New Expedition Studying Impact of Climate Change on Orange Sulfur Butterflies

Because of human fossil fuel use, the world has gotten considerably warmer over the last 60 years, and even if we stopped all carbon dioxide emission today, this warming would continue for several more decades. Climate change has cascading effects on many aspects of the environment, from sea level to how early now melts to rainfall patterns, but there is one thing it can’t change: photoperiod (how much time it is light for each day). This is, in fact, a problem because daylength is used by many plants and animals to determine what time of year it is and thus predict the weather they will encounter. Photoperiod influences decisions ranging from when to produce leaves and flowers in plants to when to migrate and lay eggs for birds. But, now that any particular time of year is warmer without any change in photoperiod, animals and plants aren’t encountering the same conditions as they expected.

Colias eurytheme summer form

The Orange Sulfur Butterfly (Colias eurytheme) is one of the species encountering this problem. This butterfly is found throughout the US, and comes in two seasonal forms: in the summer, the dorsal (top) side of the wings is bright orange and the ventral (under) side is pale yellow, but in spring and fall, the dorsal side is yellow with a small orange patch, and the ventral side becomes darker. This darkening helps the butterflies warm themselves faster when bask in sunlight on cold days. These forms, however, are not determined by temperature but instead by the photoperiod. Thus, these butterflies are likely suffering from the mismatch between temperature and photoperiod created by climate change. What we want to know is if these butterflies have evolved to compensate for this mismatch, such as starting to produce the summer form at shorter photoperiods (earlier in the spring and later in the fall). To do so, we’re photographing thousands of these butterflies in museum collections from across the past 6+ decades.

Colias eurytheme spring/fall form

To use these specimens, however, we need to know when they were collected (among other details). This is where you and Notes from Nature come in. Date of collection is right there, recorded on the labels, but we need it digitized in order to work with it in our studies. You can help us access this data by transcribing it. By combining this label data with data we’re collecting about the butterfly’s wing patterns, we will be able to figure out what time of year the butterflies changed between color patterns in different years. We can then, in turn, determine if this color change has evolved in response to climate change, or if the butterflies are falling behind. Our images and the data you enter will also be contributed to LepNet, so future scientists can also make use of it.

This is the first of what will be multiple expeditions featuring these butterflies, this time using specimens from several collections, including the California Academy of Sciences, the Essig Museum at UC Davis, and the Smithsonian National Museum of Natural History. This will give us an initial dataset covering a variety of geographic areas. Thank you all for your help!

— Matthew Nielsen, University of North Carolina at Chapel Hill