Back to Home Page  


How to Grow Mealworms (includes step-by-step photos)   

What you will need to get started:

Clear storage bins.  Lids of storage bins need to have centers removed for proper air circulation.  You will need to hot-glue screening material over the hole to keep out moths and mice.   This year I had to add another heavier wire-style mesh over the fine screening to keep out a persistent RAT.


Add a few inches of substrate such as wheat bran, corn meal, chicken feed or oatmeal.  Wheat bran is available cheaply from farm suppliers and that is what I use.  Then place a flat "food" lid (from cottage cheese container, etc.) on top of the bran and put several carrot slices or other "wet" food of choice on the "food" lid to keep the substrate dry.  Damp substrate and wet conditions cause mold and mite infestations.  Cover that with a lightly misted paper towel to provide humidity (important for those of us living in dry semi-desert areas).  Mealworms will crawl up onto the lid to get moisture from the "wet" food.

Other Food Choices:  Cactus slices (for those in semi-desert conditions), aloes, potatoes, plums, cantaloupe, watermelon and other vegetables and fruits you might have on hand.  Keep it fresh.

For a few bins, you can purchase a starter colony of mealworms from the pet store.  If you have access to beetles or pupae from a source who raises mealworms, that will give you a head start.  Those wanting to generate 10,000 or more mealworms per week will want to order about 50,000 large mealworms or beetles  from suppliers such as Rainbow Mealworms in Compton, California.   Shown below are mealworms at maximum size just prior to pupating.

Check on your starter colony every couple of days to make sure wet food is available and/or still fresh and to slightly mist the paper toweling. 

When your starter colony begins to pupate (similar to a caterpillar chrysalis),  pick out the dormant pupae from the mealworm bins. 

Picking out pupae individually from mature mealworm bins is the time-consuming part of raising mealworms in large quantities.  Many thanks to Olivia Olessi for her help with this task during the busy season.

  Tip to make sorting bins easier


The pupae are pure white at first (see photo below) and then they turn beige as they mature.  

Collect pupae into their own bin, cover pupae with paper toweling, spritz lightly every day or every other day for humidity and wait for the beetles to emerge.   Pupae are dormant and need no food but I put them on a layer of substrate (bran).

At least every other day, check the pupae bin to see if beetles have emerged from the dormant pupae.  New beetles will be hungry and thirsty and need to be put into a prepared "beetle breeding bin".   It is fairly easy to remove beetles quickly from the pupae bin because they tend to cling to the slightly damp paper toweling (see below).  Simply lift the paper toweling from the "pupae" bin and shake the beetles into the "beetle breeding" bin.  New beetles are white, then they turn golden brown and then a black.

The "beetle breeding" bin should have a few inches of substrate such as wheat bran and I add a sprinkling of Wheat Germ and Brewer's Yeast.   Other nutritional options are powdered calcium, powdered milk, kitty kibbles and other extra nutrients.  For moisture, put sliced cabbage (or other food choices) on a flat lid placed on top of the bran.  Put a damp paper towel over the food lid area, spritz every other day and check to make sure moist food is still available on the lid.  Beetles will eat some of the moist food and lay their eggs.  They also like to crawl up and under old cardboard egg cartons.

Each week, prepare a new "beetle breeding" bin so that beetles in each "beetle" bin will breed at the same time, lay eggs at the same time, and eventually die off at the same time.  After a few weeks (depending on temperature), the beetles of that bin will have completed their life cycle and you will begin to see tiny hatched mealworm larvae on and near the "food" lid. 

When that happens, put any remaining live beetles into one of your other beetle bins and put carrot slices (or other moisture food) on the lid for the young mealworms.  I'm told beetles prefer cabbage and that mealworms prefer carrots.  However, their preferred moisture/food choice (for those of us in semi-desert areas that can grow them) are aloes and cactus with their "jelly-like" moist centers.   I slightly sink an edge of the "food" lid into the substrate to make sure tiny larvae can find the food moisture.  Skins of cactus form their own "lid".   Paper toweling is misted in mealworm bins same as is done with beetles.  You now have a "clean" bin of tiny nursery mealworms.  The only upkeep from that point is misting the paper toweling and replenishing the moist food.

As mealworms mature, their increased sized and activity will cause the "food" lid to sink into the bran substrate mixture.  Just pull the lid back up on top of the bran each time moist food is replenished.   When the bin is full of small-to-medium sized mealworms, there seems to be a greater need for moisture.  If you have cactus/aloe pieces, great.  If not, try plums or other food choices which have more moisture than carrots.  If too many worms are crowded into a bin, they generate too much heat and humidity.  Adding more bran will suffice if there is only slight overcrowding.  Otherwise, divide the crowded mealworms into two separate bins (or start using some).  During warm weather (greater than 80F), it is especially important to not have overcrowded or damp bins.

In order to regenerate the beetles to keep your colony producing, you will need to set aside some of the mealworms so they can grow to maximum size, pupate, and turn into beetles that will lay more eggs.  In the setup shown,  bins of saved (maturing) mealworms are in the upper two shelves to the right (over the file cabinets).  When they eventually pupate, they are picked out and placed into the two lower "pupae" bins.

When beetles emerge in the pupae bins, they are then shaken from the paper towels into a new "beetle" bin which is then placed on the upper left top shelf.  As new (first-week) beetle bins are added, the older beetle bins are moved downward to the (2nd-week) lower shelf, then the third (3rd-week) shelf.  The shelf below that is the "baby worm" shelf, and then they move to the "small worm" shelf and then finally to the last "mealworm" shelf.  

They are then ready for use or will be saved to mature into pupae by relocating the bin to the section above the file cabinets.  By this time, almost all of the bran (or other substrate) will have been eaten and the residue (frass) will be of a fine sand-like texture that can be easily sifted from the mealworms.  If you are planning to let the mealworms pupate, sift out and throw away the substrate residue and put the maturing mealworms into a  fresh bin of substrate/carrots and wait for them to pupate.

This system of 27 bins can generate about 10,000 to 15,000 mealworms per week.  Even with this large system, there are never enough mealworms during the nesting season.  The bins dwindle down to about half the amount by the end of each nesting season. They are built back up (mealworms used only for propagation) during the fall and winter months so that each nesting season begins again with full racks of bins.

Bluebird Trails:  I use mealworms as a monitoring tool for a  100-box bluebird trail.  See link to Home page (below).  During each box check, mealworms are placed at the base of tree trunks or other firm surface (not in the sun where they will burn easily and not in close proximity to the nestbox). 


Also See:   How to Feed Wild Bluebirds

If you came to this site looking for answers to Bluebird-related questions, be sure to visit my Home page or you may contact me,


 Mealworms attract ants and other competing birds which you don't want them near your nestbox.  Birds are easily trained to find "hidden" mealworms after the first couple of offerings and your biggest chore will be to not let the other area birds catch on to the mealworm routine or they will outcompete the bluebirds. 

Offering mealworms during nestbox checks lets me know within seconds if both bluebird parents are in the area.  Bluebirds parents will quickly approach and find the mealworms.  If chicks are too old for the box to be opened, you can tell from the sound and intensity of their chirrups if all is OK.   Plus, mealworm offerings during weekly checkups gives bluebird parents a semi-vacation from the constant search for food.


You may contact me, Linda Violett
As of June 15, 2012