From late summer throughout autumn, Joro spiders (上臈蜘蛛, Jorōgumo) are very visible in the Futamurayama forest with their big webs across the paths. Also, around Fujita Health University, in trees but also between buildings, they are easily found. Just now, as it started to freeze at night, the last ones have gone. They survive as eggs, laid by the females which swell up (compare Fig. 1 with Fig. 2) at the end of autumn and are much bigger than the males. In spring, the newborn spiders weave a thread with a “parachute” at the end for the wind to carry them to new pastures.
In the last few months, I have taken some pictures of them shown below. They are friendly spiders who just go about their business. The females have beautiful irradiant yellow/greenish and red colors, mixed with pitch-black, and I even heard them described as “fluorescent” which is probably not correct but understandable.
(from Wikipedia) Jorōgumo is a legendary creature in Japanese folklore. A Jorōgumo is a spider who can change her appearance into that of a beautiful woman. She’s said to breathe fire and to be able to control other spiders. She seeks men to seduce, whom she then binds in her silk and devours.
Regardless of that story, I read that the Joro spider females do not devour their males. However, the males—of which usually one or two, sometimes three, reside in her web, always on the opposite side of the plane of the orb-web—seem not to understand that, and stay at a respectful distance. The mating is quite fast, probably because of the fear of the male to be eaten, and I have seen them wait until the female has some (other) prey. When winter comes, most males disappear a bit earlier than the females, but I don’t know why that is.
The web can be huge (several meters) and has a central orb with at both sides structures that appear to strengthen the web and are also used for walking. Fig. 8 shows a video of a Joro spider that is very tidy by bringing an encapsulated prey to the “storage” space of her web, as to not let flying insects see her web too easily. However, I have seen the web of other Joro spiders to be messy throughout (e.g., Fig. 2). Maybe it has to do with blending in with the forest or sky, maybe with the material that enters the web (leaves or prey?), or maybe those are just personal differences between individual spiders?
It is nice to have these beautiful spiders around, although in the forest their webs can be a nuisance.
