1 INTRODUCTION
The Iranian scorpion fauna is considerably diverse, comprising 68 valid species belonging to 19 genera and four families, with 60.3% (41 species) endemic to the country (Barahoei et al, 2020). These predatory, nocturnal arachnids are more frequent in the arid to semi-arid parts of southern Iran. Scorpionism is an important public health problem in Iran, and 40,000 to 50,000 cases of scorpion stings are estimated to occur per year in the country (Dehghani, et al. 2018). However, studies on Iranian scorpions have been scattered and mostly focused on their taxonomy and distribution. Recently, some ecological studies have also been conducted on scorpions in Iran (e.g. Mirshamsi 2013, Gholizadeh et al. 2016, Motevalli-Haghi et al. 2018, Rafinejad et al. 2020, Kassiri and Yousefi 2021, Navidpour et al. 2021, Soltan-Alinejad et al. 2021). Nevertheless, none of these studies tested the pitfall trapping method.
To date, about ten different methods have been used to collect scorpions, including stone rolling, pitfall trapping, water-pan traps, using UV light, destroying mud walls, pouring water into scorpion burrows, excavating channels, using rubber bands, using soaked cloth as traps, and collecting scorpions by stung patients (Dehghani et al. 2019).  Dehghani et al. (2019) evaluated different methods, except pitfall trapping, for collecting these arthropods in Khuzestan province, and their results showed that using UV light and turning stones were the most efficient methods for collecting scorpions at night and during the day, respectively.
Collecting the largest possible number of specimens of a particular animal or group of animals can provide a more reliable estimate of actual species diversity. For this reason, optimization of collection devices is very important, especially in the case of pitfall trapping, which is one of the common and widely used methods for collecting ground-active arthropods (Brown and Matthews 2016).
Pitfall traps are inexpensive, easy to use and efficient, and they collect large samples suitable for statistical analyses (Spence & Niemelä, 1994). Pitfall traps operate continuously from installation to collection (Stašiov, et al. 2021), which can be particularly useful when studying the numbers and activity of surface-dwelling invertebrates. Nevertheless, the efficiency of this sampling method for collecting scorpions and also effects of different pitfall trap designs on the number and species composition of the captured scorpions have received little attention hitherto. The aim of our study is to compare the collection efficiency of different pitfall trap designs to capture the largest number of species and individuals of scorpions.