How fast does it grow?
Mexican Red Knees are generally described as slow growers. That gives a useful expectation for Brachypelma hamorii, but it is not a promise that every sling will reach the same size at the same age.
Adult Brachypelma hamorii reach about 14–15 cm (5.5–6 in). The time taken to get there depends on sex, feeding, temperature and ordinary individual variation.
Moult intervals change with age
Small Mexican Red Knees often moult more frequently because they are growing rapidly. As Brachypelma hamorii gets larger, the interval between moults normally becomes longer.
Do not treat a longer interval in an older Mexican Red Knee as a problem by itself. Look at appetite, body condition, retreat use and the spider's previous moult pattern.
Feeding and temperature
Feeding influences how quickly Brachypelma hamorii grows, but there is no benefit in keeping the abdomen constantly overfilled. Offer suitable meals and let appetite guide the interval.
A practical temperature range for Brachypelma hamorii is 20–25°C. Stable conditions are preferable to pushing the temperature upward in an attempt to force faster growth.
Male and female growth
Male Brachypelma hamorii usually mature sooner and have a shorter lifespan of about around 6–10 years, while females can live 20–30 years. That difference means two similar-sized juveniles may eventually follow very different timelines.
Sex cannot be judged reliably from growth speed alone. Use a suitable moult when possible instead of assuming a faster-growing Mexican Red Knee must be male.
Tracking growth
Record moult dates for Brachypelma hamorii and note approximate size when rehousing. You do not need precise measurements after every moult; a simple record is enough to show whether the spider is growing steadily.
Photographs taken after a Mexican Red Knee has hardened can also help show changes over time, provided the spider is not disturbed simply to get a measurement.
When growth means rehousing
Rehouse a Mexican Red Knee when its current enclosure no longer gives enough retreat space, substrate or safe access for maintenance. Do not move Brachypelma hamorii after every moult automatically.
Prepare the larger enclosure before the transfer. The goal is to keep each stage of Brachypelma hamorii's growth in housing that is secure and practical, not to race toward the adult enclosure.