The subtle artistry of Mecynogea lemniscata

As far as I knew, I hadn't seen a Mecynogea lemniscata in years. Then, four days ago, I saw one. I returned the next day to examine the web again. It's so delicate that it's difficult to make out details unless the lighting conditions are just so. After that second examination, I knew there was something odd about the construction of that dome. It looked like a regular grid of tiny squares, rather than the series of irregularly sized trapezoids that characterize an orb web*.

Later that day I found another specimen with an amazing web in excellent lighting, and the shots I got just made me more curious. How the heck is that dome constructed? It can't be a regular grid, because the rows seem to follow a radial arrangement. Moving out from the center, the number of squares in each ring has to increase.

Well, today I found dozens more of the same species, and I finally got some shots with enough detail to answer the question of its construction. I cropped two images and circled the spots where one radial row becomes two, two become three, etc. I don't know anything about knitting, but my wife tells me the spider does the same thing a knitter does.

The pictures above show only a section of the dome, and the dome is only one component of an intricate and varied structure. For the last few days I've been wondering if I could shoot a video that would convey that astonishing complexity. Those new specimens gave me the opportunity to do just that.

I managed to approximate the act of examining a Mecynogea lemniscata web in this video. No one photograph or illustration can convey its intricacy. There must be thousands of strands, and the different sections of the web have wildly different types of construction. To take it in, you have to let your eyes range over it, here stepping back to take in the whole thing, there focusing on a few square millimeters. I played with the focus here to simulate that.

*An orb web is just the traditional Halloween web, with radial spokes and concentric rings.

Mecynogea lemniscata with dome web

Three days ago I was delighted at my first Mecynogea lemniscata sighting in years. The next day I returned, and as I scrutinized the web, I began to comprehend its elaborate structure. The strands of the dome seemed to form a regular grid, rather than the variably-sized trapezoids of an orb web.

Just a few hours later, on the other side of town, I found another specimen of the same species. This one had a much larger web, and had built it in a spot that was ideal for viewing, so you can imagine how thrilled I was.

This was my first good, close look at a Mecynogea lemniscata web. Now that I've had the opportunity to scrutinize its structure, I understand what I didn't before: that it's too intricate for any single photograph or illustration to capture. I looked through all the images for the species on BugGuide, and I found only three shots showing a significant portion of a web: one showing a dome shimmering in the sunlight; one showing the strand of egg sacs hanging over a dome; and one showing a magnificent triple-decker stack of domes. Not one of them even begins to convey the intricacy of the web I saw.

The illustration below comes from Harriet Exline's 1948 research study "Morphology, habits, and systematic position of Allepeira lemniscata (Walckenaer)". It's an excellent diagram, but now that I've gotten a good look at a web up close, I see that it's only a diagram. The density and delicacy of the strands is of another order of magnitude than what the diagram shows, because you couldn't pack all those lines into one diagram.

The web of Mecynogea lemniscata is a wonder of micro-engineering, and in order to grasp the intricacy of its structure, you need to let your eye range over it. I would need expensive video equipment to even approach the experience I had with my nose in that web. In lieu of that, here is a selection of crops from the images I took at the time. Hopefully they will give you a sense of the experience, and encourage you to seek out one of these marvels for yourself.

I added the red dots to make the dome profile more visible.

Note the detail of the dome web to the right of center.

Note the deformation in the grid from the anchor line.

Note the profusion of delicate strands pulling up on the orb web to shape it into a dome.

More detail on the strands pulling up on the orb web to shape it into a dome.

More detail on the strands pulling up on the orb web to shape it into a dome.

Note how the lower anchor lines deform the orb into a smooth curve.

Note how the lower anchor lines deform the orb into a smooth curve.

Note how the lower anchor lines deform the orb into a smooth curve.

Closeup of the dome and its architect.

Closeup of the dome and its architect.

Closeup of the dome and its architect.

Closeup of the dome and its architect.

Closeup of the dome and its architect.

Closeup of the dome and its architect.

Closeup of the grid and an anchor line deforming its shape.

Closeup of the dome and its architect.

Closeup of the dome and its architect.

Closeup of the dome and its architect.

Uloborus glomosus parasitism?

Today I visited the shrub where I first observed U. glomosus a few weeks ago, and noticed that one of the strings of egg sacs had a pale sac with a hole in it. Now that I've examined the picture, I think my impression at the time was correct: it's empty. I didn't see any spiderlings, and besides, odds are that a sac on the end of the string would hatch first. So I suspected a predator—probably a wasp—had made that hole.

A few blocks down the street I chanced upon the scene below. As I approached, the U. glomosus specimen shown in the pictures crawled up the egg sac strand. I didn't know whether that movement was in response to my approach, or to the little wasp, but as you can see, she resumed her resting position, and the wasp kept going about its business. So it appears that the spider wasn't aware of the wasp.

A quick look at a few research papers and at BugGuide tells me that chalcid wasps are known parasites of Uloborus, so it seems likely that we're looking at one, although my cell phone shots make it impossible to determine the species.

Uloborus glomosus carrying a bundle while wrapping prey

Yesterday I was lucky enough to encounter this specimen of U. glomosus as it pounced on an insect that had just gotten stuck in its web. I started snapping pictures, and recorded a video. This is a cropped version of that video. It clearly shows the reason I was so intrigued: the black object that the specimen was somehow carrying as it wrapped its prey. 

These pictures show the object, and the wrapping process, more clearly. After studying them, I came to the conclusion that the black bundle was not somehow slung behind the caphalothorax, as I originally thought. I think she's holding it in her chelicerae and pedipalps.

I took these shots about five minutes later. Note that the new prey, on the far right, is fully wrapped, and the specimen is back in her warren, still holding the black bundle. 

Here's a closeup of a bundle from a previous catch...

...and here's a closeup of the specimen with her bundle. What do you think it is? My best guess is that it's the bundled remains of an ant that she's still digesting.