I reached down to collect some calendula seeds in the Herb Demonstration Garden on Monday, and came up close and personal with this beautiful spider.
Laurie C. was kind enough (and brave enough – given her confessed arachnophobia) to come in and get pictures.
The web is right in the middle of the lavender patch at the center of the Herb Garden.
We’ve narrowed the ID down to Argiope aurantia (Yellow Garden Spider), or Argiope trifasciata (Banded Garden Spider) and asked Alex to confirm.
Argiopes, like other orb-web spiders, weave an additional pattern of white silk in their webs (visible in the center of the web in the first picture), called stabilimenta. Scientists are unsure of the purpose of the stabilimenta, speculating that they provide an additional attractant for prey, that they can be used to scare off predators, or that they provide a visible means for birds and mammals to notice the web and leave it undisturbed. One of the common names for aurantia, is writing spider, for the resemblance of the stabilimenta to writing. Charlotte must have belonged to this family.
The Cooperative Extension Fact Sheet, Commonly Encountered Pennsylvania Spiders, is an excellent resource to hand out to the public when you're covering the help desk and you're asked about a spider specimen.
Check out this battle between an aurentia garden spider and a huge cicada-killer wasp.
UPDATE: Alex says A. trifasciata and sends this picture of A. aurantia that he took in Delaware County, PA.
UPDATE II: Alex went back to the Herb Garden and took these pictures: