Trait data
We collected trait information from literature and web sources for the 284 included insect species. We focused on traits thought to be relevant to insect phenology, including: 1) voltinism, 2) development type, 3) habitat of immature life stage, 4) diapause stage, and 5) larval diet. We also estimated a categorical trait for the season of adult emergence by calculating the mean emergence for each species. Species that on average emerge as adults prior to the 126th day of the year (DOY) were categorized as spring species, those between the 126th and 176th (~ end of June) DOY were categorized as summer species, and the remaining insects were categorized as fall species. Voltinism (broods per year) was categorized as either obligate univoltine, or not obligate univoltine (including species that are only univoltine in part of their range and semi-, parti-, and merovoltine species). Development type was categorized as either hemimetabolous or holometabolous. Habitat of immature life stage was categorized as above ground, freshwater, or underground. Diapause stage was categorized as egg, larva, pupa, adult, none, or migratory. The larval diet was categorized as carnivorous, detritivorous, or herbivorous.
Many of the species that passed initial filters for numbers of observations were missing trait data and were excluded from further analyses (Figure 1). We also removed species that do not diapause or are migratory, as these species likely have different physiological responses to temperature and urbanization than the other species. Additionally, eusocial insects were removed, because many can thermoregulate in unique ways (Heinrich, 1972; Jones and Oldroyd, 2006; Menzel and Feldmeyer, 2021). Finally, we removed species that had less than 5 unique year-by-grid cell combinations. After filtering our dataset to match these requirements, we were left with 2,643 estimates of emergence, termination, and duration from 101 species across 412 unique grid cells (Figure 2).