Can bedding be heat sterilized a second time?

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Can bedding be heat sterilized a second time?

I recently had a die-off in a couple of trays of mealworms. About 10% of the mealworms died over two days, turning black from the head end.
Temp about 69 degrees F and humidity about 55-60% overall in the room. Your bran bedding, 1.5" deep and cleaned of frass twice per week. Density of about 1200 1-inch worms in a tray with 142 square inches of surface area. Cut carrots used for moist food, uneaten carrots removed and replaced with fresh ones every 2 days.

The bedding does not feel damp and I see no signs of visible mold, there is no smell except for the scents of bran and carrots. 6 other trays of mealworms from the same batch are fine - the only difference I could see was that the mist from their humidifier might have been landing more directly onto those two trays. Of course I have relocated the humidifier in case that caused the trouble.

Any idea whether the worms were killed by the cold or by unseen mold?

I removed all dead worms, put the live ones in the refrigerator to be fed off to the birds, and cleaned the bedding of all dead worms, food and frass.

If you think it's mold, can I re-sterilize the bran in the oven at 175 for 20 minutes to kill any mold spores without hardening the bran? Or do I just need to compost the bran as a lost cause?

Status: Open Oct 25, 2025 - 10:00 AM

Bran / Bedding

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admin

Oct 24, 2025 - 06:38 AM

Your conditions sound perfect, and if your bran had mold, you would notice a change in its odor, color, or texture.

I would not try to re-sterilize your bran. If it does have mold spores, it's best to do away with it and start over again.

Was this a new batch of mealworms? Can I ask, did the dying ones turn black on the ends first? Or did they curl into a C shape and turn black all at once? Did you notice any behavior like them congregating at the corners of your tray?

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on 10/24/2025 12:17:14 PM | Like (0)

I assume that if my worms were killed by mold there would indeed be spores in the bran. However, there is no dampness, no visible signs of mold, no change in color or texture, and no odors. It looks, feels and smells just like all the other bedding in the farm. So I'm assuming that mold was not the cause, and I'm looking for another explanation.

I bought 5000 large mealworms from Rainbow a few weeks ago and distributed them into 4 trays as described above. The four tiers were stacked together in a column, with batches others below them. The large worms were okay for awhile so I assume they arrived healthy. The only major change over that time was in the weather here, so that the temperature in their area dropped from about 73 degrees to 69 over a few days. This would have been a shock to them as your conditions are probably much warmer.

Then I began to see the die-off, but in only the upper two of the four trays from that batch. All other trays in the colony, including lower trays in that column, appear to be fine. The only thing I could see that was unique about those two trays in the whole column is that they were almost directly in the path of the mist from the humidifier, which I then moved.

The dying worms did not curl up. They remained straight but limp, turning black only at the head end to start. As to the behavior, yes. All my mealworms and sometimes even the beetles are congregating in the corners and outer edges of their trays. They are not escaping heat because the temperature in the center of the bedding is cool - about 70 degrees. And there's no frass in the beetle tray as they have screening in the bottom.

I'm wondering if my worms died of hypothermia, as cold air+moisture robs body heat. Is it possible the healthy worms are congregating in groups to conserve warmth rather than to escape it?

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admin

Oct 24, 2025 - 12:46 PM

I found your order that was two days in transit and picked up at the Post Office 22 days ago (thank you for using your PO Box!). That's a long time for them to be healthy on arrival and suddenly die off all around the same time so I don't think it can be the conditions at USPS.

As for the congregating, we ask that because worms will try to stay warm by congregating at the corners of your bin. They will even try to pile up so some can escape over the edges! (they are pretty smart for invertebrate creatures).

I can only guess that the humidifier caused your bedding to get damp and raised the humidity too much in those bins, allowing fungus and bacteria to grow. If that sounds like the case, you'll want to replace all the bedding and disinfect the tray.

Your mealworms breathe through spiracles in their shells into little tubes called tracheae; when bedding is too damp, the dust and water from the bran can clog these little holes and tubules. The dead will usually appear plump (not skinny like when dehydrated) but will turn black in the area where the tracheae are clogged.

Does that sound like what might have happened?

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I assume that if my worms were killed by mold there would indeed be spores in the bran. However, there is no dampness, no visible signs of mold, no change in color or texture, and no odors. It looks, feels and smells just like all the other bedding in the farm. So I'm assuming that mold was not the cause, and I'm looking for another explanation.

I bought 5000 large mealworms from Rainbow a few weeks ago and distributed them into 4 trays as described above. The four tiers were stacked together in a column, with batches others below them. The large worms were okay for awhile so I assume they arrived healthy. The only major change over that time was in the weather here, so that the temperature in their area dropped from about 73 degrees to 69 over a few days. This would have been a shock to them as your conditions are probably much warmer.

Then I began to see the die-off, but in only the upper two of the four trays from that batch. All other trays in the colony, including lower trays in that column, appear to be fine. The only thing I could see that was unique about those two trays in the whole column is that they were almost directly in the path of the mist from the humidifier, which I then moved.

The dying worms did not curl up. They remained straight but limp, turning black only at the head end to start. As to the behavior, yes. All my mealworms and sometimes even the beetles are congregating in the corners and outer edges of their trays. They are not escaping heat because the temperature in the center of the bedding is cool - about 70 degrees. And there's no frass in the beetle tray as they have screening in the bottom.

I'm wondering if my worms died of hypothermia, as cold air+moisture robs body heat. Is it possible the healthy worms are congregating in groups to conserve warmth rather than to escape it?
he dead worms were indeed plump, so that is probably what happened. I guess I'll need to find a way to warm up their area.

Can bedding be heat sterilized a second time?

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