Fourlegs, the night I first met him.
Dropping the legs has been done voluntarily by the spider. The ability for a spider to decide to drop the leg is called autotomy, which is under the spider's control. Apparently they don't do it under anaesthesia. Muscles close over the joint, the haemolymph (blood) pressure then presses on the joint membrane and seals the wound.
To drop four legs, poor Fourlegs must have been in a tight spot - either something had caught his legs, or he had trouble extracting them when moulting - so the legs are still in the shed skin. If bitten by a wasp or bee, the spider can drop the leg before the venom gets to its body. I don't know Fourlegs' story, but given it was four at once on one side, I am tending to believe it was a moulting mishap.
If Fourlegs moults again, then the legs will regrow, although they will probably be smaller and weaker. But at least he'll have them. If he's an adult, then this is it for life.
I've seen lots of spiders with seven legs, a few with six and even occasionally five. But never four. And all on the same side looks horrible.
The good news!!! Fourlegs was feeding last night. You can see the mashed black thing he is holding to his mouth, which is on the underside of his front section, his cephalothorax. He is using his left palp over on the right side and often seems to balance by bringing his left foreleg right across.
Fourlegs feeding, on the second night.
He also seems to have spun some silk around and is using it to help maintain balance. He looked very weird with his legs in a strange position, and hanging suspended, but I wonder if it was the only way he could hold his prey. I was sure he was dying, but he was there again tonight, and all is well.
Fourlegs balancing to feed.
He has been out for three nights now - so has survived this way for at least three days. Not far from the same spot. I will keep you updated if I see him again.
Just in case you want a lovely photo to finish on, I did manage to photograph a spider of the same size and species a few nights earlier, about ten metres from Fourlegs' current location. I have decided that it was him - because I want to. Don't look too closely and spoil my delusion. The rose thorn gives you an idea of his size.
Please don't make any gory or sick jokes about my spider. I am extraordinarily fond of Fourlegs and desperately want him to survive, moult and have to be renamed Eightlegs.