Urban heat island conditions experienced by the Western black widow spider (Latrodectus hesperus): extreme heat slows development but results in behavioral accommodations

Herein lies data on urban h eat island conditions for black widow spiders across the CAP study area. It also includes data on the development speed and behavioral responses of spiders reared in the lab at these UHI temperatures. The urban heat island (UHI) effect describes the capture of heat by built structures (e.g. asphalt), resulting in elevated urban temperatures. The UHI is a well-studied phenomenon, but only a handful of studies have investigated trait-based shifts resulting from the UHI, and even fewer have attempted to quantify the magnitude of the UHI experienced at the microclimate scale. Here, using a common urban exploiter, the Western black widow spider (Latrodectus hesperus), we show that the UHI experienced by spiders in July in their urban Phoenix, AZ refuges is 6 degrees C hotter (33 degrees C) than conditions in the refuges of spiders from Sonoran Desert habitat outside of Phoenix-area development (27 degrees C). We then use this field microclimate UHI estimate to compare the development speed, mass gain and mortality of replicate siblings from 36 urban lineages reared at temperatures that reflect urban and desert habitats. We show that extreme heat is slowing the growth of spiderlings and increasing mortality. In contrast, we show that development of male spiders to their penultimate moult is accelerated by 2 weeks. Lastly, in terms of behavioral shifts, UHI temperatures caused late-stage juvenile male spiders to heighten their foraging voracity and late-stage juvenile female spiders to curtail their web-building behavior.