Size the enclosure to the spider now
Choose the Brachypelma auratum enclosure for the spider's current size, not the maximum adult measurement. The spider should be able to find prey, water and its retreat without being lost in unused space.
As a Mexican Flame Knee grows, increase enclosure size in sensible stages instead of jumping straight from a sling tub to an adult display.
Lifestyle changes the shape
Because Brachypelma auratum is terrestrial, enclosure proportions should support that lifestyle. Floor space, height and substrate depth are not interchangeable.
The right dimensions for Mexican Flame Knees are therefore about usable space, not simply litres or centimetres on a product label.
Fall distance and hard decor
For Brachypelma auratum, keep fall risk in mind when deciding how much open height sits above the substrate. Heavy-bodied terrestrial spiders especially should not have a long drop onto hard decor.
Keep stones and heavy cork secure in the Mexican Flame Knee enclosure and position them so normal digging cannot create a dangerous landing area.
When the enclosure is too small
Rehouse Brachypelma auratum when the retreat no longer fits, required substrate depth is compromised or routine access to water and feeding has become awkward.
A Mexican Flame Knee touching a wall is not, by itself, proof that the enclosure is too small. Look at how the whole setup functions.
Prepare the next size first
Set up the new Brachypelma auratum enclosure completely before the move. Add substrate, retreat and water, then check ventilation and security.
Moving a Mexican Flame Knee into a finished enclosure keeps the transfer short and avoids trying to adjust decor while the spider is exposed.