THE ANIMAL FILES

Southern black widow

Latrodectus mactans

A tangled web is organised around catching and wrapping.

Southern black widows catch prey in three-dimensional webs, wrap it in silk and use venom and digestive enzymes before feeding. Adult males, females and young spiders differ in appearance.[1]

Follow the evidence ↓
Southern black widow
Image: Kazvorpal · Commons · CC BY-SA 4.0
Web form
A three-dimensional tangled cobweb[1]
Adult female
Often shiny black with a ventral red hourglass[1]
Egg shelter
A rounded silken sac[1]

Appearance changes with age and sex

An adult female usually has a rounded dark abdomen and a red hourglass marking underneath. Juveniles have a different pattern, including pale stripes and coloured spots, and males are smaller.[1]

Silk works before the bite

The web is a three-dimensional tangle rather than a flat circular orb. Once prey becomes caught, the spider emerges from its retreat and wraps it securely before biting. Silk and venom act at different points in the sequence; the visible web is an active part of a feeding system.[1]

A menu broader than flying insects

Prey includes insects but also woodlice, millipedes and other arthropods. After prey is subdued, digestive enzymes help break it down before the spider finishes feeding in its retreat. Egg sacs use silk for another task: enclosing and protecting the developing young rather than catching a meal.[1]

A COMMON MIX-UP

Does every black widow look like the familiar adult female?

No. Young spiders and males can differ markedly in size and markings. The adult female’s red hourglass is an important part of the familiar image, but it should not replace attention to age and sex.[1]

TRY A LITTLE REASONING

Why wrap prey that has already been caught in a web?

Reveal the explanation

Catching and securing are distinct steps. Additional silk holds the struggling animal while the spider proceeds with biting and digestion, so an initial entanglement is not the end of the feeding process.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Southern black widow (fixed revision; adapted and translated)
  2. NCBI Taxonomy — Latrodectus mactans (identity and classification)

Last fact check:

One discovery leads to another

Mediterranean black widowThirteen spots are a clue, not a complete identification.Latrodectus tredecimguttatus ↗Wasp spiderThe stripes resemble a wasp; the prey-catching machine is silk.Argiope bruennichi ↗Northern golden orb weaverThe large spider and the tiny one on a web can be female and male of the same species.Nephila pilipes ↗