I think they probably are the skins of the mealworms tiki. I keep mealworms and they do moult, and it does look similar to fine tan woodshavings. worm castings are dark brown and the manure from the worms, not all that light in weight, almost a compost consistency but denser and finer. Im sure there would be something in those mealworm "castings" that would be useful to the plants but they wouldnt have the same benefits as worm castings. hope that helps

I bet that that material would make good feed for wormbeds if you have any. wouldn't be hard to find out with a cup or two in a bed.

Tiki - I think we live in the same area (around Los Angeles) so it's the same supplier most likely. How did they do in your community garden? I think the "castings" are a combo of real castings and moulting ecoskeletons but I still think they are good for our clay soil, although not the same beneficial microbes as earthworm castings have.

Some lady is advertising meal worm castings on Craigslist for $15 for a 35 pound bag. I had read this thread before I went to her house so asked her if she had gotten her castings from the place in Compton that I think you were hinting about, and that I read you can get it for free. She said yes her castings were from that major mealworm producer but they weren't free. I offered her $13 for the bag and she said OK. When I got home I weighed the bag and it was only 28 pounds, not 35, and the bag said hybrid wheat on it, but I figured they were just recycling the bags so didn't care about that. My question, is the supplier Rainbow farms in Compton or Long Beach, and are the castings really free if one goes direct to them, or if you have to pay how much is a bag and what size is it? The castings were very light and looked sort of like termite or furniture beetle sawdust if you ever saw that. Does one have to worry about beetle eggs in the mealworm castings hatching and flooding your house and yard with beetles?
http://www.greenpeople.org/listing/Rainbow-Farms-Fertilizer-40597.cfm

I have had experience with mealworms and with Rainbow when Ihad a pet store years ago. You will find that they are a very reputable company with a stringent quality control. Worms are fed a high quality food.

If your intention is to drop some good quality compost into your garden then the mealworm castings work well especially if free or cheap. You do not have to worry about beetles hatching from eggs simply because you are not going to find eggs from the mealworms themselves. The beetles lay the eggs that hatch into mealworms, then they pupate and then break out as beetles to repeat the cycle.

It is much easier for an individual to raise significant numbers of red worms in a home composting system than mealworms, which is why you will not see mealworm husbandry addressed here.

Now I see another person in Long Beach advertising on Craigslist for meal worm castings for $2 for a large bag, so I must have overpaid for what I just bought. I am guessing a lot of people are getting these castings for free or very low cost and reselling it. Maybe I might even try that myself if I can get to the real source in southern California.

I just went out and was ready to use the mealworm castings I just bought and the bag was crawling with live beetles. Glad I didn't mix it with any potting soil. Is it even safe to use out in the garden, or will I bring a beetle infestation upon myself if I do?

Are these beetles the size of the last joint of your pinkie finger? If they are they might be giant mealworm beetles. if so put them into a container with damp peat moss in the bottom and feed them some dog or cat food and they will lay eggs in the peat. Later you will have a colony of meal worms you can use.

Or the bag may have been contaminated by some other kind of bug.

Mealworms are not usually a problem if they get away. (nor the beetles). And you live in the state that has the most stringent control on insects in the whole country. I would not be concerned.

I just called Rainbow Farms and the lady I talked to said the mealworm castings are sometimes free, sometimes a dollar for a ten pound bag, depending upon how much they have and how much they want to get rid of. She said the castings are mostly the skin of mealworms that molted, and the castings do normally have some live darkling beetles and live mealworms in them. She didn't know if the adult beetles or the larva would be harmful to a garden, does anyone here know? Wikopedia says the beetles will eat live and decayed vegetation, and for sure the mealworms would because one of the things they feed them is carrots.

It must be like waking up on another planet. To go where no man has gone before. I wish you had some fish or chickens to feed the bonanza to. I wonder what they have been eating in the bag. Maybe digging a hole in the ground to put the bag into would be good. I'd get more if free. Good stuff for the garden. Just needs to be something or othered first.

One more comment about the mealworm castings I bought. When dry they hardly smell at all. But mix them with some potting soil and wet it and they develop a terrible stench. They are definitely not suitable for plants to be kept indoors due to the smell. Outside I would recommend covering them up with a layer of dirt to keep the smell down.

Well I finally found this Rainbow Mealworms company, and yes it is very hard to find. Even printing out a google map it is hard to find, because the map doesn't show a railroad tracks running right down the middle of Meadowbrook Street which you have to go on to get to Spruce Street, and if you are on the wrong side of the tracks you never see it. And Spruce Street itself is a narrow street that looks more like an alley.
But anyway I called up this morning and the lady I talked to said the mealworm castings were a dollar for a 16 pound bag. When I got to their bait store the guy said they were $3 a bag. So I cried and moaned about driving 25 miles to get there because I was told they were a dollar a bag and finally got him the compromise at $2 a bag and bought 5 bags. When I got home I weighed one of the bags and it weighed 32.5 pounds, so I guess by bargaining I did get it for a dollar for 16 pounds.
BTW, I see someone in Orange County must be buying these bags of mealworm castings and reselling them for $15 a bag on Craigslist.