Assassin bug uses aggressive mimicry to lure spider prey

Abstract

Assassin bugs (Stenolemus bituberus) hunt web-building spiders by invading the web and plucking the silk to generate vibrations that lure the resident spider into striking range. To test whether vibrations generated by bugs aggressively mimic the vibrations generated by insect prey, we compared the responses of spiders to bugs with how they responded to prey, courting male spiders and leaves falling into the web. We also analysed the associated vibrations. Similar spider orientation and approach behaviours were observed in response to vibrations from bugs and prey, whereas different behaviours were observed in response to vibrations from male spiders and leaves. Peak frequency and duration of vibrations generated by bugs were similar to those generated by prey and courting males. Further, vibrations from bugs had a temporal structure and amplitude that were similar to vibrations generated by leg and body movements of prey and distinctly different to vibrations from courting males or leaves, or prey beating their wings. To be an effective predator, bugs do not need to mimic the full range of prey vibrations. Instead bugs are general mimics of a subset of prey vibrations that fall within the range of vibrations classified by spiders as 'prey'.

Figure 1.

Responses of spiders to each vibration source. Significant differences are indicated by different letters (Fisher's exact tests). Black bar: orient, pause, copulatory position. Dark grey bar: direct approach. Grey bar: orient, pause, approach. Light grey bar: orient, no approach. White bar: no response.

Figure 2.

Peak frequency (back-transformed medians and inter-quartile ranges) of vibrations generated by hunting S. bituberus, struggling D. melanogaster and aphids, courting males, and leaves falling into the web. Significant differences are indicated by different letters (Tukey's tests).

Figure 3.

Amplitude (back-transformed medians and inter-quartile ranges) of (a) all vibrations, (b) the first vibration of each trial and (c) all vibrations except for the first generated, by hunting bugs, struggling vinegar flies and aphids, courting males and leaves falling into the web. Significant differences are indicated by different letters (Tukey's tests).

Figure 4.

Representative waveforms of vibrations generated by (a) bug plucking web, (b) leaf impacting web, (c) single aphid vibration making a small leg or body movement, (d) single vinegar fly vibration making a small leg or body movement, (e) aphid impacting web, (f) vinegar fly impacting web, (g) male spider making a small movement or step, (h) male spider ‘stridulating’ in web, (i) aphid wing beats in web and (j) vinegar fly wing beats in web. Note differences in time and amplitude scales.