Tescos
12-29-2006, 07:29 AM
A Little help with Sexing
By Chris Sainsbury
*This article is reprinted with the permission of Chris Sainsbury (Tescos) and The British Tarantula Society (thebts.co.uk). This article was originally printed in the BTS Journal, Issue: November 2006, Vol. 22 No. 1. Just one of many reasons to join (http://thebts.co.uk/faq.htm) this great organization.
Introduction
I’m writing this article mainly due to the number of posts on internet web sites where the poster is asking about what sex his or her tarantula is based on a photo of its shed exuvia. Although many of the replies to such posts are often correct, they often don’t go into the reasons why they say it is a female or a male except by saying that they can or can not see a flap. My aim here then is to try and explain some of the key parts of the male and female exuvia when it comes to sexing them correctly and to try and provide some useful hints and tips to help you in the process of sexing your own tarantulas.
What and where?
Theraphosid spiders can normally be accurately sexed by a shed moult from the 5th-6th moult onwards. I have found some species can be sexed one or two moults before or after this stage but it is often an educated guess when sexing specimens before the 5th moult.
The main `trick´ to sexing theraphosids, is having the knowledge of where to look and what exactly you are looking for on a moult.
This might seem quite obvious, but it is surprising what mistakes can be made by not understanding some of the structures that you might see when looking at an exuvia under a microscope or even with the naked eye.
Figures 1 & 2 (below) show the relevant key features of a female and male moult respectively. These labeled features are listed below with their functions.
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/femaleepigynumfig1copy.jpg
Fig 1
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/Maleepigynumfig.jpg
Fig 2
Arthordial membrane; shed muscle attachments that mark the limits of the epigiynum area on the left and right.
Slit sensillum; small button hole like stress detectors that can be found in the upper alcove.
Upper alcove; forms the nose of a females epigiynum area and is where you will find the females spermatheca.
Spermatheca; found only in female theraphosids, this is the place where a males sperm is stored after mating. It develops from a paired structure but can form into pared or fused organs and is located in the lower half of the upper alcove behind the uterus externus that it extends off from.
Uterus externus; a thin often transparent pocket like membrane found only in females, the opening of which is called the gonoslit. It is the only part of the uterus that is shed during a moult and joins to the uterus internus and leads to the oviduct and ovaries, but these of course are retained by the tarantula during a moult..
Gonoslit; this is the opening to the females sexual organs that can be found in the epigastric furrow.
Epigastric furrow; this is located on the underside of the abdomen between the two anterior book lungs. It is a fold in the skin that’s leads to the gonoslit or in the male’s case, the gonopore.
Bursa copulatrix; often called the lower alcove; this is where it is said eggs and sperm mix during egg laying.
Antererior book lungs; these are the two front most feathery type lungs nearest the cephalothorax that the spider uses to breath.
Gonopore; this is the opening to the males sexual organs. In a moult it appears small and buttonhole like with thick lips.
Male epigastric organs; found only in males these organs produce a liquid that mixes with the sperm (recently found out they may also/or be slilk glands use in sperm web production). They can be mistaken for spermatheca especially in smaller moults if you’re unsure what they look like.
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/Lasiodoraparaybanaspermathecafig3co.jpg
Fig 3
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/Brachypelmaaugustummaleorgansfig4co.jpg
Fig 4
In figures 3 and 4 you can see that male epigastric organs differ from a spermatheca in the way of looks by having a base that is much narrower than the body or head of the structure. In the majority of cases they resemble small mushrooms or child like drawings of trees but in small moults they can very much resemble a developing paired spermatheca which can cause some confusion.
These in smaller moults tend to be situated quite close to and to either side of the gonopore but as the moults get bigger I have found that their position tends to move outwards but still based at the same base line as the gonopore.
Spermatheca on the other hand, have a base that is typically as wide as or wider than the body or head. In cases like this where you may be unsure if it’s one or the other there are other certain features to look for. The big clue then would be to see if it has a uterus externus and to study the size of the gonopore. If a uterus externus is not present then you will know you have a male on your hands, also the small gonopore will confirm this if it is very small.
Another clue to look for is the presence of a bursa copulatrix, but in very small skins this can be difficult to determine and I would never determine a tarantula’s sex on this alone.
The general shape of the upper alcove can also offer clues to what sex it is in the way of its shape and general form. In females the upper alcove tends to appear wider and deeper than that of males, but again this is not a very stable way to determine the sex on its own, but added to other keys in the puzzle I have found it can prove useful for smaller moults.
