The execution of planned detours by spider-eating predators

Abstract

Many spiders from the salticid subfamily Spartaeinae specialize at preying on other spiders and they adopt complex strategies when targeting these dangerous prey. We tested 15 of these spider-eating spartaeine species for the capacity to plan detours ahead of time. Each trial began with the test subject on top of a tower from which it could view two boxes: one containing prey and the other not containing prey. The distance between the tower and the boxes was too far to reach by leaping and the tower sat on a platform surrounded by water. As the species studied are known to avoid water, the only way they could reach the prey without getting wet was by taking one of two circuitous walkways from the platform: one leading to the prey ('correct') and one not leading to the prey ('incorrect'). After leaving the tower, the test subject could not see the prey and sometimes it had to walk past the incorrect walkway before reaching the correct walkway. Yet all 15 species chose the correct walkway significantly more often than the incorrect walkway. We propose that these findings exemplify genuine cognition based on representation.

Keywords: Spartaeinae; cognition; detouring; jumping spiders; planning; representation.

Fig. 1

Apparatus used in detour-choice experiments. Not drawn to scale. (A) Pan (filled with water) and Walls (S1, S2, S3, S4) not shown. Beginning of trial: Lid (not shown) covering Pit was removed and test spider walked out of Pit and on to top of Tower. Two Boxes (Box A and Box B) positioned on Support Poles above water. Prey Holder (with four lures made from Oecobius amboseli) in one Box and Control Holder (with four green-leaf pieces) in other Box. Box with Prey Holder determined at random. After test spider leaves top of Tower, Holders moved out of Boxes and hidden behind S1. To complete successful trial, test spider chooses A1 or B1 after leaving Tower and walking across Platform. To reach Box A or Box B, test spider walks along Walkway A or Walkway B until reaching Intersection A5 or Intersection B5, respectively. Walkways held above water by Support Poles. Test spider could opt out of taking detour by walking across Platform to reach S3. (B) and (C) Stand for supporting Pins and Holders positioned behind S1. Button (not shown) pressed on lever-operated device to move Holders up (7 mm) and down (7 mm) in unison while test spider on Tower. (B) Pins and Holders in lowered position. (C) Pins and Holders in raised position. (D) Holders positioned inside Box A and Box B (Boxes shown are transparent for view of positioning of Holders). Boxes were open at back. Pins in Styrofoam keep Holders in place. Pins go through openings of S1 to Stand out of view behind S1.

Fig. 2

Total number of test spiders (pooled data) that made a correct or incorrect choice after approaching a Walkway directly or indirectly (see text for definitions).

Fig. 3

Score (i.e., how far individuals progressed along Walkway before trial ended) for each species tested. Score (1–4) indicates Intersection reached before trial ended (see Methods for details). For example, score 1: spider reached Intersection A1 when Walkway A was correct or B1 when Walkway B was correct. All spiders that reached Intersection 4 continued to Intersection 5. Boxes show medians plus upper and lower quartiles. Whiskers show minimum and maximum values. Sample size (number of test spiders that made a correct choice of Walkway) indicated for each species.

Fig. 4

For all individuals tested (pooled data), progress along Walkway before trial ended. Each spider was given a score (1–4) that corresponded to Intersection reached before trial ended (see Methods for details). For example, Score 1: test spider reached Intersection A1 or B1 before trial ended. All spiders that reached Intersection 4 continued to Intersection 5. Percentages calculated separately for test spiders that chose correct Walkway and individuals that chose incorrect Walkway. Number of test spiders that chose correct Walkway and number of test spiders that chose incorrect Walkway shown above bars.