This reveal for Sign Challenge #1 is long overdue. Here’s the challenge photo again:
Commenter Daniel Heald correct guessed it was a spider egg sac. Here’s another angle:
When I took the photos, I assumed it was a cocoon. I was curious to see what moth would emerge, so I took it home with me.
After looking through Tracks & Sign of Insects and Other Invertebrates, I realized it was actually an egg sac for a Spinybacked spider (Gasteracantha cancriformis). In fact, I had seen many of those spiders in the area. The egg sac’s yellow silk, dark longitudinal line, and placement on the underside of a leaf all point to this species.
In Spiders of the Carolinas, L. L. Gaddy notes that in over twenty years of fieldwork he’s not seen the egg sac or male of this species. Perhaps I’m just lucky, but I suspect I’m more of a leaf flipper than Gaddy. The egg sacs are placed on the undersides of leaves, which is where I’m always checking for caterpillars.
I was curious to see the spider eggs, so I peeled back a few layers of the silk and found the spiderlings had already hatched. Turns out they stay in the egg sac for weeks before emerging.
I had hoped to see the spiderlings grow, but they all died after a few weeks.
This’ll be the first in a new series of challenges focused on sign. What is “sign”, you might be asking? Generally, it’s something whose presence indicates the presence of something else. Here on this blog, of course, I’m referring to sign in nature. That could be tracks an animal left behind, scat or other droppings, a shed skin, feeding damage, and so on.
So, with that in mind, what is this sign and what critter does it reveal?
I highly recommend Tracks & Sign of Insects and Other Invertebrates. I find that it’s one of my most used references of late. If you already have it, you’ll find the answer to this challenge in it.