A small and dangerous world

We spent a couple of nights last week in an extremely wet part of the Sahyadris. I’d expected the room to be full of mosquitos. It wasn’t. I discovered why only when I turned my macro lens on the lovely brick wall that the architect had designed. It was meant to be a substrate on which moss would grow. Indeed it does. But my camera caught more than moss, as you can see. The canyons between the bricks were walls of silk.

Mosquitos, and other insects were decimated by the microscopic predators which live in the environment that we have built for them. My macro lens barely caught a glimpse of the spiders; they are less than a millimeter across (you can barely see it in the photo above). I won’t find it listed in a field guide. If I want to identify it I will have to catch an expert. I wonder where they used to live before humans began to build an ecology specially for them. We worry so much about feral dogs and the loss of cheetahs. We have no idea what havoc we play on the ecology at these sub-millimeter scales.

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.

Saturday’s spinner

There was only one tree on the sloping meadow in Khandala where I went trigger happy with my camera. The Family sat under it during the shower while I stood in the rain taking photos of raindrops on roses or anything else in sight. When I joined her in the shelter, I noticed a spider web right above us: a perfect spiral dewed with raindrops. Just the kind that my nieces loved during their goth phases.

A spider waited at the center of the web, perfectly still. Its eight legs were paired into feelers touching four quadrants of the web. I wonder why they are paired up. Does it give the legs better distance resolution? Like the way our paired eyes give us a sense of depth?

Round the web

I stop at this spot in the garden once a day. I’m sure to see some butterflies here at any time. Yesterday I saw this strange spider web. A spider web has radial threads which aren’t sticky; these are the first threads that the spider lays down to make sure that the web will be stable. Once these anchors are in place, it moves crosswise along them laying down the sticky spiral thread. If you look carefully, you can see the fine lines of this spider’s radial and spiral architecture in the featured photo. But the spider was doing something weird here. While it moved spirally along the web, it seemed to lay down a much thicker spiral.

I haven’t seen anything like this before. I read later that when a spider wishes to move, sometimes she eats up the old web. Could she have been doing that? Maybe she lays down something to soften the thread before eating it? Videos on YouTube (a great reference site for the amateur naturalist) show that the dismantling of a web is very straightforward; the spider doesn’t have to season the silk before eating it. Nor was this the process of wrapping prey in silk. Could it be an invader trying to attack the original inhabitant? As I watched, I saw only one thing moving. I cursed myself for not carrying a magnifying lens with me. I went back again today to look. The web had disappeared. Maybe it was an invasion that I had seen.