Harpegnathos just let the rests of the shells in the nest or just use them as material to build their nestchamber just like the shells of the pupae they use for "wall-papering".
In nature at least Harpegnathos saltator had been described as ants that only have one primary nestchamber and one unter the primary one. The lower one was once described to be a disposal of trash like the leftovers of food and stuff and apparently some insectlarvae and other stuff lives in there.
However that was a short describtion that was made by a scientist while collecting colonies for experiments with the ants, when I remember correctly it was the one where they first counted the amout of gamergates in Harpegnathos saltator colonies.
However I don´t fully belive the describtion by now. I hadn´t had the chance to make experiments by my own by now but what I know from the nest building of Harpegnathos saltator is that they surley have only one nest chamber where they store their paralyzed prey and brood in, but the workers seem to have a chamber of their own... well thats just a vague guess of course, also I have never seen a sinle specimen of Harpegnathos saltator in wil.
However that data isn´t necessarily right for Harpegnathos venator as well. They look much alike but there are some mayor differences between those two species despite the color and the stronger body of Harpegnathos venator.
Another thing you have to have in mind when talking about mites is that the mites, that digest dead crickets in nests of ants in keeping, aren´t necessarily bound to suck the haemolymph of living creatures.
In the case of Harpegnathos venator it seems that the mites that feed on dead crickets also are able to sit on the Harpegnathos workers and use them as a ride to their food. There also is a theory some ant keepers like to mention; the mites feed on the paralyzed prey in the nest.
There is some things I don´t like about that theory. First of all Harpegnathos venator and Harpegnathos saltator tend to clean their prey very often. So the prey that lies around in the nest is quite clean. Another thing that I´m not quite sure about is weather the venom Harpegnathos spp. use is still potent after the insect is in the nest, I mean if the venom can still affect other insects despite of Harpegnathos spp.. I guess that the venom consists of some peptides just as many neurotoxines do and can be diguested by most living things and wouldn´t be dangerous for anything when eating the paralyzed insects. But that would pretty sure kill the insect so I guess the venom might be something else since I always read that the venom only paralyzes the prey.
The amount of food leftovers that stays within the nest is small within nests of Harpegnathos venaotr compared to the nests of Harpegnathos saltator, which even used it to cover larvae that just were turning into pupae and also tended to close their nest whit corpses of insects.
To end this utterly long post here; I do not understand why Harpegnathos venator always get mites and I don´t really think there is a easy way to explain it and we surley won´t understand why whithout ever digging up one of their nests in nature.
[I will move all the posts to your original discussion thread once I find some time since I will AGAIN have to change all the links and stuff.]
Regards
Kaj