darkling beetle, they prefer the dark. Keep the container out of direct sunlight. However, one source indicated that if mealworms develop faster when provided with light. To obtain a supply of adult beetles in the fall, the usual hibernation period of the dark mealworm (a different species) can be prevented by exposing the fully grown larvae to continuous light.

Moisture and Relative Humidity: Mealworms do require moisture. Too little moisture slows growth and reduces size. Too much can produce mold. If larvae are provided with dry food, they can survive and produce one generation a year. If they are provided moisture, they will undergo six generations per year and will be fatter.

Beetles lay more eggs when the relative humidity is higher - ideally 70% (55-80% is good). In one experiment, at a relative humidity (R.H.) of 20%, beetles laid an average of 4 eggs each, but at 65 percent R.H., they laid an average of 102 eggs each.

Adult worms also become more active between 90 - 100% R.H. Keeping the culture moist also prevents cannibalism.

Add a chunk of cabbage, raw potato (half a potato, or a chunk about 1"x3"), a slice of bread (which the mealworms will also eat), romaine lettuce, kale (high in calcium and inexpensive), yam (also nutritious) or apple slices (1/4 of an apple is enough for 1,000 mealworms, once or twice a week - I find apples get moldy too quickly). Some people use celery (e.g., bottom end of bunch), broccoli stems, carrots (grated carrots on a plastic lid), banana peels, or asparagus chunks. Cabbage leaves do not get as moldy as some other choices. A crust of bread (replaced when dry) can also be laid face down on the bedding. You may wish to wash/peel vegetables first to prevent the introduction of pesticides. Place potato/apple slices cut side up, even with top of bedding. By putting the skin side down, you keep the bedding/dry food from getting too moist. Try kiwi skin with about 15% of fruit still in it (after scooping out the rest with a spoon for your own enjoyment). A.M. Prendergast found that it made mealworms grow about 3 times fatter and 30% longer in just 2-3 weeks versus wheat bran alone. The worms also use the skin as a "cave" as it dried and curls up. Cover cabbage etc., with a cloth to keep it from drying out if you use a heat lamp. To make them easier to replace (every 2-3 days or weekly), put vegetable on a little plastic lid, tinfoil pie plate or a piece of cardboard, or stick a toothpick in it. Replace immediately if mold appears. More is not better. If you put too much in, or leave it too long, it will get moldy or become a gooey mess. If you use burlap or newspaper, you can spritz it lightly with water on a daily basis. Do not soak, and do not wet bedding. You can also put in a moist (not wringing wet) paper towel, changing it daily. You can put down a piece of aluminum foil under the dampened burlap/paper to prevent grain from getting wet. "Cricket quencher," a gel polymer that insects suck water out of, can also be used. It will not wet bedding material. Small amounts of moist cat food (like Tender Vittles) can also be used, and will provide extra protein. Placing adult beetles on moist blotting paper overnight may increase egg production. Place a small but tall (so they don't draw on) bowl filled with water in the middle of the farm to increase relative humidity. A sponge can be placed in the bowl to increase the moist surface area. Fawzi Emad uses a moist sponge wired to the container lid. You can also put the bottom of the sponge in a plastic baggie (to prevent the meal from getting wet and moldy) and stand it upright in the Mealworm Keeper. Re-wet the sponge weekly, and wash it when needed. Food/Substrate/Bedding: The more nutritious the food, the more nutritious the mealworms will be. Layer it in 2-3" inches deep. Replenish the food often, as the worms eat a lot. Change the food out about once a month. Feed the beetles too (same stuff). I mix up a big batch with supplements and store in it a plastic bin with a screw top lid so I don't have to worry about flour moths and other critters getting into it.

Fine particles (Mealworm Keeper) make it easier to sift out large mealworms.

A few scraps of cloth or wrinkled paper layered with the bedding will prevent the meal from packing too solidly.

Supplements: You can add the following to the dry food/bedding: wheat germ, finely ground egg shells or cuttlebone (for calcium), soybean meal, Wombaroo insectivore mix, fish flakes, fine mouse cubes, bone meal, graham (whole wheat) flour, and dry brewer's yeast (provides proteins and trace elements essential to the insects' growth and makes larvae grow more. Brewer's yeast can be obtained at health food stores. It's pricey, so you might want to buy it in bulk at a feed store or online. You can sprinkle the vegetables/fruit with calcium and vitamin supplements to add nutritional value. Experiments where skim milk (calcium source) was added to wheat bran (1:3 or 1:2 ratio) yielded better growth than wheat bran alone.

