Multimodal and multifunctional signaling? – web reduction courtship behavior in a North American population of the false black widow spider

Males of widow spiders courting on the web of females engage in web
reduction behavior which entails excising a section of the web, bundling
it up, and wrapping it with their silk. Males of the false black widow
spider, Steatoda grossa , in European populations also produce
stridulatory courtship sound which has not yet been studied in their
invaded North American range. Working with a North American population of
S. grossa , we tested the hypotheses that (1) web reduction by males
renders webs less attractive to rival males; (2) deposition of silk by
courting males has an inter-sexual (male-female) signal function that
enhances their likelihood of copulation; and (3) stridulatory sound is a
courtship signal of males. Testing anemotactic attraction of males in
Y-tube olfactometer experiments revealed that reduced webs (indicative of
a mated female) and intact webs (indicative of a virgin female) were
equally attractive to males. Recording courtship behavior of males with
either functional (silk-releasing) spinnerets or spinnerets experimentally
occluded on the web of virgin females showed that males with functional
spinnerets were more likely to copulate with the female they courted.
Although males possess the stridulatory apparatus to produce courtship
sound, they did not stridulate when courting or copulating on the web of
females. Our data support the conclusion that web reduction behavior of S.
grossa males in their invaded North American range has no long-range
effect on mate seeking males. Instead, web reduction behavior has an
inter-sexual signaling function that seems to be linked to functional
spinnerets of the courting male. The signal produced by a male likely
entails a volatile silk-borne pheromone, but may also embody a gauge of
his endurance (the amount of time he engages in web reduction causing web
vibrations).