Ogre-Faced, Net-Casting Spiders Use Auditory Cues to Detect Airborne Prey

• Published in: Current biology 2020-12, Vol.30 (24), p.5033-5039.e3
• Main Authors: Stafstrom, Jay A., Menda, Gil, Nitzany, Eyal I., Hebets, Eileen A., Hoy, Ronald R.
• Format: Article
• Language: English
• Subjects: auditory detection; Deinopis spinosa, hearing; nocturnal; predatory behavior; sensory ecology; sensory systems
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2020.09.048

Prey capture behavior among spiders varies greatly from passive entrapment in webs to running down prey items on foot. Somewhere in the middle are the ogre-faced, net-casting spiders [1] (Deinopidae: Deinopis) that actively capture prey while being suspended within a frame web [2–5]. Using a net held between their front four legs, these spiders lunge downward to ensnare prey from off the ground beneath them. This “forward strike” is sensorially mediated by a massive pair of hypersensitive, night-vision eyes [5–7]. Deinopids can also intercept flying insects with a “backward strike,” a ballistically rapid, overhead back-twist, that seems not to rely on visual cues [4, 5, 8]. Past reports have hypothesized a role of acoustic detection in backward strike behavior [4, 5, 8]. Here, we report that the net-casting spider, Deinopis spinosa, can detect auditory stimuli from at least 2 m from the sound source, at or above 60 dB SPL, and that this acoustic sensitivity is sufficient to trigger backward strike behavior. We present neurophysiological recordings in response to acoustic stimulation, both from sound-sensitive areas in the brain and isolated forelegs, which demonstrate a broad range of auditory sensitivity (100–10,000 Hz). Moreover, we conducted behavioral assays of acoustic stimulation that confirm acoustic triggering of backward net-casting by frequencies in harmony with flight tones of known prey. However, acoustic stimulation using higher frequency sounds did not elicit predatory responses in D. spinosa. We hypothesize higher frequencies are emitted by avian predators and that detecting these auditory cues may aid in anti-predator behavior. [Display omitted] •D. spinosa are acoustically sensitive to a wide range of airborne tonal frequencies•Spiders respond to low-frequency tones as if capturing a flying insect•Spiders do not behaviorally respond to high-frequency tones in a foraging context•The metatarsal organ seems to play a role in acoustic detection Stafstrom et al. show that ogre-faced spiders are acoustically sensitive to a wide range of airborne tonal frequencies (100–10,000 Hz). By combining neurophysiological and behavioral experiments, spiders are shown to use low-frequency detection to capture flying prey. The behavioral relevance of high-frequency acoustic detection remains unknown.