Thread: Rare Wolf Spider

For the arachnophiles out there ...

This unusual spider turned up in one of my pitfall traps a couple of days ago. A bilateral gynandromorph, it is male on the right side of its body and female on its left side. The species is Trochosa terricola (Lycosidae).

Palmgren (1979) estimates a 1-in-17,000 frequency for gynandromorphs among spiders: http://www.sekj.org/PDF/anzf16/anzf16-183-185.pdf

What interests me is the fact that this spider is so evenly divided down its middle. I wonder how it developed to end up this way? What caused not just the gynandromorphy, but the male traits to end up on one side and the female traits on the other?

More photos and info on this specimen here: http://bugguide.net/node/view/512530

if people want to pursue with more interest may i suggest arachnofiles.com and venomlist.com

That is so wild, thank you for sharing that. I would love to get that thing into a lab and run some tests. It is so interesting how 50/50 it is, almost perfect, great find. Whats the geographical location of this finding?

Collected just outside Whitecourt, Alberta, about 150 km northwest of Edmonton.

I have zero knowledge on the topic but it does still strike an interest. Can you point out some of the things that define its sex so I'm not sitting here playing spot the difference?

Originally Posted by somfooleishfool

I have zero knowledge on the topic but it does still strike an interest. Can you point out some of the things that define its sex so I'm not sitting here playing spot the difference?

For one the pedipalps are notably different. Pedipalps are the front most pair of "legs", the small ones near the mouth, and they are actually used in arachnid reproduction. The left one has the enlarged bulb of a male while the right one is the slender one of a female.

cool, thank you. I had noticed that but I was wondering if there was anything else. Still fascinating not only the 1/17k odds of getting one of those, but times that by the odds of that 1 in 17k being one of the spiders you caught (I apologise, poor English there).
on another note, after reading this post it got my curiosity peaked as to what spiders look like while they are growing, would anyone know where I could find a photo timeline of a spider growing from infant size to full maturity? I did search but to no avail.

Originally Posted by somfooleishfool

I have zero knowledge on the topic but it does still strike an interest. Can you point out some of the things that define its sex so I'm not sitting here playing spot the difference?

The differences between the left (female) and right (male) palps, as Paleoichneum mentioned, are one obvious feature. The female sex organ, the epigyne, is found on the underside of the abdomen and isn't visible in the above picture. Here is what a normal epigyne looks like for an adult female T. terricola. In the bilateral gynandromorph only half of it is there, on the female side of the midline:



Another feature: both male and female internal sexual organs are often present in these bilateral gynandromorphs, too, male testes and females ovaries, each on their respective sides of the spider.

Normal males and females of this species exhibit sexual dimorphism. Males are generally darker colored and have longer legs than females. Here are pictures of a normal female (top) and a normal male (bottom) I collected last year in which you can see these differences:





These male and female differences are present to some extent on their respective male and female sides in the gynandromorph. Legs I and II on the male (right) side of the gynandromorph, for instance, are longer and some segments are darker or redder than their counterparts on the female side. You can kind of see these differences in a picture I took of the underside of the gynandromorph:



Another difference that's just visible in the photo in the OP: the female chelicera is longer and more robust than the male chelicera, reflecting the normal dimorphism between males and females in these appendages.

There are also some subtle color differences on the abdomen between one side and the other than don't show up as well in the photos.

The spider is still alive, but after I preserve it in alcohol I'll take closeup photos, including some of the half-epigyne, and post them at the original BugGuide page for this specimen.