The signs of impending winter are upon us. While the heat made one final appearance for the Sports Day long weekend, nights and early mornings have become decidedly chilly. The sun is setting early, and leaves are changing colour.
Recent news has been dominated with the landslides on Izu Oshima island, caused by Typhoon 26, which have resulted in over two-dozen confirmed deaths and nearly a dozen still missing. To make matters worse, Typhoon 27 is following a similar path, and Typhoon 28 is also on the way.
It was on one of those warmer, sunny mornings (autumn is known as the season of clear skies, except when the typhoons come through and dump several hundred millimetres of rain in a few hours) when I noticed how big some of the jorogumo had become, and was spotting their webs in all kinds of places. I saw around half a dozen in the 20+ mm class along the Azuma River, their webs stretched between the cherry branches and the guard rail. Further along I spotted a few more, smaller spiders with webs spanned between electricity poles and roadside hedges.
That was when I spotted a web with stabilimentum (web decoration), a linear zigzag pattern. This web no doubt belonged to a member of the genus Argiope. This was going to be worth examining more closely.
Unfortunately, the spider had positioned herself on the other side of her web, facing the morning traffic. Traffic is not only a genuine life-threatening risk, it is also the curse of arachnidian photography – every vehicle that passes caused the web to sway several centimetres, and out of focus. The low, direct sun also played havoc with exposure, and I had to abandon my attempts, wondering if the spider would still be there after the typhoon…
…which it was.
Thanks to my field guide, I was able to quickly identify the spider as a wasp spider (Argiope bruennichi). This spider has a wide range, and is found right across the Japanese archapeligo, much of the Asian mainland, parts of Africa to northern and central Europe. Unfortunately, I have not been able to find the etymology of its English name. The Japanese name, nagakoganegumo (長黄金蜘蛛), is somewhat easier to deal with; it suggests that it looks like the orb-web spider (Argiope amoena) or koganegumo, but is longer.
Female wasp spiders can grow to 25 mm in length, and this one was about that size. Males are typically about half the size of females, and their markings are not as distinct as the females’. Like other orb-weaver species, males often do not survive mating.
While many other Argiope species spin X-shaped or diagonal stablimenta, wasp spiders tend to spin rings as juveniles and vertical linear patterns as adults.
The adult spider typically waits in the centre of its web, head downwards.
The wasp spider is less agressive than A. amoena, and so are not used in spider-fighting bouts (I hope to get some good photos of amoena next year and write a little about spider fighting). Its venom is not known to be harmful to humans (usual caveats apply), and in some agricultural circles the spider is favoured as a predator of pests. For example, in parts of Kochi it is known as ineushiwaka, or “Ushiwaka of the rice” (a reference to Ushiwakamaru, the childhood alias of warlord-cum-folk hero Minamoto no Yoshitsune)
These spiders have a single-year life cycle, and time for the adults to die is rapidly approaching as I write this. Their eggs will already have been laid in their egg sacs – about 900 per sac – and will hatch next spring. By August, the next generation of mature adults will be with us.