THE ANIMAL FILES

Mediterranean black widow

Latrodectus tredecimguttatus

Thirteen spots are a clue, not a complete identification.

The Mediterranean black widow has thirteen abdominal spots, usually red but sometimes orange or yellow. Adult females are larger than males, and the species lives in steppes and other grasslands.[1]

Follow the evidence ↓
Mediterranean black widow
Image: No machine-readable author provided. Kork~commonswiki assumed (based on copyright claims). · Commons · Public domain
Spots with variation
Red, yellow or orange markings[1]
Not one adult size
Females are larger than males[1]
Habitat
Steppes and other grasslands[1]

Spots with variation

The upper abdomen has thirteen spots, usually red but sometimes yellow or orange. The species name refers to this spotted appearance.[1]

Not one adult size

Adult females are larger-bodied than males, so a small adult and a larger adult may belong to the same species.[1]

A grassland spider

This species occurs in steppes and other grasslands.[1]

A COMMON MIX-UP

Do orange rather than red spots automatically exclude this species?

No. Its abdominal spots may be red, orange or yellow.[1]

TRY A LITTLE REASONING

Why would size alone be a weak way to separate two adults?

Reveal the explanation

Females and males differ in body size. Sex must be considered before treating adult size as a species boundary.[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 — Mediterranean black widow (cited revision)
  2. NCBI Taxonomy — Latrodectus tredecimguttatus

Last fact check:

One discovery leads to another

Southern black widowA tangled web is organised around catching and wrapping.Latrodectus mactans ↗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 ↗