The females of the brimstone butterfly (Gonepteryx rhamni) are greenish and not as intense a lemon-yellow colour as the males.
Brimstone butterfly: freeze, thaw, continue flying
The brimstone butterfly (Gonepteryx rhamni) is relatively widespread in Switzerland. Of the indigenous butterflies, it is the only one which hibernates as a winged, fully grown insect outdoors. All other butterflies hibernate during the winter as an egg/caterpillar/pupa or, for instance, in the case of the peacock butterfly, as a fully grown butterfly in frost-proof attics or in cellars. In contrast, the brimstone butterfly is unprotected in vegetation from late autumn onwards and exposed to the weather without any protection. So that its body does not freeze solid in temperatures below zero, it enriches it in a timely manner with an “anti-freeze agent” that consists predominantly of glycerine compounds. At the same time, the butterfly reduces its quantity of liquid and can thus withstand temperatures of down to minus 20° C without harm. When it has thawed again, life continues, even from as early as mild February days. Thanks to this unique lifecycle, brimstone butterflies live much longer than all other indigenous butterflies.