Tuesday, August 11, 2009
Sheets of Webs and their Weavers
In a messy garden such as mine own, and even in more tidy ones like yours you'll find sheets of spider webs draped across the shrubs. Sometimes these horizontal sheets cover several square feet, and on a dewy morning or after you run your low flow spinner-spitter sprinklers the webs will glisten with the captured droplets of water in them. It's amazing how much water these webs will hold, and amazing just how many webs there are in the garden and how extensive they can become. Here are some of my rudbeckia hirta flowers without the web shown in the top photo.
The spiders responsible for the sheets of webs are Agelenidae, the funnel web spiders. If you examine a web you'll find off to the side or in a low spot a funnel of silk retreating into a quiet recess within the shrubs, or a folded niche inside a flower and sometimes a crevice in some wood or other stuff you've got laying around the yard. This is where the spider hides waiting for prey to become entangled in the large web she's woven. The female spider stays in the web eating and gaining weight, waiting for a wandering male to find and mate with her. She then produces a flat disc-shaped egg sac and will probably die as winter progresses.
These spiders eat whatever insects (and sometimes other spiders) that wander into their grasp and so help to maintain the ecological balance of the garden. The remains of their predations can easily be found in the webs, as well as other random garden detritus that falls onto the horizontal silk surfaces. Here is a fiery skipper that meant to nectar at the rudbeckia flower but ended up giving its life for the cause of more funnel web spiders. A big web traverses several stalks of my bronze fennel, Foeniculum vulgare 'Purpureum' and holds a shed exoskeleton of the fork-tailed bush katydid Scudderia furcata along with fallen flower parts of the fennel itself. The shed exoskeleton of the spider herself is seen suspended as if dancing.
There are 85 known North American species in the funnel-web family Agelenidae so it's hard to say which species my sheet-weavers are. However, I would wager a guess these are in the genus Hololena based on their appearance and that genus is the most commonly found in southern California. Here are some female funnel-web spiders: the one responsible for the massive web entangling the rudbeckia; an attractive one that lives on a dusty miller leaf; and the one living and weaving on the fennel which appears to gravid: swollen with eggs.
Yes, the webs can be messy. Occasionally even I hose off webs which have become especially encrusted with dust, fallen plant parts, etc. I'm not entirely sure this measured cleaning effort is detrimental to these spiders' endeavors. The old webs covered with debris possibly aren't that effective at catching prey and may even have been abandoned by the spiders, except as a familiar hangout, in favor of fresher webs. That said, of course if you're out there fanatically cleaning away webs every day or so the spiders are not going to prosper and will move on to a quieter more natural garden. Giving the spiders a bit of space to dwell in gives me their services of predation as well as another interesting microcosm to study and enjoy.