It’s also interesting to note that in the case of males it is often possible to make out a dense hair patch above the male gonopore when the moult is lighted up from below, which seems to tie in with Mark R. Hart’s and Rick C. West’s method of sexing living tarantula spiders by the presence of fusilla, which are in laymen’s terms small spinnerets that are present in male tarantulas, and used in the construction of sperm webs.
Exception to the rule!
It is the general opinion that the presence of a spermatheca indicates whether or not you have a female tarantula or not, but there are as yet two species of tarantula where the female lacks these.
The two species in question are Encyocratella olivacea Strand, 1907 (Gallon, 2003, 2005) and Sickius longibulbi Soares & Camargo, 1948 (Bertani & da Silva, 2002; Kunz, 2003-4).
So how now are you going to tell if you have a female or male when you are missing the main sexing key? The answer is in fact quite simple, as even though the spermatheca is missing the females still shed a uterus externus (fig 5) as with all species. It is for this reason and the fact that male epigastric organs can be mistaken at times for spermatheca, that I think the main key for determining a tarantula’s sex is the presence of a uterus externus.
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/Encyocratellaolivaceauterusexternus.jpg
Fig 5
Tools for the job
For larger moults it is more often than not possible to sex them with the naked eye as the spermatheca and uterus externus will be quite prominent and well defined in most cases, but as the moults get smaller the more enlargement of the epigiynum area is needed. By far the cheapest enlargement tool would be a magnifying or spy glass. You can get these in a variety of magnifying strengths and to a point they can be very useful. The main problems with these come when you are trying to unravel the moulted skins while holding the spy glass at the same time.
The most valuable piece of equipment to invest in is a binocular stereomicroscope with a magnification range of x10 to a max of about x100. Anything above x100 is too much as the working space under the lens then becomes too small. A big advantage with these is that you have your hands free to unravel and manipulate the moult so as you can see it clearly.
Many of these types of scopes also come with one or more light sources that can be adjustable, this is a real god send when in some species the uterus externus and spermatheca can appear transparent, so a good light can pick up the shadow and highlight them.
Off course these microscopes do not always come cheap and it often worth while to shop around at second hand stores or different internet shopping sites etc such as Ebay.
I would advise that if you are able to try out the microscope before you buy its best to do so.
For unraveling moults I soak them in a solution of warm water and washing up liquid (approximately 1 part washing up liquid to 100 parts water) until the moult is hydrated enough to be pliable enough to spread out. To spread them out I use a pair of mounted needles and a small artist’s paint brush, but at the end of the day it’s what you find what is best for you to achieve this sometimes very fiddly task.
Other things I use are Petri dishes or glass plates to lay the skins out on and a fine pair of tweezers that can also aid in opening the moult.
What is very important especially in smaller moults, is to lay the moult a flat as possible in the epigiynum area in able to see it clearly. It is also suggested that you take your time and don’t rush when unraveling the moult.
Why?
So what is the point of sexing your immature spiders? Well the main reason for me is so that I plan out mating loans or if I have both immature females and males of the same species, I can attempt to slow down the male’s growth rate or attempt to speed up the female’s growth rate with a view of a future mating. It’s also interesting to note the development of a female’s spermatheca, which alone can also tell you if they are mature enough to attempt a mating by how much they have developed. This can also give you some clues as to the spiders approximate ruff age.
For more information about theraphosid spider sexing you might like to enlist on the sexing course that is ran by the British Tarantula Society study group. Not only is it useful, but also very interesting and covers a wide aspect that not only includes sexing but how spiders moult among other things. Details of this course can be found on the British Tarantula Society web site. www.thebts.co.uk
References
Bertani, R. & da Silva Junior, P. I. 2002. The first mygalomorph spider without spermathecae: Sickius longibulbi, with a revalidation of Sickius (Araneae, Theraphosidae, Ischnocolinae). The Journal of Arachnology, 30: 519-526.
Gallon, R. C. 2003. A new African arboreal genus and species of theraphosid spider (Araneae, Theraphosidae, Stromatopelminae) which lacks spermathecae. Bulletin of the British Arachnological Society, 12 (9): 405-411.
Gallon, R. C. 2005. Encyocratella olivacea Strand, 1907, a senior synonym of Xenodendrophila gabrieli Gallon, 2003 (Araneae: Theraphosidae: Stromatopelminae) with a description of the male. Zootaxa, 1003: 45-56.
Hancock, K. & Hancock, J. 1989. Sex determination of immature theraphosid spiders from their cast skins. Manu.
Hart, M. R. The proper technique for sexing living theraphosid spiders.
http://www.birdspiders.com/faq_sex.html
Kunz, K. 2003-4. Keine Regel ohne Ausnahme: Sickius longibulbi, eine Vogelspinne mit ungewöhnlicher Genitalmorphologie. Draco, 4 (16): 89.
