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.