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Central-eastern Wheatbelt Shield-backed Trapdoor Spider (Idiosoma mcnamarai)

The Central-eastern Wheatbelt Shield-backed Trapdoor Spider is an Australian mygalomorph spider in the genus Idiosoma. It is known from the central-eastern Avon Wheatbelt of Western Australia, but its precise habitat and ecology are poorly known. It is listed as Priority 1 on the DBCA WA priority fauna list, so works in its known range should include cautious survey and pre-clearance planning.

Conservation status

Western Australia, WA Threatened and Priority Fauna List: Priority 1.

Seasonal planning

Species-specific seasonal activity, movement and breeding information has not been documented. The planning row below is a general prompt, not evidence of seasonal activity.

Seasonal activity: Not documented for this species.

Breeding period: Not documented for this species.

Species-specific months are not known.

  • All planning periods: Planning window only. Do not assume that survey detectability or activity is uniform across the year; species-specific seasonal information is not available.

Identification: Appearance and size

This is a poorly known shield-backed trapdoor spider, and species-specific field identification information is limited.

The species is a mygalomorph spider in the family Idiopidae and genus Idiosoma. Its body size and detailed field description have not been documented.

Idiosoma are described as having enlarged, hardened abdominal sigilla associated with shield-backed form and phragmotic defence. This is genus-level information, not a complete diagnostic description of this species.

Identification: Similar species

Idiosoma formosum is identified as a close sister species in the taxonomic study. Field characters to reliably distinguish the two are not documented.

Refer photographs or specimens to a suitably experienced arachnologist where species-level confirmation is needed.

Identification: Field signs

No species-specific burrow description or other field sign has been documented.

Idiosoma are generally described as burrow-dwelling. Record possible burrow signs cautiously and do not identify them as this species without supporting evidence.

Distribution: Known range

The known range is in Western Australia’s central-eastern Avon Wheatbelt. Few records are known, so the mapped range may not represent the full distribution.

The species is reported from the central-eastern Avon Wheatbelt bioregion. Trayning, 236 km east of Perth, is the type locality.

Atlas of Living Australia records show 10 Western Australian records at six distinct 0.1-degree locations, between latitude -31.9 and -30.1 and longitude 117.6 and 118.1. Records outside Western Australia were excluded as likely errors.

Distribution: WA regions and status

The DBCA priority fauna list flags the Wheatbelt region for this species. It is listed as Priority 1, is poorly known, and is known from few locations, none of which are on conservation lands. Priority 1 is a DBCA priority category, not a threatened-species listing under the Biodiversity Conservation Act 2016.

Habitat: Recorded habitat

The species is known from the central-eastern Avon Wheatbelt, but its site-level habitat has not been documented.

No vegetation type, soil, landform or microhabitat has been documented for this species. Do not infer habitat suitability from the regional name alone.

Habitat: Site assessment

At a development site within the known region, assess the actual ground conditions and record vegetation, soil surface, landform and disturbance history. These observations can help improve knowledge but are not established habitat requirements for the species.

Foraging habitat: Known information

Species-specific foraging habitat and diet have not been documented.

Prey items, foraging period and species-specific foraging habitat have not been documented for Idiosoma mcnamarai.

Foraging habitat: Genus-level context

A general account of Idiosoma describes spiders detecting prey that disturbs trip-lines around a burrow entrance. This behaviour is not confirmed for Idiosoma mcnamarai, so treat possible trip-lines or burrow approaches as general search cues only.

Breeding habitat: Known information

Breeding sites, behaviour and timing have not been documented for this species.

Egg sacs, egg numbers, mating and juvenile development have not been reported for Idiosoma mcnamarai.

Breeding habitat: Precaution

Do not apply breeding dates or assumed breeding-site features from other Idiosoma species to this species. Treat any suspected occupied burrow as potentially important habitat and seek specialist advice before disturbance.

Sheltering habitat: Known information

Burrows are described for the genus generally, but the form and dimensions of this species’ shelter have not been documented.

The shelter or burrow of Idiosoma mcnamarai, including its depth, entrance form and construction, has not been documented.

Sheltering habitat: General group guidance

Idiosoma are described as burrow-dwelling. Avoid probing, excavating or covering possible burrow entrances while checking ground surfaces. These are precautionary actions for trapdoor spiders generally, not confirmed species-specific requirements.

Threats: Known pressures

The species is poorly known and recorded from few locations. Specific threats have not been identified.

The species is known from few locations, none of which are on conservation lands. No species-specific threat process has been identified.

Threats: Avoid assumptions

Threats discussed for other Idiosoma species in the Avon Wheatbelt are not established for Idiosoma mcnamarai. Record observed site pressures, but do not present them as confirmed threats to this species.

