This afternoon we took the opportunity afforded by an open house at our home to visit Eagle Rock Reservation in West Orange. It was a beautiful day to be out of doors with clear blue skies and temperatures in the upper 50s. We probably walked a little over two miles on the yellow-blazed Lenape trail, along the section that runs roughly north and south near the crest of the ridge.
We heard numerous birds, including a nuthatch, a flicker–which we also saw–and a tufted titmouse among others.
On the return trip to the car I was surprised to see a butterfly. It seemed too early to see any butterflies, and yet there it was. It rested long enough in one spot on the ground that I was able to take several photographs. A few yards further on we actually saw a second butterfly, smaller and red-orange in color, that would not alight long enough in any one spot for me to photograph it.
This evening I searched Google for butterfly identification resources hoping to be able to identify the butterfly that I photographed. It is a Mourning Cloak butterfly (Nymphalis antiopa). The Mourning Cloak is the state butterfly of Montana, which gives some indication of the kind of climate the butterfly will tolerate. Unlike Monarchs, for example, which are well known for the distances they migrate, Mourning Cloaks overwinter in one location and do not migrate. This means that they are among the earliest butterflies to be seen in the spring.
It occurs to me that an insect that overwinters in a cold locale must be able to tolerate being frozen. How is that possible? How are insects different from mammals in that regard? Some insects are freeze-tolerant, which means that the water in their cells actually freezes, and some are freeze-susceptible and must somehow produce sufficient antifreeze compounds to prevent the fluid in their cells from freezing. The antifreeze compound most commonly produced by freeze-susceptible insects is ethylene glycol, the same compound that is used as an antifreeze agent for automobile cooling systems. (Source: http://www.colostate.edu/Depts/CoopExt/4DMG/Pests/winter.htm viewed 6th April 2014)