Who is male, and who isn't, and does it matter anyway ?

It is generally accepted to be very difficult to accurately know the sex of your spiders. When they are very young, it is all but impossible to tell. However, as they grow, there are 2 accepted ways to tell who is male and who is female. These are listed below, with some discussion about each method.

A question that is often asked is 'why does it matter?' For me, it doesn't matter at all, but the biggest reason it might do to other keepers is the vast difference between the usual lifespans of tarantulas between males and females. Secondary to this might be the difference in the habits of male spiders, who sometimes feel the need to wander when they reach maturity, which might increase escape attempts.

In general, female spiders drastically out-live their male equivalents. Females of the slower growing species like Brachypelma can live up to around 25 years. For the males, life is nothing like so long, and even in these slow-growing species, estimated lifespans do not reach even half that of the equivalent female. For this reason, most keepers will prefer to keep female spiders, and most pet shops will happily lie to their customers about the sex of spiders for sale. If you see any animal that is marked 'confirmed female', treat this with a high level of suspicion - there is around a 50% chance that they will be wrong.

Sexing by studying the exuvium

John and Kathleen Hancock, in their book "Tarantulas: Keeping and Breeding Arachnids in Captivity" demonstrate a very useful technique for accurately sexing tarantulas. This involves studying the most recent exuvium of a spider under a stereoscopic light microscope.  This is of zero help in a shop situation when none of the equipment necessary is likely to be at hand, but remains a worthwhile technique nonetheless, especially for tarantula breeders, some of whom will consider acquiring and using this equipment essential to their enterprise.

Sexing by epiandrous fusillae

In 1967, a very interesting article was written and compiled by B. J. Marples entitled "The Spinnerets and Epiandrous Glands of Spiders". It was noted here that almost all male spiders have an extra component to their spinnerets which allows for the male-specific task of spinning a sperm web. At last, if we could find the spinnerets on a spider, there was some hope of reliably identifying its sex. I could go into detail about the differences between male and female spinnerets, but for the purposes of this article it is not necessary, and perhaps overly scientific for the diaries to get into...

General other signs

In addition to the two previously mentioned reliable methods, there are some other 'pointers' which may help suggest the sex of your growing spider. However, please note these are not accurate, involve much observational guesswork, and should absolutely not be relied upon in any situation where having the right sex of spider is vital. I provide them here, simply because they are all significantly easier to implement than any of the scientific techniques above, and might help as a general guide or in some other small way.

And that really is as much help as I can give you - not much is it ?!

Below is a table of the spiders I currently keep, or have previously kept, together with my best guesses so far about what sex they are, or were. As I said at the top of this article, I couldn't care less, and find that the joy of keeping male spiders is equal to that of keeping females. The ONLY disadvantage I can see is that I will be upset earlier, when the males reach the end of their lifespans. Because I try and raise my spiders from very young (as close to birth as possible in fact), I will still get to spend a great deal of time with each animal, and have the additional reward that comes from watching and nurturing an animal from its earliest stages of life to it's last. 

The Spider Diaries 'guesstimate' sex list

Now, in the diaries, you will see that I refer to most, if not all of my animals as 'she' or 'her'. I view this rather as a term of consistency and convenience, rather than as a factual reference to what sex they may or may not be. The truth is - I just don't know in the vast majority of cases. Of the 3 confirmed spiders above, I KNOW that Legz is male because he has reached his final moult, and his pedipalps have changed shape and function, making it obviou, same goes for Fluffy, and I KNOW that ZBD is female because she has moulted 3 times in my care, all at adult size, and has shown no sign at all of slowing down, or having problems. Male spiders do not usually moult again after their maturation moult, and if they do, they tend to have problems doing so, one of which is extrenely likely to lead to their deaths.

And there concludes our brief foray into the sex of spiders...