What difference does sex make?
In Brachypelma boehmei, the main differences are lifespan, maturity and adult behaviour. Juvenile males and females can look very similar.
Mexican Firelegs grow at a slow rate and reach about 14–16 cm (5.5–6.25 in). Size alone does not reliably tell you whether a juvenile is male or female.
Lifespan
Male Brachypelma boehmei are generally expected to live roughly 4–6 years, while females can live 20 years or more because they continue moulting after maturity.
A confirmed female Mexican Fireleg is usually a much longer commitment. A mature male may already be in the final adult stage of his life even if he looks healthy and active.
Sexing from a moult
The most dependable way to sex a juvenile Brachypelma boehmei is from a suitable moult. The exuvia needs to be large enough and intact enough to inspect the relevant structures.
Ventral sexing can sometimes give clues with a larger Mexican Fireleg, but photographs and markings can be misleading. If the view is unclear, wait for a better moult rather than forcing a definite answer.
What changes when a male matures?
After the ultimate moult, a male Brachypelma boehmei often becomes more active. He may spend more time walking around the enclosure and show less interest in food.
A mature male Mexican Fireleg can also look leggier and slimmer through the abdomen than an adult female. Use species-specific adult male features together with moult history.
Does a female need different care?
Male and female Brachypelma boehmei do not need different basic husbandry. Both sexes need the same enclosure style, water, ventilation and temperature for the species.
A mature male Mexican Fireleg may pace around a previously suitable enclosure. That behaviour does not automatically mean the setup is wrong.
Temperament and sex
Sex does not reliably predict temperament in Brachypelma boehmei. One individual can be calm during maintenance while another reacts more quickly, regardless of whether the spider is male or female.
A mature male Mexican Fireleg may seem more restless because he walks more, but restlessness is not the same thing as aggression.
Buying male, female or unsexed
A confirmed female Brachypelma boehmei often costs more because the sex is known and the expected lifespan is much longer. A confirmed male can still be a good choice if the shorter lifespan suits the keeper.
If you buy an unsexed Mexican Fireleg, be prepared for either outcome. Keep moult dates and save suitable exuviae so the sex can be confirmed later.