Do pit-building predators prefer or avoid barriers? Wormlions' preference for walls depends on light conditions

Inon Scharf,Aziz Subach,Akiva Silberklang,Bar Avidov

doi:10.1038/s41598-020-67979-3

Abstract

Ambush site selection by sit-and-wait predators is a complex process, involving biotic and abiotic considerations, which greatly affect hunting success and costs. Wormlions are fly larvae that dig pit-traps in loose soil and hunt the arthropod prey falling into their pits. They are abundant in urban environments, found below buildings that provide cover, and many of their pits are dug adjacent to walls. We examined here under what conditions wormlions prefer to dig their pits next to walls. We analysed our dataset in two ways: frequency comparisons among the different treatment combinations and a simulation null model assuming random movement. While the frequency comparisons suggested that wormlions avoided the walls under some cases, the simulation null model suggested that a combination of shallow sand and strong light in the centre led to an attraction towards the walls, independent of the wormlions’ initial location. We suggest that wall attraction results from the certain amount of shade the walls provide. We also demonstrate that shallow sand and strong illumination are unfavourable microhabitats, either leading to more frequent movement or the digging of smaller pits. We locate our results within the broader context of sit-and-wait predators and of animals’ attraction to barriers.

Highlights

In contrast to widely-foraging predators, sit-and-wait predators do not search for prey
Whether the wormlion remained in its initial location relative to the wall or changed it depended on its original location (χ2 = 37.702, df = 3, n = 99, P < 0.001; Fig. 2a)
The tendency to move was mostly affected by sand depth and by the initial location (χ2 = 15.992, df = 3, P = 0.001; Fig. 2b)

Summary

Introduction

In contrast to widely-foraging predators, sit-and-wait predators do not search for prey. Similar to other sit-and-wait predators, TBPs balance their selection of ambush sites between the need to capture prey and the need to avoid unfavourable abiotic conditions, such as exposure to extreme temperatures or sites that restrict the ability to construct a functional trap[32,33]. For such reasons, TBPs often prefer specific natural or artificial structures. Such a preference for natural or artificial barriers has been explained by better thermal/humidity conditions next to the barrier, the reflection of light from a bright barrier that attracts potential prey, protection against rain, or help in the stabilization of the trap

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Conclusion