One of the hallmarks of 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 is splendid for revealing many wonders of the natural world normally concealed when water droplets are not present in the air. Last week while driving through the neighborhood, I was amazed by the profusion of spider webs decorating lawns and shrubbery. One smallish boxwood down the street was festooned with more than two dozen webs. The webs were not the typical vertical orbs of concentric circles supported by radial strands. Rather, these webs consisted of horizontal 8 by 10 inch sheets, each bearing a small, remarkably round funnel at one end.
The proprietors of these webs, handsome dappled brown and tan spiders, often perched near the mouth of the funnel. My attempts to photograph these beauties were regularly thwarted by the agile spiders disappearing 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 an Australian funnel web spider is potentially deadly to humans whereas the bite of Agelenopsis pennsylvanica, the Pennsylvania Grass Spider, is deadly only to small insects that are its prey. It is hard to image how a human could be bitten by these shy spiders.
Despite the ability of the web to capture droplets of fog, 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 black and yellow garden spider we met in a previous episode. Instead of trapping prey, funnel weaving spiders rely on a lightning fast attack and fang-strike to immobilize hapless prey that blunder onto their web.
Like many of their kin, the female Pennsylvania Grass Spider engages in sexual cannibalism. The she-spider often eats her mate. Why does she do this? Perhaps she is grumpy or the suitor did not 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. On foggy autumn mornings enjoy the handiwork of funnel weaving spiders and 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. 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.