Handicapping a genuine fight is not always as easy as it seems. As in other endeavors, much of the “everybody knows” knowledge ain’t necessarily so. Consider this case study from the Scientific Research Centre of the Slovenian Academy of Sciences and Arts:
We recently showed that Nephilengys malabarensis eunuchs, i.e. sterile spider males that lost their genitals during copulation, become more aggressive during male–male contests. Here, we add crucial comparative data by exploring eunuch fighting behaviour in Nephilengys livida from Madagascar, specifically by testing the ‘better fighter hypotheses’ in a laboratory setting. Similar to N. malabarensis, N. livida copulations resulted in total male castration with the severed palp plugging the female genitals in 70.83% cases, which mostly (63.63%) prevented subsequent copulations. Unexpectedly, however, N. livida eunuchs exhibited lower aggressiveness than virgin males.
(Thanks to investigator Tom Gill for bringing this to our attention.)