Size and growth
Adult Aphonopelma anax reach about 15–18 cm (6–7 in) and are slow growers. Adult Aphonopelma seemanni reach about 14–16 cm (5.5–6.25 in) and are slow growers. That affects how quickly Texas Tan Tarantulas and Costa Rican Zebras move through sling and juvenile enclosure sizes.
Do not use size alone to estimate age in either Aphonopelma anax or Aphonopelma seemanni. Sex, feeding and individual variation can change the pace of growth even when two spiders began at a similar size.
Enclosure and lifestyle
Texas Tan Tarantulas are terrestrial, while Costa Rican Zebras are terrestrial. Build the Aphonopelma anax enclosure for a terrestrial spider and the Aphonopelma seemanni enclosure for a terrestrial spider instead of assuming two tarantulas need the same shape of setup.
For Aphonopelma anax, substrate depth, retreat position and usable space should match its terrestrial lifestyle. Apply the same rule separately to Aphonopelma seemanni; the enclosure should make normal behaviour easy rather than forcing either species into a generic layout.
Temperature, water and moisture
A practical temperature range for Aphonopelma anax is 19–26°C; for Aphonopelma seemanni, it is 20–25°C. Stable room conditions are more useful for both species than chasing small fluctuations within those ranges.
For Aphonopelma anax, keep a mostly dry setup with with a water dish; maintain a modest moisture gradient for juveniles. For Aphonopelma seemanni, use provide a water dish and a moisture gradient rather than keeping the whole enclosure wet. In both enclosures, keep fresh water available and adjust substrate moisture to how quickly the setup actually dries.
Temperament and maintenance
Aphonopelma anax is a New World species, while Aphonopelma seemanni is a New World species. That background is useful when planning maintenance, but individual Texas Tan Tarantulas and Costa Rican Zebras can still differ noticeably in speed and defensiveness.
With both Aphonopelma anax and Aphonopelma seemanni, locate the spider before opening the enclosure, use long tools when they make the job safer and keep a catch cup ready for rehousing. Handling is not required for routine care.
Male and female lifespan
Male Aphonopelma anax generally live roughly 5–7 years, while females can live 20 years or more. Male Aphonopelma seemanni generally live roughly 4–6 years, while females can live 15–20 years.
Those lifespan ranges make sex particularly relevant when comparing Aphonopelma anax with Aphonopelma seemanni. A confirmed female of either species is normally a much longer commitment than a mature male, and the exact age of an older juvenile may be impossible to know.
UK availability and trade notes
In the UK hobby, Aphonopelma anax is currently classed as uncommon, while Aphonopelma seemanni is classed as common. Stock changes between specialist sellers, captive-produced batches and show weekends, so availability should be checked at the time of purchase.
For records and purchases, use the scientific names Aphonopelma anax and Aphonopelma seemanni as the main identifiers. Current trade notes list Aphonopelma anax as 'Check current CITES rules before cross-border trade' and Aphonopelma seemanni as 'Check current CITES rules before cross-border trade', so check current requirements before any international movement where controls may apply.
Practical difference in day-to-day care
The practical difference between Aphonopelma anax and Aphonopelma seemanni comes from the combination of lifestyle, adult size, growth and moisture needs. Those factors change how much substrate, vertical space and maintenance access each enclosure needs.
Whichever species you keep, let the individual spider settle into an enclosure designed for its own biology. That applies equally to Aphonopelma anax and Aphonopelma seemanni: fresh water, secure housing and patient observation matter more than trying to make the two species behave the same way.