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
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