Spring has sprung decidedly early this year, with children where I live on the East Coast already wearing shorts to school. But the early spring is bad news for butterflies. Carol Boggs, a biologist at Stanford University, and other researchers have traced a decline in the population of the Mormon Fritillary butterfly (Speyeria mormonia) to snowmelt caused by climate change in the Colorado Rocky Mountains. The early snowmelt has led to a decrease in the number of flowers, which has in turn decreased how much nectar is available for butterflies to feed on.
The researchers’ findings have been published in the journal Ecology Letters.
In their first summer, butterflies lay eggs and then die; laboratory experiments have determined that the amount of nectar a butterfly consumes affects the numbers of eggs she lays. The caterpillars from the eggs do not eat during the winter and become adults the summer after. Science Daily outlines the chain of events, sparked by climate change, that have led to a decline in the butterfly population.
Early snowmelt in the first year leads to lower availability of the butterfly’s preferred flower species, a result of newly developing plants being exposed to early-season frosts that kill flower buds.
The ecologists showed that reduced flower–and therefore nectar–availability per butterfly adversely affected butterfly population growth rate.
Early snowmelt in the second year of the butterfly life cycle worsened the effect, probably through direct killing of caterpillars during early-season frosts.
The combined effects of snowmelt in the two consecutive years explained more than four-fifths of the variation in population growth rate.
Boggs has indeed observed that the upcoming summer will be a difficult one for butterflies “because the very low snowpack in the mountains this winter makes it likely that there will be significant frost damage.” David Inouye, a biologist at the University of Maryland and a co-author of the study, points out that there are “broader effects of weather on an ever-changing Earth.”
Indeed, the conditions wrought by climate change have taken a toll in other ways on the insect population. The oddly mild winter on the East Coast is likely to “wreak havoc” on the bee population in New Jersey. Bees are usually semi-dormant in the winter but, due to mild temperatures, they have remained active in the past few months and eaten through their reserve honey stores, which are meant to last until spring. Without enough food, their numbers are likely to decline.
I’m not sure about you, but I really wish the winter had been colder. As much as some may appreciate wearing summery clothes in early March, wouldn’t you rather bundling up for the sake of the butterflies and bees?
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Photo by Bill Bouton