Black Widow vs False Widow

The quick tellA black widow is glossy black with a red hourglass underneath. A false widow is brown to purplish, has no hourglass and its abdomen often shows pale marks.
Black widow (Latrodectus mactans, L. variolus, L. hesperus)

Photo (Southern black widow): Kazvorpal, CC BY-SA 4.0, via Wikimedia Commons

Black widow

Medically significant · Latrodectus mactans, L. variolus, L. hesperus

  • Shiny black female with a round abdomen
  • Red hourglass or two red marks under the abdomen
  • Messy, strong web low to the ground, often in garages, wood piles and water meters
  • Males are small, brown and harmless

Size: 0.5–0.6 in. Habitat: Dark, dry, undisturbed spots: wood piles, sheds, crawl spaces, under outdoor furniture.

Venom affects nerves and can cause strong muscle pain and cramps. Deaths in the US are very rare.

False widow (Steatoda grossa)

Photo: Ken Kneidel, CC0, via iNaturalist

False widow

Harmless · Steatoda grossa

  • Round dark brown to purplish abdomen, no red hourglass
  • Faint pale marks on the back in some
  • Messy web in sheds and window frames

Size: 0.25–0.4 in. Habitat: In and around buildings, mostly along the coasts.

Bites are rare and mild.

Where each one lives

Alabama: Black widow onlyAlaska: neitherArizona: Black widow onlyArkansas: Black widow onlyCalifornia: both live hereColorado: Black widow onlyConnecticut: Black widow onlyDelaware: Black widow onlyFlorida: Black widow onlyGeorgia: both live hereHawaii: neitherIdaho: Black widow onlyIllinois: Black widow onlyIndiana: Black widow onlyIowa: Black widow onlyKansas: Black widow onlyKentucky: Black widow onlyLouisiana: Black widow onlyMaine: Black widow onlyMaryland: Black widow onlyMassachusetts: Black widow onlyMichigan: Black widow onlyMinnesota: Black widow onlyMississippi: Black widow onlyMissouri: Black widow onlyMontana: Black widow onlyNebraska: Black widow onlyNevada: Black widow onlyNew Hampshire: Black widow onlyNew Jersey: Black widow onlyNew Mexico: both live hereNew York: Black widow onlyNorth Carolina: both live hereNorth Dakota: Black widow onlyOhio: Black widow onlyOklahoma: Black widow onlyOregon: both live herePennsylvania: Black widow onlyRhode Island: Black widow onlySouth Carolina: Black widow onlySouth Dakota: Black widow onlyTennessee: both live hereTexas: Black widow onlyUtah: Black widow onlyVermont: Black widow onlyVirginia: both live hereWashington: both live hereWest Virginia: Black widow onlyWisconsin: Black widow onlyWyoming: Black widow only
Black widow: 48 states. False widow: 8 states. Both live in 8 states.

Side by side

Black widowFalse widow
DangerMedically significantHarmless
Size0.5–0.6 in0.25–0.4 in
States488
HabitatDark, dry, undisturbed spots: wood piles, sheds, crawl spaces, under outdoor furnitureIn and around buildings, mostly along the coasts

Questions

How can you tell a black widow from a false widow?

A black widow is glossy black with a red hourglass underneath. A false widow is brown to purplish, has no hourglass and its abdomen often shows pale marks.

Which one is dangerous?

The black widow: medically significant. The false widow: harmless. If you are not sure, keep your distance and do not handle it.

Where do both live?

Both live in 8 states: California, Georgia, New Mexico, North Carolina, Oregon, Tennessee, Virginia and Washington.

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