How do I know if a male is mature?

The most reliable way of checking if a male tarantula is mature is to examine the last segment of the palp.  If this has a palpal bulb on its underside the male is definitely mature.  If the end segment of the palp looks similar to the tarsi of the legs then, either your male is immature or you have a female.

Most mature male tarantulas also have spurs on the underside of the tibia of leg I.  Immature male and female specimens never have these spurs.  Note that male Poecilotheria, Heteroscodra, Stromatopelma and Citharischius do not have tibial spurs.

When is a mature male ready to mate?

The male matures once it completes its final moult, but it won’t be ready to mate immediately.  It is best to wait until you see your male pacing about in its tank.  This is a sure sign he is looking for a female.  By this stage the male will have produced at least one sperm web on which he deposits his sperm.  The sperm is then taken-up by his palpal bulbs.

If your male has mated with a female you should wait several days before trying to mate him again.  This will give him time to recharge his palpal bulbs with sperm.  You can also watch out for fresh sperm web remains (a thick white string of silk).  If you find one he is ready to mate.