Idiosoma nigrum
Shieldbacked Trapdoor Spider Identification in Australia
A Western Australian trapdoor spider with a hardened abdominal shield. The revised Idiosoma nigrum species must be separated from its close relatives.
Avoid handling; bite effects uncertainAbout Shieldbacked trapdoor spider
Idiosoma nigrum is one of the shield-backed trapdoor spiders of Western Australia. The unusual hardened abdomen can help block access inside the burrow. This protective structure is a more useful clue than the ordinary dark body colour, but it is not unique to this species.
A major revision separated several related species that had previously been confused under a broad nigrum concept. Consequently, an old map or an image labelled shield-backed spider may refer to another Idiosoma. Use the current species concept and expert identification before applying a species name. A distant view of a retreat or a wandering male will often support only a broad trapdoor comparison. Never extract an animal to inspect its shield or open the burrow: the retreat is integral to its survival. Keep the local habitat undisturbed and record observations without publishing precise burrow locations.
Identification limit: this guide is a comparison aid. A name match in the identifier does not establish a species record.
Compare similar spiders
Sources and further reading
- Rix and colleagues: revision of shield-backed Idiosoma
- Australian Museum: spider survival and burrow defence
- Healthdirect: spider-bite first aid
Reviewed 21 September 2026. Identification guide; not a confirmed species diagnosis.
Quick identification
- Western Australian locality
- Mygalomorph body and silk-lined burrow
- Hardened abdominal shield when naturally visible
- Other shield-backed Idiosoma require specialist separation
What to check next
Photograph the whole spider and its surroundings without disturbing it. Use the clues together; a close match is not a confirmed species identification.
When to seek medical help
Do not handle or probe the retreat. If a bite could be from a funnel-web or mouse spider, call 000 and follow pressure-immobilisation first aid. Do not wait for identification. Poisons advice: 13 11 26.
Where it is usually seen
Western Australian ground habitats within the revised species range. Older, broader nigrum-group records include other species and need rechecking.