Israel Journal of Ecology & Evolution, 2019 http://dx.doi.org/10.1163/22244662-20191057
Sit-and-wait prey: first field observations of scorpions preying on antlionsNeuroptera ( ) Nitzan Segeva,b,*, Efrat Gavish-Regevc and Oded Berger-Tala aMitrani Department of Desert Ecology, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Israel bDead-Sea & ‘Arava Science Center, Yotvata, Israel cThe Arachnid National Natural History Collection, the Hebrew University of Jerusalem, Jerusalem, Israel
Abstract Antlions (Neuroptera) are a group of sit-and-wait predator insects, with some species further specializing in digging conical pit-traps in the ground in order to catch prey. Studies on antlions’ predators are scarce with only few generalist predators known to feed on them. Here we report for the first time on field observations of antlions’ predation by three scorpion genera. We suggest that scorpions may be common predators of antlions, at least in the hyper-desert environment of southern Israel. The effects of predation risk on the behavior of sit-and-wait and particularly on trap-building predators received little attention in the literature. In light of our observations, we posit that predation risk must be taken into serious consideration in future research of antlions in particular, and sit-and-wait predators in general.
Keywords Antlion; scorpion; optimal foraging; trap-building; predation risk; ‘Avrona; Myrmeleontidae
Introduction 1987; Scharf and Dor, 2015). The most vulnerable period The foraging behavior of widely foraging predators (i.e., in TB predators’ life history occurs when it has to relocate predators that actively search for their prey) has been stud- its trap in order to find a better hunting site (Morse, 2013), ied extensively within the framework of optimal forag- since during the time spent on traveling to a new site, the ing theory. Classical foraging theory suggests that these TB predators are exposed to their own predators, as well predators should optimize the net rate of energy gain by as to parasites (Scharf et al., 2011). Among the triggers for attempting to obtain maximum energy in minimum time relocating the trap are extrinsic factors (e.g., competition, (Stephens and Krebs, 1986; Bell, 1991). More recent mod- disturbance) and intrinsic factors (e.g., body condition) els have implemented several additional constraints to this (Scharf and Ovadia, 2006; Parthasarathy and Somana- optimization rule, such as avoiding predation and the cost than, 2020). Widely-foraging predators may be special- of missed opportunities (Brown, 1988; Brown and Kotler, ized in identifying the trap as a source of food (Hauber, 2004). The comprehensively different foraging tactics of 1999; Shanas et al., 2017), therefore, the location and size sit-and-wait predators, and especially trap-builders (TB) of the trap may be influenced by predation risk. However, means that classical optimal foraging models may not very few studies investigate the effects of predation risk on readily predict their behavior, which might be the reason TB predators’ behavior (Scharf and Ovadia, 2006; Scharf for the fact that these predators receive significantly less et al., 2011). attention in the literature (Scharf et al., 2011). In contrast Antlions (Neuroptera: Myrmeleontidae) are a group of to widely foraging predators, the foraging effort among TB insects whose larval stages are sessile, sit-and-wait preda- predators is reflected mainly in the amount of energy in- tors. Some antlion species specialize in digging conical vested in the process of trap construction and maintenance pit-traps in dry loose soils in order to catch prey. Antlions (Uetz, 1992; Eltz, 1997). feed mostly on ants (70–100%, depending on antlion spe- There are various differences between the foraging be- cies) (Simon, 1988), as well as on other small arthropods haviors of widely-foraging and TB in addition to the most that fall into their traps (Lucas and Brockmann, 1981; obvious difference of how these predators obtain their Arnett and Gotelli, 2001; Alcalay et al., 2014). In addition prey. For instance, widely-foraging predators use different to catching prey, pit-traps can also provide shelter from the search tactics for different prey types or depending on the extreme desert temperatures in exposed soil (Marsh, 1987; spatial distribution of the prey (Greeff and Whiting, 2000; Gotelli, 1993; Mittler, 2007; Shanas et al., 2017) as well Fulton and Bellwood, 2002), while TB predators are gener- as provide shelter from predation (Griffiths, 1986; Lucas, alists, and as such they may not gain sufficient benefit from 1986; Scharf et al., 2011). However, Ruxton and Hansell adapting their foraging behavior to trap specific prey. In (2009) have suggested that antlions’ traps may also be a addition, by reducing their metabolic and respiration rates, disadvantage in regards to predation risk, since they may most TB predators can survive long periods of starvation be visually conspicuous to predators and parasitoids and when prey availability is low (Anderson, 1974; Matsura, help them locate the antlions.