Cloth or newspaper covering: You can partially cover the food surface (about 2/3) with several layers of newspaper, brown grocery store bags, paper towels, or a folded piece of cloth. Leave space between the paper and edges of the container.

Worms will crawl between the newspaper layers to pupate, which makes it easy to collect them.

The beetles will lay eggs on cloth. However, it is difficult to get the beetles off the cloth when maintaining the farm. Beetles will also lay eggs directly on the food source. Or you could put thick, clean, dry hunk of bark on top of the bedding. The beetles will lay eggs on it.

Separating out worms: To remove worms to offer to birds or to separate them from eggs and beetles you can:

use a stainless steel sifter put a sheet or newspaper or grocery store bag or a plastic lid on top of the colony. The worms will crawl under it in a few hours. Repeat until you have taken all worms out and then replace the bedding. hold back on moisture for a couple of days. Then put a lettuce leaf, moistened piece of bread, or damp Bounty paper towel or blue paper shop towel (rung out - re-wet and ring out as needed) in the container on top of the bedding. The larva will cover the bread or lettuce. Shake them into a container until you get what you need. Cleaning: Remove dead mealworms or beetles. Dead larvae turn black. Dead pupae turn brown and shrivel up. Deformed beetles die early. Other dead beetles stop moving and their antenna crinkle up.

Frass: As the mealworms consume the bran, a fine, dusty or sandy residue will settle out on the bottom. Eventually, shed exoskeletons and waste products (frass) will build up, and a slight ammonia odor may be detected. That means it's time to sift the grain to separate the worms and adult beetles (don't throw out tiny larvae or eggs); wash the container, add new grain, and return the worms to the container. You'll probably need to do this at least 3 times a year. If the frass builds up too much, mealworms may turn gray and get black stripes and then die.

The frass (waste) can be used as fertilizer for flowers or vegetables. You might want to save the frass in a separate container for a bit and put some lettuce/cabbage to see if there are any mealworms you can separate out.

Sifters: You can make a sifter with #8 (1/8") hardware cloth or nylon reinforced screen tacked onto a wooden frame. If a sifter is made to fit in the bottom of the mealworm container, the frass will fall through the sifter, making it easier to clean the container. The fine hardware cloth may be difficult to locate (try a hardware store), but you can also buy a wire mesh basket from an office supply store, or use a contraption like a Double Over-the-Sink Colander with extendable arms (available at Linens N Things).

Colony "Cycling" or Maintenance: Some farmers leave worms, beetles and eggs all together in one container. If you do not separate them, do not change the bedding after the worms turn into beetles, as it contains eggs of future worms. Leave the bedding until you can see and sift out the small mealworms. You really should go through the entire farm about 3 times a year to separate out the beetles into their own container and add fresh bran. Too many adults in the container can eat eggs and reduce the colony's production.

Others farmers separate them out, since larvae and beetles might chow on the inert pupal stage, and beetles may eat pupa/eggs. If you start a new culture every 2-4 weeks, you will always have all life stages, they will be about the same age, and you won't run out of worms.

To separate the beetles out, you can catch the live ones easily by providing apple slices. They swarm to the apple - just lift it and shake off swarm after swarm. The handful that are left are easy to pick up/spoon out as they surface.


The best set up may be to have two containers that fit inside one another. Put the beetles in Container A, and put small holes (smaller than beetles, bigger than bran) or screen the bottom of that container. Sit Container A inside Container B. Every 2 days to 2 weeks, shake out the bran (with eggs) out of Container A into Container B. The beetles stay behind. Add more food and moisture sources as necessary to A as necessary. Once you've collected enough bran and eggs in the B, transfer the contents to a "nursery" container (Container C) with a source of moisture and let it sit for 30-40 days, and start over again. You can cover Container C bedding with a piece of newspaper or cloth that is spritzed lightly with water on a daily basis. I don't know how well this set up would work if you have a cloth with the beetles on it, as they may be laying eggs on the cloth.

Use three or more containers. Container A can be a big Rubbermaid bin with a lid. Containers B and C can be open shoe box size containers that sit inside of Container A. Or you can use the multi-drawer stacked containers, or simply three separate containers. Pull pupae out by hand of Container A (it only takes a few minutes if you do it every 2-3 days) Put pupae in Container B (no food needed.)

Let adults emerge before disturbing. Pick out the beetles out of Container B every couple of days (you can use a spoon) and put them in Container C with some bran and folded cloth they can lay eggs on. They are easy to see because unlike the pupae they have wiggling legs. After 2-8 weeks, take the beetles out of Container C and feed them to the birds/discard. Periodically remove any dead beetles.

