Attending to detail by communal spider-eating spiders

Abstract

Communal predators may often need to make especially intricate foraging decisions, as a predator's success may depend on the actions of its neighbours. Here,we consider the decisions made by Portia africana, a jumping spider (Salticidae) that preys on other spiders, including Oecobius amboseli (Oecobiidae), a small prey spider that lives under small sheets of silk (nests) on the walls of buildings. P. africana juveniles settle near oecobiid nests and then ambush oecobiids as they leave or enter the nest. Two or more P. africana juveniles sometimes settle at the same nest and, when an oecobiid is captured, the P. africana juveniles may share the meal. We investigated the joining decisions made by naïve P. africana juveniles. Experiments were based on using lures (dead spiders positioned in lifelike posture) arranged in a series of 17 different scenes defined by the presence/absence of a nest, the lure types present and the configuration of the lures and the nest. Our findings imply that P. africana juveniles make remarkably precise predatory decisions, with the variables that matter including whether a nest is present, the identity of spiders inside and outside a nest and how spiders are positioned relative to each other and the nest.

Representation of different exact numbers of prey by a spider-eating predator

“…In other instances, a P. africana juvenile makes an ambushing attack when the oecobiid returns and begins to re-enter its nest [74]. Many factors, including whether other P. africana juveniles are already settled at the nest, influence P. africana's initial decision to settle at the nest [75]. The presence of conspecific individuals is relevant because, after one P. africana juvenile captures a single O. amboseli, other P. africana juveniles can feed on the same prey at the same time [74].…”

“…In experiments, P. africana juveniles were presented with lures made from dead oecobiids and dead conspecific individuals [68,75] and the sizes and arrangements of the dead prey and conspecific individuals were varied systematically. It was found that P. africana juveniles expressed their strongest predisposition to settle at occupied oecobiid nests when only a single other P. africana juvenile was present beside a nest occupied by an oecobiid.…”

The role of numerical competence in a specialized predatory strategy of an araneophagic spider

“…In typical sequences, two Portia settle alongside each other at an oecobiid's nest and when one Portia captures an oecobiid, it is joined by the other to feed alongside it. For the critical decision of whether to settle at an oecobiid nest, variables known to matter include whether a nest is present and occupied by an oecobiid instead of a similar-sized Portia, whether another Portia is already settled near the nest and is facing towards or away from the nest (Jackson and Nelson 2012).…”

The influence of camouflage and prey type on predatory decisions of jumping spider

“…Such dangerous prey can be approached differently when it is capable of attacking the spider or when its ability to defend itself is impaired . Some communal jumping spiders of the genus Portia make especially intricate predatory decisions based on the presence or absence of their prey nest, the identity of spiders inside and outside the nest and the position of these spiders relative to each other at the nest (Jackson & Nelson 2012). Making decisions requires from the spiders visual assessment of their environment and visual prey identification, often from a distance, and jumping spiders, due to their unique eyes, possess such abilities.…”

“…Principal eyes possess a unique structure (Land 1969a, b;Blest et al 1990) and provide spatial acuity unparalleled among any terrestrial invertebrates (Williams & McIntyre 1980;Harland & Jackson 2004). Some of the spiders can discriminate between objects spaced 0.12 mm apart from a distance of about 200 mm (Harland & Jackson 2004), which enables them to identify their prey based on a high degree of detail (Jackson & Nelson 2012;Nelson & Jackson 2012a, b). Jumping spiders can discern green, blue and ultraviolet (Land 1969a;Yamashita & Tateda 1976;Peaslee & Wilson 1989;Blest et al 1981) and were reported to discriminate between differently colored backgrounds (Nakamura & Yamashita 2000).…”