For the next three to six months, the female continues life as usual, though she should be fed more heavily if possible to help her build up food reserves before laying. Eventually she will construct a loose web in her burrow and either molt or lay eggs. If she molts, the sperm are cast aside with her old exoskeleton, and she can no longer lay fertile eggs. If instead she comes out without molting and rolls the web into a stiff (usually oval) case then she has laid her eggs.
Tarantulas may lay from less than a hundred (Theraphosa spp.) to more than a thousand (Citharischius spp.) eggs in a clutch, with no obvious correlation between clutch size and age of the female.
Normally, females guard their egg cases by hovering over them, protecting them from attacks by ants, other spiders, predatory insects, and possibly fungus. If stressed, the female may rip open the case and eat her eggs (which admittedly are a good food but certainly not the result you are looking for), so, leave her alone as much as possible. A guarding female usually continues to eat (some keepers withhold food to prevent insects disturbing the case) and otherwise behaves fairly normally. If the egg case is hung in a dense web placed within the burrow and not protected under the body of the mother, the female may become even more aggressive than normal. Each day the mother rotates the egg case several times, equivalent to a hen turning her eggs.
If you leave the egg case with the female, you will notice after about six weeks that the case has been torn apart and the eggs are missing. If you look carefully, you should notice at least some spiderlings in tiny burrows scattered over the cage bottom, where they probably will die because you will not be able to feed them or even separate them from the mother. For this reason, most breeders corner the female after she has cared for the case for a month and remove the egg case to a separate container, where it can be watched and the young rescued immediately. Remember that mother tarantulas may be exceptionally aggressive.
Generally the egg case is placed in a small plastic cup (such as a cup used for delicatessen salads) with a cover to keep the humidity at 65 percent. Roll the case at least three or four times a day. In about two weeks, the eggs should be six weeks old and, for most species, near hatching. Carefully slit the case open with small scissors and pour the contents into a shallow covered dish (such as a petri dish) with a circle of laboratory filter paper on the bottom. The eggs may be in any of three or four stages of development. Some will be simply round cream to brown eggs that are still far from hatching. Others (perhaps the great majority) will be postembryos, which look like an unmoving hump holding on to the egg with partially developed legs. The postembryo cannot move and is still using the yolk of the egg to continue development. If kept clean and at about 65 percent humidity, these will continue to develop into spiderlings.
In many cases, most of what is released from the egg case will be first instars, which look like pale, often transparent, little spiders that can move around and feed. These generally molt within a few days into second instars, which have more substance and often the beginnings of a color pattern (which seldom comes close to that of the adult). At this point, the yolk sac has been absorbed and the spiderlings are distinct little individuals.