Let the eggs in Container C hatch. For the first couple of weeks/months you can hardly see the larvae. Tens of thousands fit in a shoe box size container. Disturb the culture as little as possible during this phase.

When they are big enough to sift out from the grain, separate larvae out with a sieve or by hand and put them in Container A or more containers if you want to sort by age and size. One person has a simple set up in a collection of 12 used takeout containers, each about 5"x7"x3" deep. The beetles are in the first one. Every couple of weeks she sifts the egg-containing bran and beetles into two separate clean empty containers. Four or five months later this provides a batch of mealworms that are pretty much all the same size.

Storage: Worms that you don't want to reproduce can be kept in a closed container (with holes drilled in it) in the refrigerator. Lay a paper towel on top to prevent condensation. At 38ºF, or even 45-50ºF they will last along time (months) in a semi-dormant mode. One source says larvae can stay alive 80 days at 23ºF. They will not pupate in the refrigerator

Dusting: You can "dust" the outer part of mealworms with powdered mineral or vitamin formulations (e.g., Powdered Calcium [Ca2+] or calcium-vitamin combinations) prior to feeding it to an animal. Put larvae or beetles in a baggie, and gently shake them to coat them with the mineral-vitamin powder. Shake off excess before feeding to animals.

Uses: Mealworms are a good source of high quality protein. Some people do "gut loading" (offering extra food or protein to the mealworms) two days before feeding to animals. Larvae have a relatively hard exoskeleton made up of undigestible proteins and chitin. Recently molted mealworms may be softer and more digestible.

You might consider selling excess worms to a local pet store or a zoo. If you sell them, count out 100 mealworms by hand and weigh them on an accurate postal scale. Then figure out what the weight is for whatever quantity you are selling.

Bird food - caged and wild. Includes many songbirds and chickens, turkeys, guinea fowl, peafowl, quail, chukar, pheasant, and domestic ducks. Small birds like finches prefer 0.5" size (worms 4-6 weeks old). One source indicates that because of their high fat content they should not be fed as a main part of any diet.

Excellent fish bait. Mealworms last on the hook longer than many other kinds of live bait. They are one of the best baits for bluegill, perch, trout, whitefish and many pan fish, and for ice fishing.

Tropical fish. They especially enjoy newly molted larvae. Turtles (aquatic turtles of all sorts, box turtles, tortoises), reptiles (sailfin lizards, chameleons, fringe-toed lizards, basilisks, water dragons, basilisks, anoles), frogs (e.g., dart), toads, salamanders and newts. See dusting - it's a good idea to dust mealworms fed to desert or basking reptiles with a vitamin D3 precursor and a calcium supplement like Calsup®, especially when D3 light lamps are not used.

Small mammals, e.g. mice, hedgehogs, shrews, sugar gliders, moles, voles, marmosets, bats, rats and other insectivores.

Scorpions, praying mantis, centipedes, large insectivorous spiders, etc. Human consumption. Yes some people actually eat them. Freeze for 48 hours first. They will keep in the freezer for a few months if they are properly wrapped in airtight bags or containers. Rinse under running water before cooking. They can also be dried in the oven, and used in place of nuts, raisins and chocolate chips in many recipes. Nutritional Value: (Source:

Stage Dry Matter % Moisture % Crude Protein % Crude Fat % Ash % NFE % Larvae 43.05 56.95 48.31 40.46 2.92 8.31 Pupae 38.39 61.61 55.30 36.54 3.27 4.89 Adult 42.10 57.90 59.43 28.33 3.16 9.08

Problems with mites: Sometimes a mealworm colony gets infested by grain mites (Acarus sp.) The mites may come from the mealworm supplier, in bran, or litter from poultry production, and may infest a colony that has been around for a long period of time. Excessive moisture may be a contributor. They are prolific breeders (800 eggs/female) and can withstand temperatures of 0 degrees and still hatch when brought to room temperature.

The mites are tiny and round, whitish or tan in color, and have eight legs. They may cling to air holes and look like very fine sawdust. Mites can not fly.

To prevent mite infestation:

Use only Exotic Nutrition Mealworm Keeper. float mealworm containers in water (sort of like a moat); or put the container up on legs, each of which sits in a small container of water (which will also keep ants out). use vaseline (a 2" wide band on the outside of the container just after you wash and dry it) to prevent mites from getting into a worm bed. Blaine Johnson thought using aplies and potatoes as a moisture source may have connected to a mite problem he had, and switched to carrots.


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