Monday, April 14, 2014

Butterfly Season


As the temperatures gradually rise we are seeing the awakening of butterflies.  We have been seeing the goatweed leafwings and mourning cloaks occasionally throughout the winter and now they are everywhere.  The adults survive the winter by hiding under lose bark, emerging occasionally to collect tree sap.  Lately we are seeing a few tiger and zebra swallowtails that have emerged from their cozy winter chrysalis.

Zebra Swallowtail - Chris Barnhart
The zebra swallowtails, Protographium_marcellus, are flying low and rapidly, never appearing to land.  I don't know where they get all their energy this time of year as they are nectar feeders.  The flowers in bloom are tiny wildflowers and tree blossoms such as serviceberry that lack the landing space for the butterfly's feet.  In spite of this there are many flirting pairs and at least one has been successful.

Early pawpaw flowers
As we passed a pawpaw grove, I noticed the first signs of flower buds starting to open.  This is always a dicey time for the future fruit as a sudden frost will turn them all black and there will be few pawpaw to collect in the late summer.  I have noticed that the flower buds appear over a period of several weeks and some late ones may emerge after a freeze.

Checking a number of trees I found a few leaf buds opening and then felt the sudden thrill of discovery.  There, on a tiny unfolding leaf, sat a glistening pale green egg of a zebra swallowtail.
 
A female zebra swallowtail very carefully lays an individual egg on the underside of a leaf.  It seems to know that its offspring don't play well together so it lays only one egg per leaf.  When the zebra caterpillar emerges, it eats the egg case for energy, and then may eat neighboring eggs if they are available.  Since the only likely species on a pawpaw are zebras, it doesn't pay to invest the energy in eggs that will not survive.  It is interesting to contemplate how this trait evolved.

Additional thoughts on April 14th:
Tonight as the front has moved through the temperature is forecast to drop to 25 degrees, likely to kill both the pawpaw flowers and the egg we have been following to record its turn to orange in several days.  While being the first bud or egg may give the organism a head start, it comes with a price.  The zebras are like to continue laying eggs.  Whether the pawpaw produces more flower buds is the next question and I am guessing that we won't have pawpaw fruit again this year. 

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