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For this reason, they fail to capture local year-to-year variability in bee emergence, lending a false sense of uniformity to the start of the annual activity schedule for any given bee species, as well as exaggerating the duration of a species’ annual flight season. These are averages, however, the bulk of the specimens coming from the height of the nesting season, not its onset. This has been a popular means to assess responses of bee communities to global warming (refs in ). Records for abundantly collected species can also bracket the general calendar dates of seasonal activity, revealing latitudinal trends. The season(s) of each bee species’ period of regional adult activity can be compiled from collection dates on pinned museum specimens. Several short-term manipulative field studies with several solitary bees show that warmer nesting substrates also elicit earlier adult emergence. The most detailed records come from rare, long-term annual surveys of wildflower blooming schedules at a fixed location. As a consequence, some plant species are blooming earlier in recent decades. A warming climate is leading to hotter, longer summers, and milder, shorter winters, thereby advancing the regional onsets of spring and summer.

Other disruptive factors are intensifying, including urban sprawl and global warming. Some trends are long-running, such as the conversion of flower-rich prairies and other arable wildlands to agricultural monocultures. Native bee faunas and wildflower communities continue to suffer from diverse human impacts, particularly in temperate zones of the Northern Hemisphere.

Future monitoring studies can benefit from several simple methodological improvements.

Similar seasonal flexibilities in bee emergence and wildflower bloom schedules bodes well for bees and bloom to generally retain synchrony despite a warming climate. Emergence dates were relatable to thermal cues, such as degree day accumulation, soil temperature at nesting depth, and the first pulse of warm spring air temperatures. rubicundus emerged in close synchrony at multiple local aggregations, explicable if meteorological factors cue emergence. Calendar dates of earliest annual bee activity ranged across 25 to 45 days, approximating reported multi-decadal ranges for published wildflower bloom dates. This study reports direct observations spanning 12–24 years for annual variation in the earliest nesting or foraging activities by 1–4 populations of four native ground-nesting bees: Andrena fulva (Andrenidae), Halictus rubicundus (Halictidae), Habropoda laboriosa and Eucera ( Peponapis) pruinosa (Apidae). Resolving these competing scenarios requires evidence for bees’ natural plasticity in their annual emergence schedules. Nonetheless, some posit that global warming will decouple bee flight and host bloom periods, leading to pollination shortfalls and bee declines. Short-term field experiments with non-social bees showed that adult emergence is responsive to nest substrate temperatures. Global warming is extending growing seasons in temperate zones, yielding earlier wildflower blooms.