Eunuch or “U-neek” Eeek! Another Spider Sex Story!”


Yesterday I was literally in bed most of the day recovering from a precautionary step to prevent severe illness.   I felt like I had been in a bad auto accident, but that’s got to be better than actually having and/or dying from a virus, right?   Well, I used the time to read.  Mostly I read spider behavior stuff.  Believe me, some of these things are pretty interesting!  Spider sex for instance.  Who knew! I found this somewhat sensational spider story. This spider doesn’t live in the San Juans, but it’s so weird, I just have to share!  

DID YOU KNOW there is such thing as a Eunuch spider? (Tidarren sisyphoides), one of the Theridiidae or Tangle Web Spiders, AMPUTATES one of its own pedipalps (the male sex organs).  The species name (Tidarren sisyphoides) is a combination translation from Gosiute-Greek meaning ‘small male’.  Male spiders of this species are very tiny (1mm) in comparison to females ( only 1% the size of the female).  

According to R.J. Adams (2014) and Ramos et al (2004), Tidarren sisyphoides male spiders are born with, and develop two palps, just like other spiders, but at the penulitimate (next to last) molt (shedding of the exoskeleton as part of growth/development), the male spider amputates one of these palps ON PURPOSE!  

The amputation process isn’t done by chewing or anything of that sort.  The tiny spider wraps it in a silk scaffold, then dismembers the palp by twisting or moving around in circles until it breaks off.  The remaining palp is quite large in proportion to the 1mm sized body of this tiny spider, making up 10% of the total body mass. 

Why would the spider amputate one of its palps?  Well, turns out that males with one palp can move around and chase females much faster with only one palp.  It is supposed to give these guys an evolutionary reproductive advantage.  Males only mate once, so the reproductive drive is stronger than the drive to preserve one’s palp! Once he’s inserted that single palp, he will die within minutes,  still attached to the female. Hmmm, getting laid might not be so lucky depending on how you look at it.

After mating, the female will extricate the palp from her epigynum (the female reproductive receptacle).   While some other species of spiders are known to eat the male after mating, this species does not. She will merely discard the body.   

Interesed in reading more?  Check out these links, and read my blog about spider sex too! 

Adams, R. J., & Manolis, T. D. (2014). Field Guide to the Spiders of California and the Pacific Coast States (1st ed.). University of California Press. http://www.jstor.org/stable/10.1525/j.ctt5hjhpb

Kuntner, M., Agnarsson, I. and Li, D. (2015), The eunuch phenomenon: adaptive evolution of genital emasculation in sexually dimorphic spiders. Biol Rev, 90: 279-296. https://doi.org/10.1111/brv.12109

Ramos,M.,  Irschick, D. J., and Christenson, T.E.  2004. Overcoming an evolutionary conflict: Removal of a reproductive organ greatly increases locomotor performance. Proceedings of the National Academy of Sciences  101 (14) 4883-4887; DOI: 10.1073/pnas.0400324101 https://www.pnas.org/content/101/14/4883

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