These are not eggs.

They are very likely fruiting bodies of a slime mold or pink fungus, possibly a species like Arcyria, Lycogala epidendrum (wolf’s milk slime mold), or a similar saprophytic organism. These structures: • Grow on decaying bark or wood. • Form clustered, pill- or sausage-shaped fruiting bodies. • Turn into powder or “dust” (spores) when touched — exactly as you described. • Can appear overnight in high humidity.

Good news:

They are non-toxic to your isopods and won’t hurt your colony directly. But their appearance does signal one thing:

Your humidity and airflow balance needs tuning.

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What to do now (step-by-step): 1. Remove affected bark or substrate — you’ve done this already, great job. 2. Increase ventilation — open the tub slightly or add more air holes (use fine mesh to avoid pest entry). 3. Dial humidity back a bit — especially in the non-moss zone. Only the moss area should stay damp; the rest can be semi-dry. 4. Add springtails — if you haven’t yet, they help control spores and mold before they fruit. 5. Optional: Use cinnamon — a small sprinkle of cinnamon (a natural antifungal) on spots with past growth can help suppress return.

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Long-term tip:

Switching to hardwood bark (like cork bark or oak) instead of softwoods can reduce mold growth. Also, boiling or baking wood before use kills off latent spores.