At what size is abdomen considered a viable gender indicator?

[violentblossom]

I've seen this practice used by several enthusiasts, and was wondering at what size approximately this method is even remotely viable?

I mean, obviously it isn't any fail safe indicator in the way that checking the T's underside is, but I was still wondering. Does size matter at all? Can it be done with slings, or do those all have fat butts?

Also, is species and/or arboreal/terrestrial a variant in this?

 

[Teal]

Abdomen size is a matter of how much you feed a T.. any T can be made fat, theoretically (some Ts won't eat enough to be made fat, etc.)

General abdomen shape, I believe, can differ between male and female... but I wouldn't even begin to try to use it as a way to identify gender.

 

[xhexdx]

Let me make sure I understand the question...

You're asking if the size of the abdomen (not pattern, not furrow, but size only) is viable?

I have never heard of sexing based on the size of the abdomen...I can fatten up a male just like a female and never know the difference.

Just my thoughts though, as always.

--Joe

 

[violentblossom]

Abdomen size is a matter of how much you feed a T.. any T can be made fat, theoretically (some Ts won't eat enough to be made fat, etc.)

General abdomen shape, I believe, can differ between male and female... but I wouldn't even begin to try to use it as a way to identify gender.

Thank you for your reply. In response to Joe also: by size, I meant overall size of the T... sling vs. larger tarantulas.

 

[jayefbe]

If you're going by just the size of the abdomen, then at no point is it a viable gender indicator. Abdomens fluctuate in size depending upon where in the molt cycle they are and how much they have eaten. Mature males do have smaller abdomens than their female counterparts, but at that point there's no need to compare abdomen sizes to determine sex.

 

[xhexdx]

Ok, well, I'm still a little bit confused by the question, but maybe I can still offer my personal methods:

When sexing tarantulas, as always, sexing by molt is the most accurate way. I'll sex the same spider's molt every time it molts, even if I got a clear outcome prior. It's a good way to keep my sexing abilities honed.

Ventral sexing is something I don't pride myself on, but I'll often compare notes with my spiders and then verify with the next molt.

I've never tried to sex a spider based on leg thickness, abdomen size, etc.

But, I suppose, you would have a better shot at ventral sexing a spider with a fat abdomen than you would with a shriveled abdomen.

I hope this makes sense.

--Joe

 

[violentblossom]

I have seen people just look at tarantulas and say, "that looks like a female, see how round the abdomen is?"

That's what I'm referring to. I've seen people look at the overall shape (I guess) of a Ts abdomen and makes guesses based on that alone to what the T's gender is.

I'm wondering if there's a line where this just cannot be done.. do male slings of a given species have a different shaped abdomen from a female sling of the same given species, or is that not obvious enough to determine at a small size?

I hope I don't sound idiotic, but I can't really explain any better.

 

[xhexdx]

Alright.

In my opinion, no, you can't sex a spider based on the size of their abdomen.

Maybe you can use it as an indicator, but even then, just get a ventral shot or wait for a molt. It's all speculation till you get a molt anyway.

If I'm wrong, I'd really like examples. Not because I don't believe you, but because I learn better that way.

 

[Ether Imp]

I have seen people just look at tarantulas and say, "that looks like a female, see how round the abdomen is?"

That's what I'm referring to. I've seen people look at the overall shape (I guess) of a Ts abdomen and makes guesses based on that alone to what the T's gender is.

Problem is, that's all they are doing, is guessing. The only ways you can be sure are:

Accurate ventral/molt sexing
Tibial hooks
Gravidity

I'm wondering if there's a line where this just cannot be done.. do male slings of a given species have a different shaped abdomen from a female sling of the same given species, or is that not obvious enough to determine at a small size?

I hope I don't sound idiotic, but I can't really explain any better.

The line it cannot be done is when you wish to mate your T's and need to know the answer for sure. Guessing is just that.. guessing.


Edit: As Joe says, it can maybe be used as a SMALL and almost insignificant indicator.. I mean, females are MORE LIKELY to be fatter/more roundish, and males are more likely to be smaller/longer/thinner overall.. but it's by no means definitive.