*Corresponding author. E-mail: [email protected]
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Like with other TB predators, studies of antlion preda- was documented and identified to genus or species level. In tors are especially scarce: only few generalist predators are case of incidental observation outside of a survey plot or at known to feed on antlions, such as the carabid beetle (An- a different time from the survey transects, a GPS location thia sexmaculata (Fabricius, 1787)), a sit-and-pursue wolf was taken. In addition to our observations, we collected spider (Araneae: Lycosidae) (Loria Scharf Subach and more data from other observers in several arid places in Ovadia, 2008). Some birds are known to feed on antlions: southern Israel. Transliterated names of the localities fol- Arabian Babblers (Argya squamiceps (Cretzschmar, 1827)) low the “Israel Touring Map” (1:250,000) and “List of that were observed digging inside antlion pits, and feeding Settlements,” published by the Israel Survey, Ministry of on antlions (Shanas et al., 2017), Florida scrub-jays (Aph- Labor. elocoma coerulescens (Bosc, 1795)) are known to feed on antlions, furthermore, a single scrub-jay was observed feeding from a pit, and preferred large artificial pits in a Results set of foraging trials (Hauber, 1999), and Eurasian hoopoe Foraging observations (Upupa epops Linnaeus, 1758) (photographed observation in southern ‘Arava, Israel by Gil Koplovitz). Other possible Three scorpion species were observed foraging inside predators are several species of desert lizards, especially antlion pit-traps. Most of the observations ended with no underground dwelling skinks, that are specialized in move- active predation. Orthochirus scrobiculosus was observed ment and feeding inside the sand (Scharf et al., 2011; Sha- on four different occasions Table 1( ) performing active for- nas et al., 2017). Ants of the genus Pseudomyrmex (Lund, aging for antlion larvae by walking rapidly from one ant- 1831) play a double role – they can be either prey for the lion pit-trap to another without stopping for more than a antlions (if they fall into an active pit) or their predators (if few seconds inside the pit, and moving the sensory organs they find the larvae outside the pit) (Gatti and Farji-Brener, (pectines) rapidly. Orthochirus scrobiculosus hind abdo- 2002). Antlions are also exposed to conspecific predation. men (metasoma), usually held curled above the “back” Although all antlion species are solitary predators, they of- (mesosoma) with the stinger completely hidden (Levy and ten occur at high densities, owing to the uneven distribution Amitai, 1980), but when climbing outside the pit, some- of suitable microhabitats for trap construction (Matsura times, they were observed dragging the metasoma and et al., 2005). High densities increase aggressive interac- stinger on the ground behind them. Juveniles of Buthacus tions between antlions and promote cannibalism (Matsura yotvatensis, Buthus israelis and one mature O. scrobiculo- and Takano, 1989; Day and Zalucki, 2000; Alcalay et al., sus were observed ambushing for a few minutes, without 2014; Shanas et al., 2017). In addition to con-specific pre- any movement, inside an antlion’s pit, with their pincers dation, antlions are also exposed to asymmetrical intra- (pedipalp chelae) inserted in the sand at the bottom of the guild predation, with an advantage to the large specimen conical pit, where the antlion was hiding under the sand. between the different antlion species (Klokočovnik et al., When interrupted by us the scorpions climbed out of the 2020; Ovadia et al., 2020). pit (Fig. 1). Here we report for the first time on field observations of antlions’ predation by four scorpion species, Orthochi- Table 1. Observations assemblage of scorpions foraging for rus scrobiculosus (Grube, 1873); Buthus israelis Shulov antlion larvae (Myrmeleontidae) using different foraging meth- ods: 1Active foraging – walking on the ground inside and between and Amitai, 1959; Buthacus yotvatensis Levy, Amitai and 2 pits while moving the pectines, Ambush foraging – the scorpion Shulov, 1973; Buthacus sp. (Birula, 1908). We discuss the positioned