Size the enclosure to the spider now
Choose the Aphonopelma bicoloratum 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 Blood Leg grows, increase enclosure size in sensible stages instead of jumping straight from a sling tub to an adult display.
Lifestyle changes the shape
Because Aphonopelma bicoloratum is terrestrial, enclosure proportions should support that lifestyle. Floor space, height and substrate depth are not interchangeable.
The right dimensions for Mexican Blood Legs are therefore about usable space, not simply litres or centimetres on a product label.
Fall distance and hard decor
For Aphonopelma bicoloratum, 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 Blood Leg enclosure and position them so normal digging cannot create a dangerous landing area.
When the enclosure is too small
Rehouse Aphonopelma bicoloratum when the retreat no longer fits, required substrate depth is compromised or routine access to water and feeding has become awkward.
A Mexican Blood Leg 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 Aphonopelma bicoloratum enclosure completely before the move. Add substrate, retreat and water, then check ventilation and security.
Moving a Mexican Blood Leg into a finished enclosure keeps the transfer short and avoids trying to adjust decor while the spider is exposed.