Butterflies of
the Andes
Oileus Owl butterfly
Caligo oileus
FELDER & FELDER, 1861
Family - NYMPHALIDAE
subfamily -
MORPHINAE
Tribe - BRASSOLINI
subtribe -
BRASSOLINA
introduction
|
habitats |
lifecycle |
adult behaviour
|
 |
|
Caligo
oileus umbratilis, San Pedro, Madre de Dios, Peru. |
Introduction
A few decades ago the Owl butterflies were considered to be members
of a now defunct family - the Brassolidae. Following the revisions of
Erlich ( 1958 ) and Ackery ( 1984 ), all of the butterflies with
only two pairs of walking legs were placed within the vast family
Nymphalidae. The Brassolidae became the Brassolinae - a subfamily,
and were then relegated further to become the Brassolini - a tribe
within the Morphinae.
The Morphinae includes an estimated
140-150 neotropical species, 93 of which are placed in the tribe
Brassolini. Of these, 73 are placed in the Brassolina - a
subtribe
which includes
Blepolenis,
Brassolis, Caligopsis,
Catoblepia, Dasyopthalma,
Dynastor, Mielkella,
Eryphanis, Mimoblepia,
Opoptera, Penetes, Opsiphanes,
Orobrassolis,
Selenophanes,
and
Caligo.
All are crepuscular or nocturnal in behaviour, although a few
species also fly by day in the darkest areas within their
habitats.
The 21 butterfly species
in the genus
Caligo
are known colloquially as Owl butterflies, due to the owl-like
false eyes, and the feathery appearance of the underside wings.
Various theories have been proposed to explain the presence of the
huge eyespots that adorn the underside hindwings of all species. The
butterflies rest for very long periods on tree trunks and can be quite
difficult to spot, but if accidentally disturbed by a bird they take flight, and if seen from below with wings fully open, could feasibly be
mistaken for an owl. When at rest however, only one side of the wings can be
seen at a time, and the appearance then is not owl-like. Another rather
far-fetched theory states that
the eyespot and surrounding dark areas are mimetic of a species of tree frog
that is said to rest on tree trunks where Owl butterflies are seen. It is however difficult to
imagine what possible advantage a butterfly might have in resembling a tree frog !
A far more rational likelihood is that the eyespot
functions as a decoy. The butterflies have a slow flapping flight, so a bird
could easily follow one to it's resting place.
Once settled however the mottled patterning
provides the
butterfly with superb camouflage against
the bark of a tree trunk, with only the eyespot
remaining prominent. Birds don't direct their beaks
aimlessly - they normally aim for the head or body of a
butterfly, but when the butterfly is well camouflaged they would aim instead at
the most obvious and prominent feature, which in this case is
the eyespot. I have seen many Owl butterflies which have had
large chunks pecked out of the hindwings, and this would tend to
support the decoy theory.
The underside markings of most
Caligo
species are prone to variation, which often causes confusion in
identification.
C. oileus
can be confused with oedipus, but the upperside forewings of the
former have broad suffused yellowish median bands, and the
upperside hindwings are flushed with deep blue. In
oedipus
the bands are much narrower and whiter, and the whole upperside is
flushed with greyish-blue.
Caligo oileus
occurs from Panama to Bolivia.
Habitats
This species inhabits cloudforest habitats at altitudes between about
800-1600m.
Lifecycle
Owl butterfly eggs are parasitised by tiny
Trichogrammatid wasps that ride from place to place on the hindwings of the
butterflies. They only leave the female's wings when she lays eggs, and then
return, to be transported to the next egg laying site. The eggs laid by any
individual female may be laid either singly, or in groups of twenty or more.
The larvae feed on
Heliconia
leaves ( Heliconiaceae ).
When fully grown they are a dull brown colour, marked with darker
longitudinal stripes, and have prominent forked tails, and a crown of horns
arising from their heads. The larvae are nocturnal, and rest during daylight
hours on dead leaves at the base of the foodplants, where they are superbly
camouflaged.
The
large stocky pupae are pale brown with darker streaks, and closely resemble bits
of dead foliage. They are formed hanging by the cremaster from woody stems or
amongst clumps of dead leaves.
Adult behaviour
The butterflies are usually
encountered as singletons, flying just before dusk along narrow
trails.
They are attracted to rotting plantains and other fruit on the
forest floor, and if disturbed fly in a seemingly very ungainly
fashion, with the flapping of their wings clearly audible.
Normally they fly only a few metres at a time, and settle clumsily
on foliage, often failing to maintain their grip, and being forced
to resettle elsewhere.
They continue flying through
the night, and are sometimes attracted into buildings by
artificial lighting. Just before dawn they seek out narrow tree
trunks, on which they roost during daylight hours at a height of
between 1-2 metres above ground level.
On particularly dull and damp
mornings they will continue flying, sometimes in quite open areas
along the edge of forest roads.
I once observed a Caligo nectaring at flowers in
mid-elevation rainforest in Ecuador, but they more usually feed at
fallen fruit on the forest floor, and can be baited with rotting
bananas or plantain.
The butterflies
are known to live for up to 3 months in captivity but it is not
known how long they live in the wild.
|
