Spiderman or Spiderwoman: Determining the Sex of Your Tarantula

One of the components of the successful breeding of tarantulas is their early sex determination. Males of spiders mature much earlier than females, so by the time when females mature, they already lose the ability to reproduce, as a result of which synchronization of individuals of a different sex from one cocoon is not possible. When it comes to popular spiders, this is not a problem, you can always find a younger male and grow up, but there are also such types of bird spiders that are quite rare on sale and it would be a pity to miss the opportunity to get offspring from them. If one learns to determine the sexual identity of the spiders at the first ages and to create the appropriate conditions for individuals of different sexes in the future, then it may happen that both sexes mature at the same time. In order to obtain such synchronization, females should be fed more abundantly than males, while keeping at a temperature that will be somewhat higher. These conditions do not guarantee that the female will mature by the time the male becomes mature since such cases have been noted that even under more favorable conditions for growth, the females do not want to molt, and the males (although kept in stricter conditions) molt in leaps and bounds.

How to Determine the Sex of a Spider?

Spiderman or Spiderwoman

Determining sex by exuvial

The most accurate method for determining the sex of tarantulas is a method that relies on studies of the spider (freed skeleton) exuvium. Thanks to this method, you can determine the sex of a spider at first ages.

Adults or bred individuals:

In order to determine the sex using this method, it is necessary to unfold the lower part of the abdomen of the spider exuvium. Pay attention to the area between two white spots located closer to the base of the abdomen. This and another pair of similar spots determine the stigmatic disposition of the lungs of the tarantula. Genitals are located in the area between the first pair of stigma. In females, there is a trace of spermatheca (seed receptacle) in this area. In different species, the form of spermatheater of tarantulas varies but, despite this, it is well expressed and it can be easily noticed. The males have a flat surface in this area. If the exuvium is dry – it can be soaked in alcohol or hot water.

First-age spiders:

In order to determine the sex of a tarantula using this method in spiders of early ages, you will need a microscope or binocular, good lighting, a few needles, a napkin, alcohol and some kind of dye – it can be fuchsin, you can buy a bottle of iodine in a pharmacy.

You’d better extract an exuvium from the volume of the spider immediately after the molt, while at the same time try not to disturb the newly faded individual since the spiders are quite vulnerable in the first hours after the molt. After the exuvia is extracted, the necessary part should be separated – this is the lower part of the abdomen. Then we take a piece of glass from a microscope, add a drop of alcohol on the prepared part of the exuvium. Then we need needles, with the help of which we must try to straighten chitin. Do not be upset if you did not manage to straighten an exuvium or you accidentally damaged it – you will learn to straighten it with time. After the shell is straightened, you need to remove the excess alcohol with a napkin, gently soaking the sides around the exuvium first, then the exuvium itself. Then, we take a dye and drip a droplet on the area we use (the gap between the bottom of the first couple of stigmas), after which we must once again use a napkin. Now you can look under the microscope: if this female, then the spermatheca will paint over much brighter than the rest of the area and will be clearly visible.

Do not forget that using this sex determination method in spiders of the first ages, you will need a lot of patience since the process of straightening the exuvium can take a lot of time. In addition, it often happens that the spider had time to chew the pollinated shell, thereby causing it to become unusable. In addition to all of the above, you may need a catalog of spermatheca of tarantula spider females since spermatheca of different species can vary greatly in shape.

The use of alcohol is mandatory, even if the molt is fresh and does not need to be soaked, because the molt will be rolled up and turned over on the opposite side when using water.

Without the dye, the spermatheca will merge with the main background, thereby not being visible to the eyes.

It is also necessary to remove the residual moisture with a napkin, otherwise, the dye will dissolve in alcohol and not directly dye the molt itself.

Determining sex by male epianral glands

This method is also considered to be quite accurate since it is based on a scientific approach. This is the only exact method for determining a spider in the living specimen. In addition, it does not require an exuvium, which can be obtained only after a spider molt. When checking the spider apparatus of tarantulas, you can see that only males have special spider glands in the epiginum area. Near the epigastric sulcus, there are the appendages of these glands, which are barely opened with holes. These holes have a round or triangular shape and are located in 2-4 rows. The area of these holes can be identified by thick short and darker hairs, which form a kind of arch. These appendages are used by males when weaving a spermatic reticulum, so if they are found in a spider, then this individual is a male, but if they are not found, then it is a female.

These appendages have some similarities with the main spider legs (spinneret) and are called epiandrous fusillae (epiandral glands).

To accurately determine the sex of a spider using this method, you should have a trained eye and several heterosexual specimens for comparison. In addition, you must learn to carefully handle the spiders so that the spider can be taken in hand and explored. It is most difficult to determine the sex using this method in the following types of spiders: Aphonopelma seemanni, Megaphobema robustum, Nhandu coloratovillosus, therefore you’d better gain experience on spiders that have dark hair coloring, indicating the location of the appendages.

“Complex” method for determining the sex

This method of determining the sex of a spider-tarantula appeared later than the two above and is considered not so accurate, but still, when comparing a group of spiders, it is possible to determine with a high probability which sex a particular spider belongs to. You need to have a group of spiders when using this method since it is based on comparing a number of features in opposite sexes:

  • the shape of the epigastric groove;
  • the distance between the first pair of stigmas;
  • the angle of the first pair of stigma.

The female epigastric groove has a more curved shape compared to the male, while the male epigastric groove is almost a straight line between the first pair of lungs.

The distance between the first pair of stigmas: females’ lungs are located at a greater distance from each other; in males, the lungs are closer to each other.

The angle of inclination of the first pair of stigmas in females has a greater degree and is not less than 20°, while in males the lungs are more horizontal, the angle of inclination does not exceed 5°.

Determining sex by size and shape of fangs

Determining the sex of a tarantula by its shape and size is one of the most inaccurate methods, but despite this, it should not be excluded. It can be used in conjunction with the above methods to increase the percentage accuracy. Female chelicera are massive, wider and more powerful, widened at the base and slightly narrowed at the end. The male chelicera, in turn, are thinner and not so wide, in addition, they are more uniform along the entire length from base to tip. This difference in size and shape is clearly visible in adults, but, unfortunately, is insignificant in adolescents. Therefore, when using this method, it is necessary to have a group of spiders, preferably of the same size. The author of this method, Dr. Robert Gale Brine the Third, claims that using this method successfully determines the sex of immature individuals of the genera Aphonopelma and Brachypelma. It can also be assumed that this method is applicable to spiders from other genera since the chelicera of male adults of all species is smaller.

There are other methods for determining the sex of tarantulas but they are not significant, so we will only mention them:

  • the ratio of abdomen and cephalothorax (acron);
  • the ratio of the proportions of the length of the legs relative to the body;
  • slight differences in the pedipalps;
  • growth rates: females tend to grow slightly slower than males, so it can be concluded that most of the largest individuals are males. At the same time, it is important that all the studied individuals are kept in the same conditions and do not have any pathologies.

Virtually all the methods listed are based on sexual dimorphism of tarantulas. Most adult spiders of the same species can have different colors, shapes, sizes and body proportions. The ratio of the length of the legs relative to the body is most noticeable. In addition, males get bulbus and tibial spurs after definitive molting. In individual species, this difference is already noticeable at an earlier age. For example, in Poecilotheria, Ephebopus, the difference in the ratio of legs and body of different sexes can be seen at earlier stages. In spiders from other genera, this difference may not be noticeable at all. For example, if we compare Nhandu coloratovillosus, we can hardly find any differences in heterosexual individuals.

Thus, sexing a spider-tarantula is a very useful skill!

Category: General Issues

Tags: biology, insects, nature