April, 2005

Filmy Dome Spider

While we try to keep our newsletter as inoffensive as possible, we're pushing the limit of family viewing here showing a pair of spiders, yes, engaged in the act of reproduction. These are filmy dome spiders (Neriene radiata), and they are one of the most numerous of our arachnid species. Filmy dome spiders are members of the sheetweb family, and their web is mostly a jumble of silk strands, with a barely visible "dome" under which the spiders often rest. The spiders are about 3/8 of an inch long, with the female being just slightly larger than the male. Unlike some spider species, in which the male is so tiny that the female does not even notice him, or others where the size of the genders is almost equal but the female has a penchant for eating the male rather than treating him as a mate, these spiders are experts at domestic harmony. Many of the webs in our yard have both a female and male living together. The female in this photo is on the bottom (an almost universal position when the spiders are getting serious), but since they are both hanging upside-down, one could argue that the female is actually on the top in their own topsy-turvy world. In any case, the male is thinner, has a reddish brown head, and has large black appendages sticking out of his face. Mating seems to take a long time and I've seen them engage and retreat several times. The object of spider sex is for the male to place a pair of sperm sacs into the female. He does this with specialized appendages near his mouth (those large black things) called pedipalps. Females also have pedipalps, but they are more like tiny legs, with nothing unusual about the tips. The pedipalps of the male often take on strange shapes that will fit into the appropriate female organ like a key in a lock. The male produces the sperm sac (it looks like a tiny bit of amber) and then uses his pedipalps to transfer it to the female. This process does not seem to be easy and so if I find a pair of spiders in this position, I have plenty of time for taking photos.

Upon finding a recent pair mating in our garden while I was clearing out fallen leaves, I tried to keep from disturbing them while they were busy. When they separated a bit later, I figured it was okay to clean up that area, but accidentally messed up part of the web when I touched it. The female spider continued to just hang lazily where she was, but the male took immediate action. He busily worked for the next 15 minutes at rebuilding the web around the female, looking for all intents and purposes like a hired handyman. I'm sure that females of various other animal species would simply love to have a mate that would take care of ALL their needs so efficiently.