Spiderlings sexes

[Sarah Wells]

Hi i was just sitting thinking, in a tarantula egg sac, are there more likely to be more males than females or the other way round, or does it just vary, Ive tried googling but cant find a answer any where

[Peter Roach]

I would hazard a guess that no-one ever has tried to find this out, as to do so every spiderling would have to be kept and raised until they are at a minimum several months old and in some species upto to several years old.
Very few people have the space to keep the contents of an entire egg sack which can be from 100 to several thousand or would even want the responsibity of raising, feeding etc hundreds or thousands of slings just to find out the sex ratio of a tarantulas egg sack (except possibly someone doing a research paper) also as there are approx 800+ (?) species of Tarantulas there may be variations in the sex ratio's among the different species.

[Sarah Wells]

Thanks for replying I guess we will never know. Would be interesting to find out tho

[Peter Lacey]

As a general guide I'd suggest around 70% male to female, but I have no real basis for it.

[Peter Kirk]

This is a fascinating question and I would be intrigued to see the statistics on this, should anyone be in possession of such facts. I was interested by your reply Peter - I have always understood that the ratio is more likely to be the other way round with 70% being female. However, like yourself, I cannot lay my hands on any resource with would either conform or disprove this.

All I would say in my defence, your honour, is that things tend to happen in nature for reasons of survival. It makes sense to me to have fewer males simply because one male can mate with multiple numbers of females. If, say, a male is lucky enough to mate with (on average) four females - not too difficult to imagine within a population of tarantulas - that works out to roughly the right numbers.

What does everyone else reckon - anyone have any information regarding this? Peter - what about data from some of your communal Pokie experiments?

[Peter Lacey]

Ive kept a number of communals, including P. cambridgei and P. murinus but recording the sexes has been difficult. You can't ask "who's moult is this?"
However, having a large amount of pokies together has shown a slide towards males. As an example, out of the 9 rufilata that Peter Kirk saw at one of my gatherings 6 turned out to be male, and the other 3 didnt seem to do well at having the heirachy redefined!

Sticking with pokies, I have found that the maturity of the males varies quite a lot. Ive had MM regalis/striata/rufilata mature at least a year after the first MM from the same sac!

What I can provide an insight to is GBB. I purchased 23 of these from Sven Koppler a few years back, sold a handful off and it resulted in 3 females. I'd suggest the ratio to be 80% male. I currently have about 15 juvenile GBB which I hope to get a better ratio from. And, if I'm really lucky this sac will bring a huge smile to my face!

[Colin D Wilson]

It's been suggested with a moderate amount of scientific proof that some animals (i.e. crocodilians) will adjust their incubatory methods to promote male or female offspring dependent on the existing percentage in the area they inhabit (i.e. lacking males one year (through predation or illness) will lead to more males being born the following season)

Don't know how this could be proven or disproven but could the female incubating the egg sac "adjust" or "pre-determine" the sex of the resulting offspring through incubating varients etc.

Obviously when we incubate sacs ourselves then this would negate this and we wouldn't get naturally occuring data.

I've noticed with the sacs i've had here (that i've kept the majority of the sac) a larger proportion of female to male, these have been both left with the mother and artificially incubated.

theoretically it wouldn't matter in my opinion ....

More males in sac ... would mean a larger spread of males to proporgate the species, there would be a better chance of a female being mated.
More females in sac ... would only mean the males had to mate a few times more with different females (of which there would be more readilly available)

[James Box]

wasn't there something about Lampropelma violaceopes/C sp Singapore Blue having a ratio of 5 to 1 male to female?

it'd be interesting if there was a way to induce more females than males...but sacs are fiddly as they are lol!

[Peter Roach]

[QUOTE=Peter Lacey;5526]

What I can provide an insight to is GBB. I purchased 23 of these from Sven Koppler a few years back, sold a handful off and it resulted in 3 females. I'd suggest the ratio to be 80% male. I currently have about 15 juvenile GBB which I hope to get a better ratio from.

Do you think that GBB's may have such a large percentage of males due to the females tendancy of eating the males before mating ?

[Mike McNeill]

I was directed here after asking this question on the Facebook page.
I too have wondered on the ratios, I also wondered if these ratios vary depending on certain factors. Factors such as temp, humidity, incubation period, the species. Even down to the environment and surround population of Tarantulas and the current amount of males and females present in the area possibly (and how would that affect captive bred), or even the age of the Tarantulas involved in the pairing.
I understand it is a big undertaking to keep the whole contents of an egg sac to a sexing age to determine the ration, plus this i would have thought has to be done over a period of years. Doing the research on just one egg sac surely wouldn't give a true reflection on the average ratio, wouldn't this need to be done over a few egg sacs at least.
But as a community could this not be achieved? If someone was to sell to members of this community, who then report back to the original breeder once they sex their T. A record could then be kept. I know that is still a fairly big undertaking and would take the cooperation of all who buy a sling. But i think it would make it easier to do the research, rather than one person alone trying to keep them all.

[John chambers]

Re: Spiderlings sexes

I was directed here after asking this question on the Facebook page.
I too have wondered on the ratios, I also wondered if these ratios vary depending on certain factors. Factors such as temp, humidity, incubation period, the species. Even down to the environment and surround population of Tarantulas and the current amount of males and females present in the area possibly (and how would that affect captive bred), or even the age of the Tarantulas involved in the pairing.
I understand it is a big undertaking to keep the whole contents of an egg sac to a sexing age to determine the ration, plus this i would have thought has to be done over a period of years. Doing the research on just one egg sac surely wouldn't give a true reflection on the average ratio, wouldn't this need to be done over a few egg sacs at least.
But as a community could this not be achieved? If someone was to sell to members of this community, who then report back to the original breeder once they sex their T. A record could then be kept. I know that is still a fairly big undertaking and would take the cooperation of all who buy a sling. But i think it would make it easier to do the research, rather than one person alone trying to keep them all.

The idea sound's good, But the practice might not work unless there was devoted people to really help.

[John chambers]

Re: Spiderlings sexes

As a general guide I'd suggest around 70% male to female, but I have no real basis for it.

Most of what I get land up male lol..
Wonder if temperatures might play a part ?