By Chris Sainsbury
*This article is reprinted with the permission of Chris Sainsbury (Tescos) and The British Tarantula Society (thebts.co.uk). This article was originally printed in the BTS Journal, Issue: November 2006, Vol. 22 No. 1. Just one of many reasons to join (http://thebts.co.uk/faq.htm) this great organization.
Introduction
I’m writing this article mainly due to the number of posts on internet web sites where the poster is asking about what sex his or her tarantula is based on a photo of its shed exuvia. Although many of the replies to such posts are often correct, they often don’t go into the reasons why they say it is a female or a male except by saying that they can or can not see a flap. My aim here then is to try and explain some of the key parts of the male and female exuvia when it comes to sexing them correctly and to try and provide some useful hints and tips to help you in the process of sexing your own tarantulas.
What and where?
Theraphosid spiders can normally be accurately sexed by a shed moult from the 5th-6th moult onwards. I have found some species can be sexed one or two moults before or after this stage but it is often an educated guess when sexing specimens before the 5th moult.
The main `trick´ to sexing theraphosids, is having the knowledge of where to look and what exactly you are looking for on a moult.
This might seem quite obvious, but it is surprising what mistakes can be made by not understanding some of the structures that you might see when looking at an exuvia under a microscope or even with the naked eye.
Figures 1 & 2 (below) show the relevant key features of a female and male moult respectively. These labeled features are listed below with their functions.
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/femaleepigynumfig1copy.jpg
Fig 1
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/Maleepigynumfig.jpg
Fig 2
Arthordial membrane; shed muscle attachments that mark the limits of the epigiynum area on the left and right.
Slit sensillum; small button hole like stress detectors that can be found in the upper alcove.
Upper alcove; forms the nose of a females epigiynum area and is where you will find the females spermatheca.
Spermatheca; found only in female theraphosids, this is the place where a males sperm is stored after mating. It develops from a paired structure but can form into pared or fused organs and is located in the lower half of the upper alcove behind the uterus externus that it extends off from.
Uterus externus; a thin often transparent pocket like membrane found only in females, the opening of which is called the gonoslit. It is the only part of the uterus that is shed during a moult and joins to the uterus internus and leads to the oviduct and ovaries, but these of course are retained by the tarantula during a moult..
Gonoslit; this is the opening to the females sexual organs that can be found in the epigastric furrow.
Epigastric furrow; this is located on the underside of the abdomen between the two anterior book lungs. It is a fold in the skin that’s leads to the gonoslit or in the male’s case, the gonopore.
Bursa copulatrix; often called the lower alcove; this is where it is said eggs and sperm mix during egg laying.
Antererior book lungs; these are the two front most feathery type lungs nearest the cephalothorax that the spider uses to breath.
Gonopore; this is the opening to the males sexual organs. In a moult it appears small and buttonhole like with thick lips.
Male epigastric organs; found only in males these organs produce a liquid that mixes with the sperm (recently found out they may also/or be slilk glands use in sperm web production). They can be mistaken for spermatheca especially in smaller moults if you’re unsure what they look like.
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/Lasiodoraparaybanaspermathecafig3co.jpg
Fig 3
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/Brachypelmaaugustummaleorgansfig4co.jpg
Fig 4
In figures 3 and 4 you can see that male epigastric organs differ from a spermatheca in the way of looks by having a base that is much narrower than the body or head of the structure. In the majority of cases they resemble small mushrooms or child like drawings of trees but in small moults they can very much resemble a developing paired spermatheca which can cause some confusion.
These in smaller moults tend to be situated quite close to and to either side of the gonopore but as the moults get bigger I have found that their position tends to move outwards but still based at the same base line as the gonopore.
Spermatheca on the other hand, have a base that is typically as wide as or wider than the body or head. In cases like this where you may be unsure if it’s one or the other there are other certain features to look for. The big clue then would be to see if it has a uterus externus and to study the size of the gonopore. If a uterus externus is not present then you will know you have a male on your hands, also the small gonopore will confirm this if it is very small.
Another clue to look for is the presence of a bursa copulatrix, but in very small skins this can be difficult to determine and I would never determine a tarantula’s sex on this alone.
The general shape of the upper alcove can also offer clues to what sex it is in the way of its shape and general form. In females the upper alcove tends to appear wider and deeper than that of males, but again this is not a very stable way to determine the sex on its own, but added to other keys in the puzzle I have found it can prove useful for smaller moults.
It’s also interesting to note that in the case of males it is often possible to make out a dense hair patch above the male gonopore when the moult is lighted up from below, which seems to tie in with Mark R. Hart’s and Rick C. West’s method of sexing living tarantula spiders by the presence of fusilla, which are in laymen’s terms small spinnerets that are present in male tarantulas, and used in the construction of sperm webs.
