Last week, my dispersal-limited self was lucky enough to hitch a ride with Catherine Scott, Sean McCann, Gwylim Blackburn, and Samantha Vibert, to hunt some spiders along Iona Beach. You can read Sean’s blog post (with much, much better photos than I took) summarizing our short evening field trip in rather gloomy, chilly conditions not conducive to salticid-wrangling, but I wanted to relay a particular tidbit that I learned from that trip.
As we explored the habitat above, Catherine and Samantha uncovered not one, but two Phidippus johnsoni residing together in what appeared to be a single little silken retreat on the underside of a log. I collected both–a male and then a female (pictured below, respectively)–harboring in mind Sean’s suggestion to film a mating trial.
Five days later, I returned to the lab intending to attempt this trial, when I noticed that the female had molted, suggesting she was a sub-adult when we collected her. This lead me to hypothesize that the male had been guarding a soon-to-be mature and relatively receptive (as virgin female spiders tend to be) mate. Hastily, I cobbled together a crude “mating arena” resulting in the following video of unremarkable quality:
After mating began, I angled for a better view of the male’s expanded pedipalp, which was pumping away to deliver sperm:
Afterwards, I took to the internet to read up on the Phidippus mating game. Much has been written about Phidippus mating strategies, including those of P. johnsoni, and males’ guarding sub-adult females is well-documented. Apparently the single silken retreat we discovered at Iona Beach was in fact a two-story townhouse of sorts. In preparation for her final molt, the female built a retreat. The male, upon encountering her, likely courted her by tugging at her retreat, and subsequently built his own abode on top of hers. Interesting that courtship can take place before the female has even matured! Of course, placing our subjects together in a vial elicited a different, more visual mode of courtship, as you can observe in the first video.
A male of P. johnsoni‘s eastern North America lookalike, Phidippus clarus, will go as far as to use chemical clues from the female’s silk to infer how soon she will molt into maturity, and will preferentially search for larger females whose final molts are more imminent*. As David Hill relays in his notes on P. clarus, “Snetsinger described how male P. clarus located a female, built a nest on top of the female’s nest, guarded that female from other males, and mated by extending its pedipalps through layers of silk to reach the female, sometimes mating multiple times.”
So there you have it. Even the shortest field trips in rather unfavorable weather can yield new natural history lessons.
* Hoefler, Chad D. 2007. Male mate choice and size-assortative pairing in a jumping spider, Phidippus clarus. Animal Behaviour 73:943-954.