inside the conical pit with the pedipalps towards the implications of our findings on sit-and-wait predators’ for- bottom, probably waiting to locate the antlion movement under aging theory. the surface (when threatened an antlion moves deeper into the sand). Scorpion Site Latitude Date Observer Methods species Longitude name Our study was conducted in the ‘Avrona Nature Reserve 1Orthochirus Og wadi 31.779996 03.09.2013 Yoram Zvik (also known as Evrona Nature Reserve). This reserve is a scrobiculosus 35.418317 hyper-arid habitat, located in the southern ‘Arava region, 1Orthochirus ‘Avrona 29.6758367 15.05.2017 Monitoring Israel. In May 2016, a five-year arachnid monitoring pro- scrobiculosus 35.0043567 team 1Orthochirus ‘Avrona 29.6824568 23.05.2017 Monitoring gram was launched as part of a multidisciplinary moni- scrobiculosus 34.9999232 team toring project of the Israel Nature and Parks Authorities 2Buthacus ‘Avrona 29.6823759 18.09.2017 Monitoring (INPA) and Israel’s National Nature Assessment Program yotvatensis 35.0001120 team (Ha’MAARAG). The monitoring scheme was initiated 2Buthacus ‘Avrona 29.6786153 25.05.2017 Monitoring following a major oil spill in the region. The Arachnid yotvatensis 35.0023747 team 2Buthus Mezad 30.985456 Spring Yoram Zvik monitoring area was divided into sixteen 10,000 sqm plots, israelis Yeroham 34.902402 2014 in which transects were assessed twice a year (May and 1Orthochirus ‘Avrona 29.6757304 15.05.2018 Monitoring August) during three consecutive “moonless” or “new scrobiculosus 35.0041668 team moon” nights. Transects were conducted by walking in 2Orthochirus Yeroham 30.599152 06.05.2019 Yoram Zvik parallel, straight lines inside the surveyed plot and using scrobiculosus park 34.535481 2Buthus Yeroham 30.599151 06.05.2019 Monitoring ultra-violet (UV) torches to detect scorpions, which fluo- israelis park 34.535480 team resce under UV light. As soon as a scorpion was spotted, it Downloaded from Brill.com11/18/2019 07:25:15AM via Tel Aviv University
Figure 1. Three scorpion species ambushing inside an antlion pit-trap: A) Orthochirus scrobiculosus under UV lightning; B) Buthacus yotvatensis; C) Buthus israelis.
Feeding observations Discussion We report here predation observations from different cli- We found that while predation on antlions by scorpions matic zones in Israel, mainly from hyper-arid areas where has never been reported before, it may be a common we concentrated our searching efforts, as well as arid areas, occurrence, at least in the hyper-desert environment of and a single observation in a semi-arid location. In seven southern Israel. This means that antlion larvae may be observations of active feeding by O. scrobiculosus, we an important factor in the oligotrophic desert system, not didn’t see the active prey capture moment, but we saw the only as predators, but also as a rich source of protein for scorpions in different prey-handling situations: on one oc- scorpions. casion the antlion larva was skewered on the stinger but on It is well established that predation risk can drastical- the other occasions it was held by the pincers (pedipalps), ly change the behavior of both prey and widely foraging or in the mouthparts (chelicerae). In all of these situations, mesopredator species, by altering their habitat choices, the scorpions were walking rapidly on the ground. Another vigilance behavior, foraging efficiency and activity times scorpion species, Buthacus sp., was observed walking with (Brown and Kotler, 2004). According to theory, pit con- Synclisis baetica (Rambur, 1842), a non-digging antlion struction is a product of the antlion’s optimal foraging strat- larva, in its mouth (Fig. 2). In another occasion, B. israelis egy (Scharf et al., 2011), with pit dimensions reliant upon was observed feeding on an antlion larva directly from the body size, soil characteristics (e.g., soil depth, sand par- pit. The prey in all of these cases was Neuroptera larvae, ticles size) and the internal state of the antlion (e.g., hunger mostly Myrmeleontidae, except for one observation of a level, perceived predation risk). No less important, finding scorpion preying on Ascalaphidae. Most observations oc- the ideal location for the pit-trap is crucial for the antlion’s curred during the night, except for one case of O. scrobicu- survival (Lomáscolo and Farji-Brener, 2001). Numerous losus feeding at noon in Elat’s Holland Park (Table 2). studies have dealt with the distribution and abundance
