1 G) from its spinnerets and attached it to the ant, preventing its escape ( Fig. During these tumbles, the spider used its hind legs to pull viscid silk ( Fig. The sudden initiation of attack was triggered either by contact ( n = 55) or when prey was at close range ( n = 5), possibly triggered by ants contacting silk lines. The first phase was an acrobatic strike during which the spider tumbled from its resting hunting position over the ant, irrespective of which direction the ant was approaching the spider from (ø = 306.17° ± 11.76, r = 0.101, n = 38, Rayleigh test, Z = 0.385, P = 0.68 Fig. A successful capture event involved two distinct phases. The analysis of the spider’s capture strategy started when the spider first moved from the sit-and-wait position. ( J) Image of the ant-slayer feeding on C. The spider holds the silk line with its right hind leg (white arrow in I) while the other end of the silk is attached to the ant. A line of viscid silk keeps the ant attached to the tree trunk (white arrow in H). ( H and I) Two stills from high-speed video recordings of the ant-slayer circling (clockwise) the ant ( C. ( G) SEM of the adhesive droplets on the viscid silk used during captures. ( Inset) Boxplot (5th to 95th percentile and median) of time taken from resting phase to top speed. ( F) Individual strike profiles (normalized t starts at 0 s) of different spiders during the tumble. ![]() ( E) An example speed profile of a spider during the capture sequence (unshaded area, strike phase white arrow, last resting position black arrow, maximum speed reached during strike). Successful attacks are shown in gray circles ( n = 38), and unsuccessful attacks are shown in black circles ( n = 5). ( D) Circular plot showing the direction and distance at which spiders attack the ants, with the center representing the spider position (0 = downward in the plane of the trunk). umbilicata-dorsal view of the Australian ant-slayer spider in a hunting position (photo credit: A.A.-A.). Each frame displays the average elapsed time and SEM in seconds between stages ( n = 22). ( B) Images 1–5 show corresponding frames from high-speed videos: ( 1) waiting flat position, ( 2) deploying viscid silk using hind legs, ( 3) directing silk toward the potential prey, ( 4) drop-off from trunk surface, and ( 5) resettling on the trunk. ( A) Images 1– 5 illustrate spider poses (prey not shown) at the five critical steps during the ant-slayers’ strike (illustrations: Zoe Wild). Hunting choreography of the Australian ant-slayer spider, E. However, the spider family Theridiidae likely diversified together with ants during the Cretaceous ( 5), resulting in relatively numerous myrmecophagous species and hunting strategies as seen in the genus Euryopis ( 6, 7).įig. Myrmecophagy is rare among most other taxa too, likely because ants have strong mandibles, the ability to spray formic acid, and strength in numbers ( 4). ![]() Ants are considered dangerous, and only ∼0.3% of known spider species feed on ants ( 3). However, the ants measured approximately twice the body length of the spiders, but with similar mass ( SI Appendix). Moreover, most predators feed on relatively smaller prey. Such extreme prey specialization is unusual, since predators typically feed on diverse prey types ( 2). We collected all prey items captured by spiders and found that the spiders almost exclusively captured ants (99.45%, n = 181/182), predominantly a single species, C. We surveyed multiple trees and found up to nine spiders actively hunting on a single tree. 1 G– I and Movies S1 and S2) to strike and immobilize their prey, the crepuscular banded sugar ants, Camponotus consobrinus, that also forage on Eucalyptus trees ( 1). Then, they use a continuous line of adhesive viscid silk ( Fig. As they settle, the spiders attach a silk line (dragline) to the tree trunk surface. The hunting sequence starts with a sit-and-wait period, followed by an acrobatic strike to the prey and successful capture by immobilizing the prey. With no capture web, they adopt a downward-facing position, flush against the trunk surface waiting for prey ( Fig. ![]() ![]() Euryopis umbilicata hide under the bark of Eucalyptus trees during the day and emerge at evening twilight.
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