Diploptera punctata nymphs dying

[satchellwk]

Well, my pacific beetle mimics finally had their first litter of nymphs, however, to my dismay, all but one died in the span of 3 days. I don't know what caused it, because all my adults have been fine. The enclosure is a gallon-sized pickle jar with a lot of holes punched in the lid, so it has some ventilation, but not much. I give them moist food (like apples, pear, etc.), and every few weeks they get a small spray, but, besides that, they stay relatively dry. There is a plastic plant in there, along with a hollow piece of wood to climb. There isn't much dry leaf or rotten wood matter in the substrate, but I don't think any of these would wipe them out so fast. Any ideas? I still have one, and he's active and eating well, but I didn't really see any signs from the others before they died; one day they were walking around, the next they were dead.

Any help is greatly appreciated. I may be able to post an enclosure pic later.