Flood Pain For Butterflies?


The wettest winter on record has brought flooding misery to many homeowners and left large swathes of southern England under water. 

A combination of storms, heavy rainfall, flooding, strong winds and mild weather has made the winter of 2014 memorable for all the wrong reasons. 

Small mammals, insects and birds have all been affected by the flooding, but just how have our butterflies fared? 

Rather than the flooding, Butterfly Conservation is most concerned about how mild this winter has been with a distinct lack of frosts and cold weather. Butterflies are adapted to cold winters. Death by freezing isn’t so much related to low temperature itself as it is the result of ice crystals forming in the body. Rapid formation and expansion of ice crystals cause cells to burst, resulting in organ and gut damage. But butterflies get around this by being freeze-tolerant – they actually survive the formation of ice crystals in their body by producing ice nucleating proteins that “control” the freezing process. 

The mild weather increases activity levels of pathogens making the overwintering immature stages (caterpillars, eggs and pupae) of butterflies increasingly susceptible to diseases. Wet weather probably plays a role here too. Mild weather also raises metabolism, which means there is a danger of them using far more energy than normal and ‘running out of fuel’ before they complete development. 

A handful of butterflies like the Brimstone and Small Tortoiseshell overwinter as adults hiding away in trees, bushes and buildings. Warm winters interrupt the dormancy of overwintering adult butterflies making them more vulnerable to predation by bats and birds. They will also be using up their energy reserves flying around looking for nectar when there are few if any plants flowering. 

We are a little less concerned about flooding, because a lot of the flooding has come and gone quickly or is along flood plains where either any remaining good quality habitats will be naturally waterlogged and used to flooding or  don’t support too many butterflies if they have been highly modified by agricultural intensification. 

But, we are concerned by the extremity of the rainfall this year – the wettest for 250 years or so. It’s important to remember that very dry conditions can be just as damaging - some rare butterflies have never fully recovered from the extreme drought we had in 1976. 

We simply can’t be sure of the effects in terms of extreme rainfall and it is vital our monitoring continues this summer to evaluate any impacts.

Dr Tom Brereton
Butterfly Conservation Head of Monitoring