One delightful meteorological event marking the transition from summer to autumn in the mid-Atlantic region is fog, small water droplets suspended just above the ground as moist air cools. Morning fog reveals the numerically astounding and perhaps somewhat disturbing presence of spiders whose webs usually go unnoticed in the landscape. Last week on one of these misty mornings, my neighbor’s pachysandra bed was festooned with more than a dozen gossamer webs. The webs were not the typical vertical orbs of concentric circle supported by radial strands like those of black and yellow garden spiders, spotted orb weavers, or marbled orb weavers we met in previous episodes. Rather, these webs consisted of horizontal 8 by 12 inch sheets, each bearing a small remarkably round funnel at one end. The proprietor of the web, a handsome dappled brown and tan spider, often perched near the mouth of the funnel.
My attempts to photograph these beauties were regularly thwarted by the agile spiders’ ability to disappear down the funnel in the blink of an eye. Funnel weaving spiders, a.k.a. grass spiders, are often confused by name with their more famous and perfidious relatives the funnel web spiders. The bite of Australian funnel web spider is potentially deadly to humans whereas the bite of Agelenopsis pennsylvanica, the Pennsylvania Grass Spider, is deadly only to their tiny insect prey. It is difficult to image how a human could be bitten by these shy spiders. Despite the ability of the web to capture droplets of fog, the silken strands of funnel weaving spiders cannot snare small insects. They lack the sticky polymer found on the bug-catching strands of spider webs like those of the large orb weavers. Instead of trapping prey, funnel weaving spiders rely on a lightning fast attack and fang-strike to immobilize hapless victims that blunder onto their web.
When threatened by a predator or bug geek, the funnel weaving spider can disappear down its funnel in hole in the blink of an eye.
Like many other arthropods, including the praying mantis and black widow spider, the female Pennsylvania grass spider engages in sexual cannibalism. The she-spider often eats her mate. Why does she do this? Is she grumpy or did her suitor’s performance fail to meet expectations? In a clever study scientists discovered that hungry and particularly aggressive females tended to be cannibals. More importantly, the cannibalistic females produced heavier egg cases and the eggs within each case experienced increased success of hatching. If you are a female Pennsylvania Grass Spider, it pays to eat your mate. So for us humans, enjoy the handiwork of funnel weaving spiders on a foggy autumn morning; but if you are a male funnel weaving spider, think twice about who you date.
Bug of the Week thanks non-cannibalistic Dr. Shrewsbury for photographing and wrangling spiders for this week’s episode and Dr. Shultz for providing the identification. Two excellent references, “Some Commonly Encountered Pennsylvania Spiders” by Steve Jacobs and “Sexual cannibalism is associated with female behavioural type, hunger state and increased hatching success” by Aric Berning and colleagues, were consulted.