The propagnation of tarantulas is very similar to the propagnation of other spiders when it comes to the method of fertilization and all species lay eggs. However, there are some differences: tarantula males stay about the same size as the females. In many other spiders the males remain much smaller. The breeding season is dependent on the species and often depends on the geographical distribution of the species.
Tarantulas are invariably solitary animals who only visit each other in the propagation time to mate and produce offspring. Tarantulas are sensitive to pheromones, which many arthropods and insects provoke each other, but traces by stridulation and vibrations to produce another. Stridulation is making noise by rubbing hardened body parts together, with a sjirp-like sound is produced, similar to other stridulating animals, such as crickets and cicadas. The stridulation organs of tarantulas are located on the chelicerae and the first segment of the pedipalp.
Like other spiders the fertilization is external. The male creates a spermaweb which consists of a web on the bottom and a second web which floats as a hammock on the bottom web. The spermaweb only serves to help the male to get sperm in the right place. The male crawls on his back under the hammock and deposits a drop of sperm on it. The sperm is secreted by the genital opening of the spider, which is located on the underside of the abdomen, also called epigyne. Next up he crawls back at the top of the web and sucks up the drop of sperm with his bulbus pedipalps. After he is done, the spermaweb will be destroyed. Now the bulbus pedipalps of the male are 'loaded' he can mate with a female whereby he shouldn't wait too long because his fertility will reduce after about six months.
When a male has found a female the mating occurs. The male makes rhythmic drumming movements with his legs. The drumming is species-specific and needed to let the females know that there is a partner in the neighborhood. If she is interested she lets them approach whereby the male pushes her back with his legs. The female gets in some kind of trance and the male can make contact with the genital opening of the female. This is just like in males located on the underside of her abdomen. Since the bulb of the male body has a specific form will only fit into the genitals of females of the same species, which prevents intersections. The female stores the sperm in the seminal vesicles until the fertilization is complete. Like other invertebrates sperm comes into contact only with the eggs when they are dropped off and leave the body of the female. If a female molts before the eggs are deposited, the seminal vesicles will be renewed and the sperm will be lost.
Depending on the species of the female tarantula after some time a cocoon is formed, a white ball with a silk-like outer layer, filled with eggs. The number of eggs is species-dependent, some tarantulas put off several dozen eggs , others can produce up to 2000 per cocoon. Some species (Heterothele) are known to produce a second cocoon or even a third cocoon, but this is exceptional.
Tarantulas fiercely defend their eggs, the egg sac is usually guarded by the female. Underground living species often close their cave tight, while wandering species carry the cocoon with them. After several weeks the eggs start to hatch, but the nymphs remain in the cocoon for another while. This stage is called the first nymphal stage, but actually the young tarantulas are between the embryo and the nymph stage, they look like eggs with legs and have a hard time moving, they have a very large abdomen and barely developed legs and mouthparts. At this stage, the nymphs are very vulnerable. Only when they are molted the first time they appear anatomically like the parents though they are usually lighter and are still hairless. In most species the tarantulas come out of the cocoon in this stage. Depending on the species and temperature of incubation, the cocoon will hatch after one and a half to three months. However, the nymphs remain together until the next molt, while they are monitored by the mother.
After the second molt the tarantula got hairs (setae) and the legs and mouth parts are thicker and clearly segmented, the abdomen is smaller. The young tarantulas start to look like their parents, even though their colors are aberrant. The spiders are called spiderlings at this stage. They are usually less than a centimeter long and will start eating for the first time. The juvenile tarantulas leave the nest in search of food and parental care of the mother comes to an end.
The largest number of spiderlings, more than 95 percent, usually dies within a short time, by being eaten by a wide range of predators. As a general rule, the greater the tarantula is, the less enemies it haves.
