Spider Exuvia, Web and Decoration

Description:

Argiope luzona (Walckenaer, 1841). When I first spotted this spider web with its decoration and exuvia, I thought that I had come across a spider in the process of moulting its exoskeleton. This is always a fascinating event to witness. So I took one photo for my "spider census" and then took some additional shots, for the purpose of illustrating the moult. However, I soon realized that the spider was not there. I was not witnessing a moult. I was looking at an exuvia. This immediately raised the questions "Where was the spider?" and "What can I find out about the spider from the remaining evidence?". The exuvia looked "fresh" and complete. The spider web (which was shaded by the upper leaves of the banana plant) does not show well in my pictures, but I could see that there was no damage of any kind. As for the web decoration, it is a perfect example of a "Four-arm Continuous Cruciate Stabilimentum". Judging by the size of the exuvia, this was a very small spider. Males do not make This type of stabilimentum. So, my spider must have been a female. It is also known that small, young female A. luzona spiders make only Two-arm or Four-arm Stabilimenta (when they grow bigger, they produce One-arm, Two-arm. Three, Four and Five-arm stabilimenta). So, we can build up a "picture" of our spider, without actually seeing it. The evidence shows that it was a young female which was just at the point in its life where it was developing from sub-adult to adult. However, the question remains - "Where is it?". I think there are two possibilities. The first is that the spider saw me coming towards it and (if it had recovered enough from its moult) dropped to the ground, like a stone (rapidly feeding out a silk thread to enable it to climb back up when the danger had passed), but I passed my hand from side to side, under the web and felt no life-line. So, that seemed unlikely, but not impossible. Sometimes the line breaks, during the fall, then the spider has a more difficult climb back up to its web when it feels safe to do so. The second possibility (and I think the more likely) is that the spider was snatched by a spider wasp. Normally there would be some "tell-tale damage" to the web, from the spiders struggle, but there would be no struggle put up by a spider which was not yet recovered from its moult. My last photo was taken when I returned to the web in the afternoon, to check if the spider had climbed back up after a possible escape and evasion drop to the ground, but no luck. My conclusion must be that this spider was taken by a wasp.

Habitat:

This A. luzona exuvia was spotted in the rice mill backyard, on the leaf of a Banana Plant (Musa x Paradisiaca L.) known, generally, as “Saging” in the Philippine National language and in our local dialect, “Batag”. Plant information from http://www.stuartxchange.org/Saging.html...............

Notes:

This spider exuvia was included in my monthly census of Argiope luzona in the little banana plantation in the rice mill backyard. Despite having deduced that the spider was dead before I arrived, I included it in the "census" because the evidence shows that it had been there (and alive) until an hour or two before my arrival and it is quite possible that any of the living spiders, in my census, could be dead soon after I took my photos. The entire life of Argiope luzona is precarious and the early part of its life is particularly dangerous. When it squeezes its body out of its moulting exoskeleton, it hangs limply for hours, until its new "skin" stiffens enough to support it properly. During that period, it is quite unable to escape from a predator or fight for its life. The casualty rate during moults must be very high. I mention all of this to explain why a "missing/dead" spider should be included in my cencus and to give me the opportunity to mention that although this spotting shows the same exuvia and stabilimentum as those in the "spider count spotting", the above are all different photos, taken for the purpose of this spotting.