• Tue. Dec 5th, 2023

Global warming causes rapid decline in butterfly populations

ByGeorgina Hill

Nov 15, 2016

Butterflies: the ethereal beauties that enchant as they drift by on a warm summers day. Butterflies: the flapping beasts that charge at your face while you try to enjoy a picnic. Butterflies: which my dad used to call ‘flutterbies’, much to my childhood annoyance. Whatever you may feel about them, it is undeniable that butterflies are a staple of our colourful summer days. Unfortunately, across the UK, their numbers are in rapid decline. The UK Butterfly Monitoring Scheme has comprehensively tracked populations from over 1,8000 sites across the UK for 37 years.

Why this decline? Climate change. The root of all evil, the basis of many of our modern day problems. Seemingly, climate change is cited as the cause of all nasties, some even argue it being responsible for the rise of Donald Trump.

It is a common misconception that climate change will result in warmer weather all round. In reality, climate change will result in a change of weather patterns. We are already experiencing more extreme weather events across the globe. The 2015/2016 UK winter was no exception, with the warmest, wettest weather documented since records began in 1910.

Changing conditions will no doubt affect all species on earth. However, a butterfly’s life cycle is incredibly delicate. There are many stages involved as they go from egg to adult. One of these stages, metamorphosis, is possibly one of the greatest natural phenomena in the world – where stubby caterpillars are transformed into winged butterflies.

During winter butterflies are in the cocoon stage. Wrapped in their fibrous blankets, the tiny creatures are sensitive to environmental conditions. External conditions act as cues to dictate when they are to take on the next stage of life.

The team found that rainfall levels are particularly important: this aspect is often overlooked. As winters in the UK are expected to get wetter, butterfly populations are expected to be adversely affected. Still, unusually warm conditions were found to be the most damaging, with the population of over half of the species monitored decreasing compared to previous years.

The researchers suggest this may be because warm conditions are a cue for the end of winter and release of butterflies or their larvae. If an extreme warm weather event occurs, premature release means they are then killed off when weather conditions return to the seasonal norm. They also suggest populations could be lower because of increased incidence of disease, as most fungi and bacteria thrive in warmer conditions.

It is not all bad. The study shows that certain ‘warm-loving’ adults survived for longer into the winter. Therefore,  populations were higher than average. As the butterfly life cycle is so complex, the researchers are unsure of the impact that years with extreme warm summers and winters may have. Still, there is no doubt that climate change is having a detrimental effect on the worlds biodiversity as a whole.

Image: Barnes Dr Thomas G, U.S. Fish and Wildlife Service

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