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Table 2. Observations of feeding by scorpions (Orthochirus scrobiculosus; Buthus Israelis; and Buthacus sp.) on antlion and owlfly larva (Myrmeleontidae1, Ascalaphidae2). Scorpion species Site Latitude Longitude Date Observer name 1Orthochirus scrobiculosus Haluza 31.091948 02.04.09 Amir Weinstein 34.671622 1Orthochirus scrobiculosus Samar dunes 29.8250933 05.04.16 Gil Koplovitz 35.0427369 1Orthochirus scrobiculosus ‘Avrona 29.6804966 23.05.17 Monitoring team 34.9980467 1Orthochirus scrobiculosus ‘Avrona 29.6701005 24.05.17 Monitoring team 34.9937684 1Orthochirus scrobiculosus Elat’s Holland Park 29.5729936 10.03.18 Gil Koplovitz 34.9601416 1Orthochirus scrobiculosus ‘Avrona 29.677422 24.04.18 Monitoring team 35.001718 1Buthus israelis Mezad Yeroham 30.985456 Spring 2014 Yoram Zvik 34.902402 2Orthochirus scrobiculosus Yeroham Park 30.993128 08.04.19 Yoram Zvik 34.886695 1Buthacus sp. Palmahim 31.923129 06.05.19 Itamar Ofer 34.727286
(Zyl, 1996; Gotelli, 1997; Napolitano, 1998) such as hunger level (Matsura, 1987; Scharf and Ovadia, 2006), prey avail- ability (Griffiths 1986) and prey arrival frequency (Caraco and Gillespie, 1986; Griffiths, 1986; Scharf et al., 2009). However, the risks involved with leaving the pit and walk- ing underneath the soil surface in order to build a new one (e.g., increased exposure to predation or cannibalism) have barely been studied. It is therefore unknown whether the behavioral consequences of predation risk on antlions are translated into life-history parameters (Scharf et al., 2011). According to theory, predation risk is positively correlated with the forager’s marginal cost while having little or no effect on its marginal benefit. Therefore the basic assump- tion is that the foraging investment of TB predators should decrease with increased predation risk (Scharf et al., 2011). Loria et al. (2008) found that pit-building antlions reduces pit construction activity when exposed to predators. Fur- thermore, the same study showed that antlions change their behavior depending on habitat structure: relocation and pit construction rates were lower in shallow sand than in deep sand since shallow sand probably does not provide suffi- cient shelter from predation compared to deep sand. Fol- lowing our observations, we posit that antlions are prob- ably exhibiting behavioral responses to predation risk in natural environment as well. We thereby believe that preda- tion risk must be taken into more serious consideration in future research of antlions in particular, and sit-and-wait Figure 2. Two scorpion species walking with an antlion larva in predators in general. their mouthparts (chelicerae). A) Orthochirus scrobiculosus feed- The current observations also add important informa- ing on Myrmeleon Linnaeus, 1767 sp. (photograph from Itay Tesler). tion on scorpion foraging in hyper-arid environments. Or- B) Buthacus sp. feeding on Synclisis baetica (photograph from Ita- mar Ofer). Some more cases of predation by O. scrobiculosus as thochirus scrobiculosus is characterized by a unique way well as predation by conspecifics, occurred inside artificial pitfall- of holding the metasoma curled above the back with hid- traps in ‘Avrona, but are not reported here. den stinger (Levy and Amitai, 1980) and it also has numer- ous shallow grooves on the metasoma, as the genus name of antlions’ pits as a function of local a-biotic conditions implies (from Latin, scrobiculus means “a little trench”.) (Marsh, 1987; Matsura et al., 2001) such as environmental Fet et al. (2003) suggested that these trenches could be (temperature, light) and physical soil parameters (Mittler, used as chemo-sensory organs, analogous to insect anten- 2007; Scharf et al., 2011), and of various biotic conditions nae. In our observations on O. scrobiculosus we saw that
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