Survey methodology: 1. Desktop assessment

Taxon-specific survey methods and detectability have not been documented. Use cautious ground-based survey practices and treat non-detection as inconclusive.

Check whether the site lies within the known central-eastern Avon Wheatbelt range and review available occurrence information. Few published records are known, so do not assume the species is absent because no records are mapped.

Survey methodology: 2. Ground inspection

As general trapdoor-spider survey practice, inspect suitable undisturbed ground carefully for possible burrow entrances and associated surface signs. Avoid disturbing suspected burrows during initial inspection.

Record survey effort, date, conditions, location, photographs and the basis for any identification. The optimal survey season, detection rate and species-specific signs have not been established.

Survey methodology: 3. Identification and escalation

Do not identify a burrow as this species from appearance alone. Seek specialist assessment where a possible animal or burrow is found, and follow applicable permit and fauna-handling requirements.

Vegetation associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific vegetation association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Ecosystem associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific ecosystem association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Soil and substrate associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific soil association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Water and wetland associations

Source-checked associations and automatically indexed candidates are separated below. An association does not establish site presence, preference or dependence.

No species-specific water association has been indexed or source-checked in this evidence library. This is an evidence gap, not evidence of no association.

Fauna records and mapped habitat: Not yet analysed

Record locations can be overlaid with mapping, but record frequency alone does not measure habitat preference. No species is excluded from desktop assessments by this analysis.

No quality-controlled record-to-map analysis has been completed for this species. The existing generalised distribution dots and indicative range polygons have not been treated as precise occurrence coordinates.

A defensible run needs dated, independently attributable records, coordinate uncertainty, duplicate and captive-record checks, layer versions and regional scope. Preference and absence require additional survey-effort and detection evidence.

Habitat limitations and contrary evidence: No supported exclusion recorded

Not recorded is not the same as cannot occur. Low suitability, resident habitat, breeding habitat and occasional movement are different conclusions.

This library has not established a vegetation, ecosystem or soil-type exclusion for this species. This does not mean all habitat is suitable; the evidence needed to justify an exclusion has not been assembled.

Habitat limitations and contrary evidence: Before using a negative association

  • Confirm the taxon, geographic region, life stage and habitat function covered by the evidence.
  • Check survey methods, season, repeated effort and detectability before interpreting non-detection.
  • Investigate credible contradictory records and microhabitats absent from broad mapping.
  • Do not convert a missing map class, low record count or failed data request into species absence.

Before habitat disturbance: 1. Check records and risk

Plan early because the species is poorly known and recorded from few locations.

Review the proposed disturbance footprint against known records and the central-eastern Avon Wheatbelt range. Arrange appropriately experienced ecological input where habitat disturbance is proposed in the known region.

Before habitat disturbance: 2. Survey and site controls

Undertake a careful pre-disturbance ground inspection and clearly report the limitations of survey detectability. Mark potential burrows or areas requiring further assessment, and keep machinery and vehicle movement away until they have been checked.

Brief clearing crews on the possibility of inconspicuous ground-level burrows and the requirement to stop work and notify the fauna spotter catcher if a suspected spider or burrow is encountered.

During habitat disturbance: 1. Stop and protect

Use a cautious stop-and-check response if a possible spider or burrow is encountered during works.

Pause disturbance in the immediate area, keep people and machinery clear, and prevent the suspected burrow from being crushed, filled or excavated while it is assessed.

During habitat disturbance: 2. Assess and record

Have the fauna spotter catcher or ecologist document the location and condition of the sign and seek specialist identification where needed. Do not assume that a burrow is occupied or unoccupied without evidence.

During habitat disturbance: 3. Follow approvals

Proceed only in line with project approvals, applicable fauna-handling requirements and advice from the responsible environmental manager. Do not relocate or handle a spider unless authorised and suitably qualified.

After habitat disturbance: 1. Record the outcome

After an encounter or disturbance, retain records and review whether further site action is needed.

Document the location, evidence, identification confidence, actions taken and any area temporarily protected. Share verified records through the project’s agreed reporting pathway.

After habitat disturbance: 2. Review remaining works

Before restarting nearby work, check that the environmental manager has reviewed the observation and any specialist advice. Extend precautionary controls if the evidence or uncertainty warrants it.

Rehabilitation actions: 1. Protect retained ground

Species-specific rehabilitation requirements have not been documented. Rehabilitation should not be assumed to replace occupied habitat.

Where ground is retained, prevent avoidable compaction, excavation or material placement in areas identified for protection. Keep rehabilitation activities from damaging any suspected burrows.

Rehabilitation actions: 2. Restore cautiously

Use the site’s approved rehabilitation plan and retain locally appropriate ground conditions where required by that plan. Preferred revegetation, soil treatments and habitat restoration methods for this spider have not been identified.

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