Kanagawa Shinbun reported that a red back spider was found in a field of a company in Tsurumi, Yokohama. This is the first case in Yokohama while the spiders were already found in Atsugi and Kawasaki.
If you get bitten by the spider, you feel pain and it might cause a cramp. It will cease in a few days but you might have severe symptoms. If you are bitten, please see the doctor and bring the dead spider (that bit you) if possible so that the doctor will know what type of spider it is.
Do not touch the spider with a bare hand/foot. It is advised to kill it by trampling with your shoes on.
The article on Kana Loco by Kanagawa Shinbun (Japanese)
The warning from Kanagawa prefecture (Japanese)