Butterflies of
the Amazon and Andes
Common Tiger
Mechanitis polymnia
LINNAEUS,
1758
Family -
NYMPHALIDAE
subfamily - DANAINAE
Tribe - ITHOMIINI
subtribe - MECHANITINA
Mechanitis polymnia dorissides,
Rio Pindayo, Peru
Introduction
The Ithomiinae comprises of 376 known species, although it is
likely that at least another 30 will be discovered in the near
future. All are confined
to the neotropical region.
Ithomiines
are unpalatable to birds, and are consequently mimicked in
appearance by many other species. These include other unpalatable
species ( Müllerian mimics ), not only from the Ithomiinae but
also from several other butterfly families. There are also a large
number of edible species ( Batesian mimics ) which have evolved
similar patterns. Birds have the ability to memorise butterfly
patterns and so learn to avoid eating noxious species, but are
also fooled into ignoring similarly marked edible species.
Ithomiines are
characterised by having small eyes, slender abdomens and long
drooping antennae that lack distinct clubs. Males have a plume of
long androconial scales or "hair pencils" on the costa of their
hindwings. These are hidden from view when the butterflies are at
rest, but are displayed when the wings are held open during
courtship. Other Ithomiine characteristics include a very slow and
deep wing beat, and a preference for inhabiting the darkest
recesses of the forest understorey.
There are basically 2 types of Ithomiine. The first type are the
black and orange-banded "tigers", many of which are mimicked by
other species due to their unpalatability to birds. The second
type are the "glasswings", recognised by their transparent or
translucent wings, prominent veins, and orange wing margins. Many
genera contain examples of both of these types, and in some cases
an individual species may produce adults of both forms according
to location.
Most novices find the Ithomiinae very difficult to identify. Using
only the patterns to identify species is very unreliable because
there are so many similar species. Also many species produce a
variety of different colour forms according to locality and
season. The best approach therefore is to use the hindwing
venation and other anatomical features to identify the genus, and
to then look at the wing patterns to short-list the likely
species.
The
genus Mechanitis
contains 4 medium-sized species, all of which bear superficial similarities to
various members of other genera, including Melinaea,
Tithorea and Forbestra,
which have similar "tiger" patterning in black, orange and cream. All
these species ( and other smaller Ithomiines that have similar patterns ) are
toxic or unpalateable to birds. The shared pattern gives the butterflies an
"advantage in numbers" because insectivorous birds learn to avoid all "tiger"
species - tasting one such butterfly causes birds to vomit, and the experience
is enough to convince them to leave similar looking creatures alone.
The similarity of colour and pattern doesn't only fool the
birds - it also makes it difficult for human observers to distinguish the
species, so you need to learn how to
recognise particular unique characteristics. These include wing shape,
antennae length / colour, and the position and shape of particular spots in the
discal and apical parts of the wing.
Mechanitis
polymnia
is a very widespread species, distributed from Mexico to
Bolivia. There are 22 named subspecies, each
varying in colour and pattern. There is also considerable
variation between individuals at any given location e.g. some
examples seen at Rio Pindayo in June 2010 had a broad
creamy-yellow bar in the discal cell of the underside hindwing,
while in others it was vestigial.
The illustrated race
dorissides is restricted to eastern
Peru.
Mechanitis polymnia dorissides,
Rio Pindayo, Peru
Habitats
Mechanitis polymnia
is found in disturbed forest habitats including roadsides and adjacent farmland, at altitudes
between 0-1500m.
Lifecycle
The whitish barrel-shaped eggs are laid in batches of between 10-40 under the
leaves of Solanum and possibly other members of the
Solanaceae. The larvae are gregarious. When fully grown they are pale green
streaked with yellow, and have a series of tubercles projecting below the
spiracles. The chrysalis is golden with brown streaks on the wingpads and
abdomen.
Mechanitis polymnia dorissides,
Satipo, Peru
Adult behaviour
The butterfly is visible mainly in the early morning, and again in
late afternoon, at which time the females can
be found visiting Eupatorium flowers in forest clearings and along
riverbanks. Males in common with other Ithomiines, form "leks" to
which the females are attracted by pheromones. The pheromones are
disseminated by males from "hair pencils" - special androconial
scales located, in the case of Mechanitis,
on the costa of their upperside hindwings. These can be seen
protruding in the photograph of the ambushed example at the top of
the page.
In seasonal rainforests, where there
are pronounced wet and dry seasons,
Mechanitis gather to aestivate during the dry season at
the few remaining damp areas of the forest, typically in
gullies or along the beds of streams. Such places often have 100s of
Glasswing and Tiger-mimics Ithomiines in residence for up to 3
months towards the end of the dry season.
Mechanitis polymnia dorissides,
Satipo, Peru
|
