Once in a Blue Moon
By James Maxwell Overton
Some people would say it is not often that the label
"romantic" can be attached to New Zealanders, but their name for one of our
common garden butterflies shows a certain poetic spirit. The butterfly is the one we call
the common eggfly (Hypolimnas bolina ). It is an infrequent visitor to the 'Shaky Isles',
and, not having large numbers of beautiful butterflies of
their own, has been given the lovely name of "Blue Moon".
The name is appropriate, both for its rarity (in nearly 30 years in New
Zealand I only glimpsed one once), and for the beautiful markings on the wings of the
male. Both front and hind wings are a velvety black with a large round white
"moon" dusted with an iridescent purplish blue. In Australia it is a common
butterfly, being found throughout the east and north of the continent.
If you disturb a male eggfly sunning itself in your garden, you will
find that though it may fly away, it soon returns to its original position. The butterfly
is in fact guarding a small territory, and will defend it against other males. When a
strange male eggfly wanders too close, the resident male will fly at it. Each butterfly
will then circle, trying to keep a position above the other, often spiralling upward into
the sky. Almost always it is the resident male that wins out and returns to its perch.
Sometimes the males get so enthusiastic that they will fly out and challenge anything
flying past, even birds!
While the male eggflies all look much the same, the females are very
variable. Typically, the front wings are a dark brown or black with white spots dusted
with blue at the leading edge. At the lower edge of the same wing is a large orange patch.
The hindwing has a large white area with a dusting of blue around the margins. This white
area sometimes is bordered in orange rather than blue, and the size of the white area
varies a lot. Some females around Townsville show even greater variability, losing the
orange patch entirely, or expanding it to cover most of the wings. Underneath, both sexes
are brown with white spots and a broad white stripe.
The eggs are pale yellowish-green and are laid in small groups on
low-growing weedy plants found in shady or swampy areas. The plants most often used are
joyweed (Alternanthera denticulata), and sida-retusa (Sida rhombifolia). Mature larvae are
dark brown or black with branched spines and a thin yellow side stripe. They will only
feed at night, spending the day concealed at some distance from the food plant. The pupa
is brown, mottled with darker brown or black.
The adults will feed readily from flowers in the garden, and love
fiddlewood and the strawberry tree, as well as such popular butterfly flowers as Lantana
and Pentas. We can count ourselves luckier than New Zealanders to have such a beautiful
butterfly as a regular visitor to our gardens.
Copyright © 1998,1999 JM Overton
