As far as we are aware tarantulas do not change gender. It is possible to sex tarantulas from quite a young age, and once the gender has been identified this does not change during the lifetime of the spider.
The only potential issue with sexing immature tarantulas is that the process requires a degree of skill and experience – not to mention a microscope. There have consequently been cases where tarantulas have been identified incorrectly as a certain gender, only to end up being something totally different.
In most cases, reputable tarantula suppliers can be trusted to supply appropriately-sexed tarantulas. For example, if I sell a tarantula as a specific gender then it will have been sexed at least twice. If I am at all uncertain then the tarantula will be sold as “unsexed” to avoid any disappointment in the future.
How Do You Tell a Male Tarantula From a Female?
The only guaranteed way to tell the gender of an immature tarantula is by inspecting a moulted skin under a microscope. When the tarantula moults it also sheds the lining of the reproductive organs, and these can be observed under a microscope to ascertain the gender of the spider.
While there are other methods that are regularly touted on forums, such as the appearance of the epigastric furrow, these methods are inaccurate at best. They require a very experienced eye, from a keeper that has kept large numbers of spiders and is familiar with the species in question. Even then mistakes can occur.
A small number of tarantulas will display differences in color or patterning before reaching maturity. For example Poecilotheria ornata males can look subtly different from females. Singapore blues may also appear rather different as they develop.
It is important to state, however, that the ability to visibly identify the gender of a tarantula is difficult and mistakes are made.
Assuming the tarantula is not mature then sexing via sloughed skins is really the most effective method by a long way.
Are All “Unsexed” Tarantulas Actually Male?
It is sometimes suggested on forums and on social media that any decent-sized tarantula that is offered for sale without a gender is likely to be a male. This is because most hobbyists seek out the longer-lived female tarantulas.
It has been suggested that some unscrupulous breeders sex their spiders, selling the females clearly labelled as such. The males, however, are sold as “unsexed” to avoid reducing their value to potential buyers.
While there may be a small amount of truth to this, it is generally quite unlikely for two reasons. Firstly, the better-known and more reputable tarantula traders appreciate the importance of a strong reputation. If one of these well-known retailers behaved in this way word would quickly get around. And a reputation, once destroyed, is not easy to rebuild.
There is another reason too. Female tarantulas are easily identified due to the spermathecae visible under a microscope. However males are identified by the lack of this organ. Therefore it is easier to be certain that a tarantula is a female rather than a male.
Tarantulas have a nasty habit of chewing up their old skin after moulting. The skins are also very fragile. Therefore it is entirely possible that even with a sloughed skin, there is too much damage to be able to properly identify the gender.
In these cases it is safer to list the spider as “unsexed” than to take a punt and risk an unhappy customer down the line.
Do Male or Female Tarantulas Live Longer?
Female tarantulas will live much longer than males. This is why female tarantulas are in particular demand, and tend to command higher prices than males. While a male tarantula is likely to only live for a year or so after reaching maturity, the females can live for 8-20 years or more depending on species.
Are Female Tarantulas More Aggressive Than Males?
I currently have over 200 tarantulas in my collection, spread across a wide range of species, and can honestly say I have seen no difference in aggression levels between males and females.
Do Adult Male Tarantulas Look Different to Females?
Adult males are quite obviously different to females. They tend to be smaller, slighter and more “wimpy” looking.
When they reach maturity their pedipalps develop special adaptations for mating. These are typically known as “palpal bulbs” and are quite easily spotted on the tarantula.
Lastly lots of adult males develop hooks on their front legs, which are used to hold the females fangs out of the way during mating.
When Do Male Tarantulas Get Hooks?
Male tarantulas only get hooks when they pass their final (ultimate) moult and reach maturity.
Note, however, that not all tarantula species possess these tibial spurs at maturity. As a result it’s important to check whether the species you’re keeping does develop hooks before using it as a guaranteed way to identify an adult male tarantula.