I’ve just spent the last hour (most of it, anyway), watching a spider weave a web. If you haven’t watched a spider spin a web, I highly recommend it whenever you have the opportunity.
I was walking home this quiet evening, when I happened upon a rather large spider. By ‘large’, I mean a spider with the abdomen about the size of a piece of Skittles or an M&M. Its legs could probably span the width of two quarters side-by-side. Anyway, I was walking by, and it had just put down a few basic support threads spanning a bush and a tree about two feet away. This was the first time, as far as I could remember, that I had seen a spider actually weaving a web. I thought to myself, “Self, you’ve never seen a web woven before, and this big spider is about to weave one right before your eyes. Why don’t you stop and have a look– you’ve got nothing particularly urgent to do tonight.” So I did.
Watching a spider weave a web is one of the more fascinating things you’ll ever see. As you watch this feat of biology, physics, and, well, nature, you will no doubt observe things that are practically hidden from you when you see the finished product. Here’s what I noticed.
Scaffolding: Though I didn’t see the very beginning of the web, I came early enough to see the spider attach most of its main support threads between the tree trunk, its branch, and the nearby shrub. What was interesting was that a lot of structure is put in place before the center of the web was chosen. This support framing consisted solely of long segments, sometimes bolstered by double or triple threading. When it was done, it began the next stage by marking the center.
Centering: The spider marked the center by emitting a few large globs of web-material. I don’t know if it came out of its spinnerets or if it puked them out, but it sure looked like it puked. One instant, it was attaching another support line somewhere in the web, and the next instant, there was a few army-ant-sized globs hanging on the web. I would later discover that this was the new center of the web. Now that the center was chosen, it could now add radial segments.
Radials: The spider deposited its first radials rather sparsely, apparently to lay out some structural support. Only after there was roughly even support all around did it begin filling in. After the first set of radials, it would fill in the gaps with about 12 degree spacing– I counted about 30 radial threads from the center at the end. Once these radials were done, it never laid down any more of them. It proceeded to the spiraling.
First spiral thread set: The spider proceeded to add spiral segments around its center, easily referenced by the army-ant-sized globs. Ring spacing began around 2mm, and would grow gradually, until they were about 3cm apart, about 10 inches or so from the center. Once they got too far apart, the spider stopped, and began filling in the outside.
Support arcs: I suppose there’s a technical term for what it built next, but it laid out arcs at the top and bottom of the outer edge of the web, several inches from the boundaries of the spiral it had just made. The top and bottom each got three or four arcs, spaced about 1cm apart, spanning several radials.
Outside spiral fill: After these supports were put in, the spider began filling in the web in a spiral fashion, beginning with the outside arcs. Spacing was about 7-10mm between rings. This is the final stage (before I began typing this) of the web construction.
Resting: Every now and then, the spider seemed to pause for a several seconds, apparently to rest.
Attaching threads: The spider paused for about half a second to make attachments after each segment. The long, framing threads took a lot longer to attach– perhaps three or four seconds. I now understand why spiders have eight legs. When spinning threads, the spider uses two rear legs from one side to guide and push the thread to the attachment point. Why two? It hands thread from one to the other. And with two legs on a side not supporting weight or providing stability, it assuredly needs another two on that side. It’s attaching a really thin thread coming out of its butt and attaching it to a precise point on another really thin thread, so a lot of stability is required. I never once saw it slip or stumble.
Thread spinning observations: Usually the spider added threads by releasing silk while crawling along an existing thread. It was interesting to watch when it didn’t. In those cases, it would let itself drop slowly, releasing its silk, until it landed on the horizontal segment it somehow knew was there.
Gravity: After finishing, the web’s spiral rings looked really quite evenly spaced. The slightly wider spacing at the top hints at a different story during construction. I was surprised to find that after beginning what I called ‘support arcs’, the additional weight ruined the nice inner spiral, which looked increasingly ruined as more spirals were filled in from the outside-in. Not to worry– the spider re-tightened the innermost spiral rings afterwards.
Final dimensions: The spiral web portion was roughly three feet in diameter. Yes, that means that if you walk into it, it will wrap around your head completely with room to spare. This spider should get some mighty fine eatin’ tonight.
Anyway… you should really have a look if you’ve never seen a spider spin a web right in front of you. A book, DVD, wikipedia entry, or youtube video will just not cut it. It’s a different experience when you can walk around it, put your face as close as you dare, squint to see its impossibly thin threads in the light, and watch the web undulate as the occasional breeze (or breath) blows by (you’ll notice that its rigidity increases with support threads and decreases with sticky threads that catch the wind).
Epilogue: Actually, the spider’s completely finished now. It’s resting in the very center of the spiral, and the globs of stuff that marked the center are now completely gone. Overall ring spacing is about 1cm near the top, and 3-4mm at the center and sides, and maybe 3mm at the bottom. Verily, I marvel.