Dwarf white isopods, T. tomentosa, and they are less a pet than an infrastructure component.
Tiny, blind, parthenogenetic, and living entirely within the substrate. You will rarely see them. What they do is consume mould, waste and decaying matter in a bioactive enclosure, and they are the standard choice for that job in high-humidity setups where other isopods struggle.
Parthenogenesis means a single starter culture populates indefinitely without any pairing, which puts the price at effectively nothing and eliminates any possibility of scarcity. There is no market story here beyond that. If a listing is charging meaningfully for dwarf whites, it is charging for shipping and convenience, which is fine, but know what you are paying for.
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## Spiders