I use a bit of cork bark in all my spider tubs. Usually with a bit of plastic plant or something. The smaller ones have the film tub still in there too. I had an offcut bit of branch and the red knee seems to like perching on it. Weird spiders

The red leg burrowed like crazy, so when I put her in a bigger tub I gave her a deeper substrate. Shored it up with branches so it wouldn't collapse, and she hasn't dug a single millimetre.

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Snickers
Snakes - Carpet Pythons1.1 Bredl's Python (Neville/Luna)1.1 Jungle X Carpet Python (Molly/Arthur)0.1 Diamond X Carpet Python (Aurora)
Inverts - Tarantulas0.0.1 B. bohemi - Mexican Fireleg (George)0.0.1 B. emilia - Mexican Red Leg (Ginny)0.1.1 B. smithi - Mexican Red Knee (Fred/?)0.0.1 B. vagans - Mexican Red Rump (Charlie)0.0.1 C. fimbriata - Indian Chevron (Snape)0.0.1 C. cyaneopubescens - GBB (Mosag)0.0.1 E. sp. "blue femur"0.2.0 G. rosea - Chile Rose (Aragog/Junior)0.0.1 L. parahybana - Salmon Pink Birdeater (Hagrid)