4 Discussion
Pitfall trapping is considered an important method for collecting scorpions (Williams 1968, Druce et al. 2004, Shehab et al. 2011; Dehghani et al. 2019). Capture efficiency of pitfall traps, for collecting ground-active invertebrates, can be affected by trap material (Luff, 1975), use of trap covers (Spence & Niemelä, 1994), trap shape (Spence & Niemelä, 1994), size of trap diameter, preservative solutions, use of funnels, sampling intervals, and distance between adjacent traps (Brown and Matthews 2016). Our work is considered the first study to compare the effects of different pitfall trap designs on their efficiency in collecting scorpions. Williams (1968) also used pitfall traps to collect scorpions, but only studied the effects of cover on the catch rate of the traps.
Placing cover over pitfall traps can prevent rain and plant litter from entering the traps and escape of the trapped animals; it can also reduce dilution of the preservative fluids (Császár et al. 2018). In addition, using covers can prevent large vertebrates from trampling the traps, reduce bycatch of small vertebrates, and deter vertebrates from eating the trapped specimens (Hohbein and Conway 2018). Scorpions typically hide under rocks or in burrows during the day and emerge after sunset. They hunt at night for small animals, usually invertebrates, and explore spaces under objects like rocks and logs (Farzanpay 1987), maybe in search of their prey or to find shelter. These behavioural characteristics may explain the significantly higher number of scorpions caught with covered pitfall traps in the present study. Our result regarding the significant positive effect of trap covers on the number of scorpions captured agrees with the results of Williams (1968). However, our result is not in line with that of Buchholz and Hannig (2009), who found no differences between covered and open traps, although their study was conducted mainly on insects and spiders. These different results suggest that using covers may have different and even opposite effects on catch rate of pitfall traps for various arthropod groups.
Our results indicate that utilising funnels has no significant effect on the number or species of scorpions captured. Lange et al. (2011) also showed that the use of funnels did not significantly affect the number of captured beetles and spiders, while funnel traps captured fewer small mammals than cup traps. Nevertheless, we recommend using funnel traps because our results, which are consistent with those of Pearce et al. 2005, Lange et al. 2011, and Radawiec and Aleksandrowicz 2013, show that the use of funnels reduces the likelihood of unwanted bycatch of small vertebrates.
The results show that larger traps (15 cm) captured more individuals than smaller traps (10 cm), which is consistent with the results of Ward et al. 2001, Lange et al. 2011 and Stašiov et al. 2021. Despite the positive effect of a larger trap diameter on the total catch, it may have the disadvantage of increasing the probability of catching small vertebrates (Stašiov et al., 2021). To overcome this disadvantage, we recommend using large funnel traps, each equipped with a cover, as the use of funnel and roof may reduce the likelihood of unwanted capture of small vertebrates.
The results also show that more scorpions were captured in May than in March and April (Figure 7), which may indicate the positive effect of higher temperatures on their activity. Pitfall trap catches can be used to estimate activity density of ground dweller animals (Brown and Matthews 2016), and climatic factors can influence activity (Saska et al. 2013).
Several authors have acknowledged the need for standardization of pitfall trapping methods (Adis 1979, Koivula et al. 2003, Hancock and Legg 2012, Radawiec and Aleksandrowicz 2013 and Brown and Matthews 2016). These authors reasoned that using standardized pitfall traps is essential for conducting comparable ecological studies focused on the spatial and temporal distribution of the ground-dwelling animals and would allow for more synthetic analyses. Based on their literature review, Brown and Matthews (2016) proposed a standardized pitfall trap for collecting different arthropod groups with the following details: a trap made of a transparent plastic cup with a diameter of 9-11 cm; with an internal sampling pot containing a nontoxic solution; and equipped with a funnel and a cover. Nevertheless, the proposed trap design would be most effective for capturing ants, spiders and beetles (Brown and Matthews 2016). However, the question remains whether it is practical to use a ”standardised” trap type for the study of different arthropod taxa.
In contrast to the authors who support using a standardized pitfall trap for various animal groups, especially invertebrates, Császár et al. (2018) have shown that the efficiency of trap designs depends on the target taxa (e.g. spiders vs carabid beetles). Therefore, it seems that the standardized traps should be designed only for animal groups with similar biological, behavioural and ecological characteristics. Based on our results, we suggest that the optimal trap for scorpions should be a plastic cup with an opening diameter of about 15 cm, equipped with a funnel and a plastic cover. A schematic design of the proposed pitfall trap according to our study is shown in Figure 11. It should be noted that this design may be ideal for collecting scorpions in regions with arid to semi-arid climates. However, most scorpion species live in arid and semi-arid regions such as deserts (Lourenço et al., 2012). Furthermore, if a fixative is to be used, we recommend a nontoxic fixing fluid.