Human development may be changing more than where pollinators live — it may also be changing when they are active.

University of Florida researchers at the Institute of Food and Agricultural Sciences (UF/IFAS) found that pollinator seasons shifted later in the year across some of the most human-modified landscapes in the eastern United States.

In fully human-modified landscapes, the eastern tiger swallowtail (Papilio glaucus) emerged approximately 33 days later and remained active about 23 days later into the year than in fully natural landscapes. [Photo by Corey T. Callaghan]

Using more than 80,000 observations submitted to iNaturalist, UF/IFAS researchers found that pollinator activity began about 22 days later and ended about 21 days later in the most human-modified landscapes compared with the least modified landscapes.

Researchers were surprised to learn that their overall season did not become longer, but instead the pollinator calendar shifted later.

The findings, published in Royal Society Open Science, provide one of the broadest looks at how human changes to natural areas may be altering the seasonal timing of pollinators across multiple insect groups, including butterflies, beetles and moths.

“We often think about cities as changing where species can live, but our results suggest it may also change when certain species are active,” said Marina Marquis, lead author and a former graduate student of Corey Callaghan, an assistant professor of global ecology at UF/IFAS Fort Lauderdale Research and Education Center.

Using data from a region stretching from central Alabama to central New York, the team compared the timing of pollinator seasonal activity across landscapes ranging from relatively natural to heavily modified by people. They measured human modification using factors such as development, agriculture and roads, while accounting for differences in temperature, precipitation, geography and species.

According to the study, the margined calligrapher, scientifically known as Toxomerus marginatus, did not shift its activity timing in relation to human modification. [Photo by Corey T. Callaghan]

“Cities, and those who live in cities, change vegetation, resources and many other features of the landscape at the same time,” said Callaghan. “If we are shifting the pollinator calendar, the big question is whether the plants and other species they interact with are shifting their calendars too. Ecological relationships depend on species being in the same place at the same time.”

The researchers also found that pollinators did not all respond in the same way. Findings suggest that individual species may respond differently depending on their biology, temperature sensitivity and relationships with plants.

Of the 52 species analyzed, 19 showed changes in at least one measure of seasonal activity. Some species began their activity earlier in more heavily modified areas, while others began later. Some species also had shorter or longer activity periods.

That variation could be important because pollinators depend on plants being available at the right time.

“For pollinators, timing matters,” said Marquis. “Bees, butterflies and other pollinators need flowers for food, and plants need pollinators to reproduce. If one changes its schedule and the other doesn’t, that relationship could be disrupted.”

The study also demonstrates how observations made by the public can help scientists investigate ecological changes across large areas, adding to a growing body of literature which demonstrates how iNaturalist is advancing ecology research.

“Cities are fascinating ecosystems because people are changing so many parts of the environment at once. Understanding how wildlife responds to those changes is becoming increasingly important as cities continue to grow,” said Callaghan. Platforms like iNaturalist give us a remarkable opportunity to study how nature is changing across species and entire regions — and to ask questions that simply weren’t possible at this scale before.”