Exception to the rule!
It is the general opinion that the presence of a spermatheca indicates whether or not you have a female tarantula or not, but there are as yet two species of tarantula where the female lacks these.
The two species in question are Encyocratella olivacea Strand, 1907 (Gallon, 2003, 2005) and Sickius longibulbi Soares & Camargo, 1948 (Bertani & da Silva, 2002; Kunz, 2003-4).
So how now are you going to tell if you have a female or male when you are missing the main sexing key? The answer is in fact quite simple, as even though the spermatheca is missing the females still shed a uterus externus (fig 5) as with all species. It is for this reason and the fact that male epigastric organs can be mistaken at times for spermatheca, that I think the main key for determining a tarantula’s sex is the presence of a uterus externus.
http://i20.photobucket.com/albums/b219/Tescos444/Other%20stuff/Encyocratellaolivaceauterusexternus.jpg
Fig 5
Tools for the job
For larger moults it is more often than not possible to sex them with the naked eye as the spermatheca and uterus externus will be quite prominent and well defined in most cases, but as the moults get smaller the more enlargement of the epigiynum area is needed. By far the cheapest enlargement tool would be a magnifying or spy glass. You can get these in a variety of magnifying strengths and to a point they can be very useful. The main problems with these come when you are trying to unravel the moulted skins while holding the spy glass at the same time.
The most valuable piece of equipment to invest in is a binocular stereomicroscope with a magnification range of x10 to a max of about x100. Anything above x100 is too much as the working space under the lens then becomes too small. A big advantage with these is that you have your hands free to unravel and manipulate the moult so as you can see it clearly.
Many of these types of scopes also come with one or more light sources that can be adjustable, this is a real god send when in some species the uterus externus and spermatheca can appear transparent, so a good light can pick up the shadow and highlight them.
Off course these microscopes do not always come cheap and it often worth while to shop around at second hand stores or different internet shopping sites etc such as Ebay.
I would advise that if you are able to try out the microscope before you buy its best to do so.
For unraveling moults I soak them in a solution of warm water and washing up liquid (approximately 1 part washing up liquid to 100 parts water) until the moult is hydrated enough to be pliable enough to spread out. To spread them out I use a pair of mounted needles and a small artist’s paint brush, but at the end of the day it’s what you find what is best for you to achieve this sometimes very fiddly task.
Other things I use are Petri dishes or glass plates to lay the skins out on and a fine pair of tweezers that can also aid in opening the moult.
What is very important especially in smaller moults, is to lay the moult a flat as possible in the epigiynum area in able to see it clearly. It is also suggested that you take your time and don’t rush when unraveling the moult.
Why?
So what is the point of sexing your immature spiders? Well the main reason for me is so that I plan out mating loans or if I have both immature females and males of the same species, I can attempt to slow down the male’s growth rate or attempt to speed up the female’s growth rate with a view of a future mating. It’s also interesting to note the development of a female’s spermatheca, which alone can also tell you if they are mature enough to attempt a mating by how much they have developed. This can also give you some clues as to the spiders approximate ruff age.
For more information about theraphosid spider sexing you might like to enlist on the sexing course that is ran by the British Tarantula Society study group. Not only is it useful, but also very interesting and covers a wide aspect that not only includes sexing but how spiders moult among other things. Details of this course can be found on the British Tarantula Society web site. www.thebts.co.uk
References
Bertani, R. & da Silva Junior, P. I. 2002. The first mygalomorph spider without spermathecae: Sickius longibulbi, with a revalidation of Sickius (Araneae, Theraphosidae, Ischnocolinae). The Journal of Arachnology, 30: 519-526.
Gallon, R. C. 2003. A new African arboreal genus and species of theraphosid spider (Araneae, Theraphosidae, Stromatopelminae) which lacks spermathecae. Bulletin of the British Arachnological Society, 12 (9): 405-411.
Gallon, R. C. 2005. Encyocratella olivacea Strand, 1907, a senior synonym of Xenodendrophila gabrieli Gallon, 2003 (Araneae: Theraphosidae: Stromatopelminae) with a description of the male. Zootaxa, 1003: 45-56.
Hancock, K. & Hancock, J. 1989. Sex determination of immature theraphosid spiders from their cast skins. Manu.
Hart, M. R. The proper technique for sexing living theraphosid spiders.
http://www.birdspiders.com/faq_sex.html
Kunz, K. 2003-4. Keine Regel ohne Ausnahme: Sickius longibulbi, eine Vogelspinne mit ungewöhnlicher Genitalmorphologie. Draco, 4 (16): 89.