It's right next to the water dish as well as in the hide so possibly a moisture issue?Hi
Some pics of enclosure and what species you keep in it will help us advice you better.
Mould in general while unsightly is not an issue.
It might indicate other issues like not enough ventilation on the enclosure or too much moisture in substrate.
Regards Konstantin
Thank youHi
don't see anything concerning. She will clean the hide when she feel like it.Other bits you can pick out when you do maintenance.Its not dangerous to your pet but if you see its getting out of let the substrate dry out a little
Regards Konstantin
Thank you so much )Move the water bowl around. Like that you are not overflowing the water bowl in the same place every time. Plus the substrate dries out completely where you have over flowed it.
Moving the water bowl around also helps with humidity levels. As you end up with one area that was moistened last week, or the week before & another that has just been lightly moistened this week.
Another helper when it comes to mold are springtails. They are no good in dry enclosures, as they need moisture. But I keep a separate tub of spring tails & if I start to get mold, even in a desert species enclosure, I can add a small (5ml) teaspoon full of springtail substrate in & the mold is then eradicated.
Most tarantula suppliers have springtails available.
https://www.thespidershop.co.uk/product/spring-tail-culture/
Edited to add. I add dried yeast to my higher humidity enclosures, to keep my springtails well fed & multiplying. As yeast creates mold which feeds my springtails. So I intentionally cause mold in some of my enclosures.