 

[Roski]

I have seen people just look at tarantulas and say, "that looks like a female, see how round the abdomen is?"

That's what I'm referring to. I've seen people look at the overall shape (I guess) of a Ts abdomen and makes guesses based on that alone to what the T's gender is.

I'm wondering if there's a line where this just cannot be done.. do male slings of a given species have a different shaped abdomen from a female sling of the same given species, or is that not obvious enough to determine at a small size?

I hope I don't sound idiotic, but I can't really explain any better.

Actually, I know what you mean. At 2.5" my G. pulchripes molted into a thin, oblong abdomen and it still is, no matter how fat he gets (in stark contrast to the vastly rotund behind he would achieve as a sling). I suspected it was a male at that point. Females of the same species and size that I have seen around the boards have a slightly more round abdomen. I had the molt sexed- it was a male .

It's neat, and interesting to consider, but I would personally never consider it a sexing method- more of a casual observation.

 

[xhexdx]

Funny, I just posted this pic in a sexing thread:

Here he is dorsally:

MM boehmei:

Granted, his abdomen isn't HUGE, but it's still round, not thin.

To me, abdomen doesn't indicate anything.

But there could be species where males are more likely to have a thin abdomen, but I couldn't say.

 

[TalonAWD]

Alright.

In my opinion, no, you can't sex a spider based on the size of their abdomen.

+1 In my experience you cannot tell the gender by looking at the spiders abdomen size, shape, eating patterns, or aggression level.

At around the 3" legspan size it gets easier to sex ventrally. But as stated many times not a guarenteed method.

 

[violentblossom]

@ Roski: Yes! That's exactly what I meant.

Thanks for the replies, guys. I've never depended on this method or anything, but I kinda wondered if T slings had some equivalent of baby fat.

@ Joe: off-topic, but that T's quite handsome. (Not the boehmei, but he's nice, too.. the other. I'm not sure what it is. )

 

[Roski]

Great pics, and I wouldn't know about other species. My observations of my pulchripes are just for my own musings (and apparently also violentblossom's).

Interesting, but not much beyond that.

 

[KoffinKat138]

I used to think by looking at the abdomen in general you could sex them by Females having bigger abdomens,and Male's smaller ones,But i went to a LPS and they had a B.smithi with a Huge abdomen,that you would have thought to have been female because of the size,but once i got a chance to look underneath it.It clearly had a Black dot.

 

[gumby]

@OP personally I have never been good at sexing so I understand the question. I actually think that once a T. hits about 4" and its normal size tops out around 5" that you can use how leggy they get as a better indicator then the abdomen. The only 100% sure way to sex is with a microscope IMO.

 

[Stan Schultz]

... I've seen this practice used by several enthusiasts, ...

... who really don't know what they're doing...

... and was wondering at what size approximately this method is even remotely viable? ...

Never.

If you make random guesses, the laws of probability suggest that you'll be correct about half the time. Your example falls into this realm.

If you examine a shed skin from a tarantula that's fourth or fifth instar or older, and you have even minimal experience, your probability of getting it right jumps into the 85%+ realm. And, your success rate will improve slightly with increasing experience.

For newly emerged babies up to about the fourth or fifth instar, your probability of being correct depends on a lot of variables, but lies somewhere between these two extremes.

How lucky are you at gambling?

 

[Endagr8]

Here he is ventrally:

*dorsally.

@OP personally I have never been good at sexing so I understand the question. I actually think that once a T. hits about 4" and its normal size tops out around 5" that you can use how leggy they get as a better indicator then the abdomen. The only 100% sure way to sex is with a microscope IMO.

IME, microscopes are rarely necessary for molts larger than an inch and a half.

 

[xhexdx]

*dorsally. .

Good catch. Fixed.

 

[Kamikaze]

When I was starting out in our wonderful hobby a couple of years ago, I took a picture of my sub adult Lasiodora klugi and showed it to my friend. Since the camera that I was using did not take good pictures, he based his sexing on the abdomen shape, saying that it could be a female since the abdomen shape was robust. (He also pointed out that the book lungs distance made him certain that it was a female)

After a molt later, it turned out to be male.