Ant-eating twigs and stalks: the natural prey of Tmarus and Monaeses (Araneae: Thomisidae) in the Western Palaearctic, analysed by using online-accessible wildlife photography

Tobias Bauer

doi:10.30963/aramit6206

Abstract

The diet of the Western Palaearctic species of the closely related crab spider genera Tmarus Simon, 1875 and Monaeses Thorell, 1869 is only little known. A quantitative analysis of images showing spiders with prey, collected from the World Wide Web and the literature, suggests that both genera mainly prey on ants (Hymenoptera: Formicidae), while occasionally capturing other arthropods, such as spiders (Araneae). Most images depict feeding spiders that hold ants anterior-dorsally at the articulation of head and pronotum. Tmarus galapagosensis Baert, 2013, from the Galapagos Islands, is known to attack ants by a bite to this region, which, in combination with the photographic evidence, supports the hypothesis that Western Palaearctic representatives of both genera attack ants in a similar way. Three species of Tmarus and two of Monaeses were identified from the images feeding on ants, demonstrating that probably all species of both genera at least include ants in their diet. In conclusion, Western Palaearctic Tmarus and Monaeses are myrmecophagous predators and probably have a narrow trophic niche in nature. Furthermore, both genera represent interesting model organisms for the study of trophic specialisation in widespread taxonomic clades.

Highlights

While most spiders are considered opportunistic predators, at least to some extent (e.g. Mezőfi et al 2020, Nentwig 1987, Pekár et al 2012), trophic specialisation is only found in a comparably small number of species (Pekár et al 2012, Pekár & Toft 2015)
Not much is known about the ecology of both genera, but Lubin (1983) analysed the diet of Tmarus galapagosensis Baert, 2013 from the Galápagos Islands (sub Tmarus cf. stolzmanni Keyserling, 1880; see Baert (2013) and the footnote in Lubin (1983: 83)), which was observed to feed exclusively on native ants
For Monaeses, a quantitative analysis of their diet is absent, but an observation from Sicily suggests a similar myrmecophagous behaviour (Dentici & Amata 2018). Because both genera are difficult to observe in the field, mostly due to their cryptic pattern and reclusive behaviour (Dippenaar-Schoeman 1984, 1985, Tang & Li 2009), onlineaccessible wildlife photography of specimens holding prey in their chelicerae provides a valuable source of information on

Summary

Introduction

While most spiders are considered opportunistic predators, at least to some extent (e.g. Mezőfi et al 2020, Nentwig 1987, Pekár et al 2012), trophic specialisation is only found in a comparably small number of species (Pekár et al 2012, Pekár & Toft 2015). The widespread and species-rich genus Tmarus Simon, 1875 is mostly found on branches of shrubs and trees, potentially imitating mosscovered or dried out twigs (Ileperuma Arachchi & Benjamin 2019) or leaf stumps (Roberts 1995), while Monaeses Thorell, 1869 mostly inhabits grassland and low vegetation (Dippenaar-Schoeman 1984). I present an analysis of the natural diet of both genera based on online accessible images from various internet sites and databases and demon strate that both genera primarily (but not exclusively) prey on ants in their natural habitats

Methods

Results

Discussion

Conclusion