Context. Bioindicators are used for conservation prioritisation by means of spatial comparisons of a site value, or monitoring of ecosystem recovery or response to management. Spiders are characterised by their selection of quality habitats and guild responses to environmental change. However, they have only occasionally been used as bioindicators. Grammostola vachoni is an endemic tarantula that only occurs in the grasslands of the mountainous system in central Argentina and it is included in the Red List of the IUCN as Vulnerable.

Aims. In this study, we performed a characterisation of the microhabitat of G. vachoni at sites with different disturbance regimes and we analysed the potential use of this species as a bioindicator of mountain grassland health.

Methods. We determined the microhabitat characteristics around their refuges by mean of the soil parameters, as well as the composition and structure of vegetation and amount of refuge available.

Key results. We found significant differences in the number of individuals and the percentage of occupation between sites. No significant differences were recorded in the soil characteristics and occupation of G. vachoni but we found that the composition of vegetation, and the heterogeneity and diversity of plants are influenced by different disturbance regimes, altering the distribution of spiders.

Conclusions. Our results are consistent with those of other studies where the spiders have proved to be good bioindicators of different disturbances and we propose for the first time a Theraphosidae species for evaluating the state or health of a natural grassland.

Implications. The information reported in this study is very important to provide data for a future re-categorisation of G. vachoni for the Red List of IUCN. Also, we add new component of ecosystems for to use as indicator, open up the possibility for new research for the same and other species of a grasslands of the mountainous system.