Introduction
Finding food is an important component of the animal behavior, encompassing on average more than 50% of their lifetime activity budget (Fennessy 2004). Predation is an important technique to acquire food (Kie 1999; Bertram 1979), and occurs between many different taxa, such as vertebrates preying on other vertebrates, for example a bird preying on a gecko (Koski and Merçon 2015; Lopes et al. 2005), snakes feeding on lizards (Raselimanana 2018) and amphibians catching amphibians (Rasolonjatovo et al. 2018), or between vertebrates and invertebrates, for example a bird eating a butterfly (Collins and Watson 1983; Pinheiro and Cintra 2017; Bowers et al. 1985; Stefanescu 2000; Olofsson et al. 2010; Su et al. 2015). However, invertebrates can also prey on vertebrates thereby turning around the “expected order”. Reported cases are geographically widespread and highly diverse: for example, crabs preying on frogs (Pyke et al. 2013; Rosa et al. 2014), dragonfly larvae (Barej et al. 2009) and water scorpions eating tadpoles (von May et al. 2019), water bugs preying on fish (von May et al. 2019), praying mantis feeding on lizards (Jehle et al. 1996) and carabid beetles as well as spiders feeding on amphibians (Wizen & Gasith, 2011; von Mayet al. , 2019).
Spiders are among those invertebrate predators which have also been reported to prey on vertebrates (Menin et al. 2005; Costa-pereira et al. 2010; Gaiarsa et al. 2012; Amaral et al. 2015; Kirchmeyer et al. 2017). Most reports have documented spiders to catch their vertebrate prey underwater (Bovo et al. 2014; Amaral et al. 2015; Folly et al. 2017; Kirchmeyer et al. 2017) or by active terrestrial hunting (Maffei et al. 2010; Kirchmeyer et al. 2017). Exceptionally large orb-weaver spiders can catch vertebrates such as bats, birds and amphibians in their web (Muscat et al. 2014; Kirchmeyer et al. 2017; Toledo 2005; Folt and Lapinski 2017; Nyffeler and Kno 2013). However, insect usually represent a larger proportion of spider prey than vertebrates, making the latter a welcome bycatch but not the main target (Kirchmeyer et al. 2017).
Generally, amphibians seem to be the favorite vertebrate prey of spiders (Fadel et al. 2019; Toledo 2005; Pedrozo et al. 2017), probably due to their soft skin (Duellman and Trueb 1986) but also due to their small to moderate size. In addition, amphibians are also preyed on by a variety of other animals (Koski and Merçon 2015; Ceron et al. 2017) and even carnivorous plants (Duellman and Trueb 1986; Bovo et al. 2014; Ceron et al. 2017).
Here, we report on a specialized trapping technique of a spider to catch amphibians as the main prey - a behavior that is, to the best of our knowledge, new to science. The predation occurred between a spider of the genus Olios sp. and a small amphibian (Heterixalus andrakata, Glaw and Vences, 1991, Least Concern) in north-eastern Madagascar. To our knowledge, this is also the first report of spider predation on amphibians in Madagascar.