Southern black widow or false black widow?
These two get mixed up often. The southern black widow is rated Get advice and the false black widow is rated Be careful, so it is worth a closer look.
Why people mix them up
Both are shiny, dark, round-bodied cobweb spiders that hang upside down in messy webs in garages, sheds and corners. In a dim garage, a dark round spider is easy to assume is a widow. The false black widow has also spread widely, so it now turns up in many of the same places.
Turn it over gently with a stick or look at it from below in its web. A red or orange hourglass on the underside, whole or split in two, points to a widow. No hourglass, plus a brownish or purplish tint and pale marks on top, points to the false black widow.
Southern black widow
Photo: Maura, CC BY 4.0, via iNaturalist
Size: Adult female body about 8–13 mm (about 1/3 to 1/2 inch), roughly 1.5 inches with legs spread; males about 3–6 mm (1/8 to 1/4 inch)
- Adult female is glossy jet black with a round, bulbous abdomen
- Red or orange hourglass on the underside of the abdomen, with the two halves joined in the middle
- Often a red spot just above the spinnerets on the top of the abdomen
- Messy, tangled, very strong web built low to the ground in a dark corner
- Round grayish-tan egg sac with a small point on top
A bite from an adult female can cause strong, spreading muscle pain and cramps, so get medical advice right away if you think you were bitten.
False black widow
Photo: kenkneidel, CC0, via iNaturalist
Size: Adult female body about 6–10.5 mm (1/4 to 3/8 inch); males smaller, about 3–5 mm (1/8 to 1/5 inch)
- Shiny dark purplish-brown to nearly black, round to oval abdomen
- No red hourglass on the underside
- Often faint pale yellowish or grayish marks or a thin band on the top of the abdomen
- Reddish-brown front body and slightly darker legs
- Hangs upside down in an untidy cobweb in a corner, cupboard or under furniture
Not a true widow: a bite can hurt and swell for a day or two, but it is far milder than a black widow bite.
How to tell them apart
- Glossy jet black with a red or orange hourglass on the belly; false black widows have no hourglass and are more brownish or purplish.
Still not sure? Use the picker, and if a bite worries you, call Poison Help at 1-800-222-1222.