Sit-And-Wait Prey: First Field Observations of Scorpions Preying on Antlions (Neuroptera)

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 antlions (Neuroptera) 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] Downloaded from Brill.com11/18/2019 07:25:15AM © Koninklijke Brill NV, Leiden 2019 via Tel Aviv University <UN> 2 N. Segev et al. 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

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