Web design: a masterclass

Helplessly hoping a striped harlequin would pass through the jungle near us, remembering gasping at such glimpses of tigers in the past, I glanced up to the interesting sight of the lady lingering over a hapless fly stuck in the web. By the time I sighted at her and adjusted the exposure against the bright sky she had nearly finished loosely wrapping it in silk.

I’d seen these giant wood spiders (Nephila pilipes) spin their webs across gaps between trees throughout this jungle. In some places, many of them clustered together, making interesting villages of webs. I hadn’t noticed any spinners when I’d come earlier, in the hottest months of the year. They abandon the webs and hide in trees and grass then. Now, seeing their webs, I was glad we had made this trip to Tadoba, even though it was precisely the season when we were least likely to see tigers. This particular web presented an interesting challenge. It was nearly edge on, and the strong backlight was a challenge, but I could see many males clustering around the female. I had to try photographing it.

But first a closeup. The female had a head and torso which was perhaps five centimeters long, and the legs were a little longer. I would estimate the size to be anywhere between fifteen and twenty centimeters. The males, one of which you can see in the photo above, could have been fifty times smaller. They seem to be opportunistic. Several of them hang about in a female’s web, seeking opportunities to mate or feed off her larder (see a photo below). The female does not mind even when they pass fairly close.

I looked carefully for eggs: masses of which are usually bound into a silk purse and tucked safely into the web. None were visible. I found later that this species actually stashes the purse in holes in the ground; bank vaults, if you please. The males seemed to crawl over the web quite fearlessly. The females of the species do not cannibalize the males. These are two major differences between N. pilipes and their nearest relatives. Reconstruction of the family tree of related spiders using genetic methods gives a result consistent with these differences. Genetically too, N. pilipes seems to stand apart from its closest family.

But let’s get on to web design. As you saw in the previous photos, the web is vertical. I’d seen that it wasn’t particularly symmetric, nor did there seem to be a neat spiral structure to the web. Also, very often the female hung off-center, significantly high up in the web. A study found that the heavier the individual, the more asymmetric is the web. The reason the spider waits above the center is that running down is faster than running up. There are other interesting aspects of the web design. N. pilipes seems to tailor the chemistry, and thereby the elasticity and strength of the web depending on the expected size of the prey. The giant dragonfly that you see in the photo above, with males feeding on it, could be the largest prey species that the spider finds. Going by that I would think that these webs are worth studying is more detail. Great design involves attention to many details.