Females are poisonous, while males and juveniles are harmless. The normally passive spiders deliver a poisonous bite when disturbed. Less than 1 percent of black widow bites are fatal. Putting hydrogen peroxide on a black widow spider bite can protect against infection. In some cases, an antidote is used.
Most adults recover completely from the poisonous bite in two to five days.
Mayumi Yamamoto contributed to this report.