Western black widow spiders express state-dependent web-building strategies tailored to the presence of neighbours

Web-building spiders are territorial animals whose webs serve several purposes including foraging, reproduction and protection. Two factors are predicted to be of primary importance in determining a spider's web-building strategy: (1) current nutritional state (a function of prior feeding rate), which determines the net value of a web, and (2) the presence of co-occurring spiders with whom it may have to interact and partition resources. I conducted a laboratory experiment to test whether western black widow spiders, Latrodectus hesperus, express state-dependent web-building strategies that vary with the presence of conspecific or heterospecific (Tegenaria agrestis and T. duellica) spiders in a microhabitat. I maintained L. hesperus females on two different diets (high- versus low-food) and tested their web-building behaviour in the presence or absence of neighbours. When sharing a microhabitat with con- or heterospecific spiders, L. hesperus increased their web-building investment by producing higher-density webs containing more silk and by initiating web-building sooner. Web building was further influenced by nutritional state, such that well-fed spiders produced more silk and built denser webs than their poorly fed counterparts. Furthermore, microhabitat occupancy level and nutritional state showed a combined effect on the different components of web-building behaviour in L. hesperus. I discuss how this behavioural plasticity might optimize microhabitat settlement investments in the context of constraints on web-building activities imposed by nutritional state and cohabitation.