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Morpho Menelaus

Morpho menelaus is one of thirty species of butterfly in the Morphindae family. Its wingspan is approximately 12 cm, and its dorsal forewings and hindwings are a bright, iridescent blue edged with black, while the ventral surfaces are brown. Its iridescent wings are an area of interest in research because of its unique microstructure . Because of its unique blue color, the Morpho menelaus is considered a collector's item .

Range

This neotropical butterfly is found in places in Central and South America, including the Cerrado which is a vast tropical savanna in Brazil . Other locations include Mexico and Venezula. Ancestors of the Morpho menelaus butterfly may have been distributed in the Andean region.

Phylogeny

There is great variation among the various species of Morpho. Two categories of Morpho butterflies, achilles and hecuba, are distinct in flight behavior and vertical forest distribution. This habitat stratification between the two forest levels may have led to the diversification of the Morpho butterflies . Flight pattern behavior may also have led to changes in the wing shape to make it more suitable for gliding or flapping . Phylogenetic studies suggest these are indicative of ancestral qualities.

Morpho menelaus is part of the achilles sub-clade of Morpho. Other species in this sub-clade group include achilles, achillaena, peleides, granadensis, deidamia, laertes, polyphemus, catenarius, amothonte, didius, and godartii. There are no differences between males and females regarding forewing length, aspect ratio and wing centroid measurement which may be indicative of morphological homogeneity.  Despite the popularity of the Morpho butterfly, there is not a general consensus on the number of species or on how these species are defined. For instance, some consider M. amanthonte a subspecies of Morpho melanus, but this is not supported by morphology. Some older studies have identified 75 Morpho species, and newer studies recognize about 30 species. Despite the many species of the Morpho butterfly displayed in collections, they usually have mismatched or missing abdomens which make it difficult for research. Using combined studies of parsimony and Bayesian analyses, the Morpho melanus is associated with the M. helenor, M. sulkowskyi and M. amonthonte clades. The deviation of the Morpho melanus from the M. amonthonte is estimated to fall under the Pliocene era .

Behavior

Both sexes of the butterfly tend to inhabit the forest understory, but females are found near the tree tops when it is time to lay eggs. Both sexes have a slow and floppy flight pattern and feed on rotting fruit that has dropped to the ground. These butterflies tend to collectively emerge in the beginning and the end of the wet season in Cerrado. They tend to not appear in the middle of the wet season because the heavy rain can cause physical harm to their wings. This can be explained because of the Morpho menelaus may have been evolutionarily selected to synchronize with the availability of food determined by the climate. For protection from the rain, the Morpho menelaus prefers small and enclosed spaces.

Life Cycle

These social caterpillars feed on Erythroxylum, Dalbergia, and Fabaceae, and may prefer to feed on new leaves of host plants since these new leaves are easier and more profitable to eat. Conversely, the peak of the caterpillar is in the dry season, a climate that is unsuitable for most animal communities. These caterpillars will enter diapause and delay pupation in order to survive this period and the lack of water. As the dry season continues, the caterpillar population declines due to predation. One of the best predictors of butterfly occurrence is the number of zoochoric herbaceous species with ripe fruit. Adult emergence occurs primarily in the beginning of the wet season, when the climate and air humidity makes food resources plentiful and oviposition advantageous.

Coloration

The wings of Morpho menelaus are a prime example of iridescent blue coloration in the insect world. The bright and iridescent colors of other butterflies are typically caused by optical interference, but the iridescent blue color of butterflies in the Morphidae family results due to the microstructures of the wings. Using SEM, scanning electronic microscope, and spectroscopy, the structure of Morpho menelaus' wings can be understood in greater detail. 

Wing Structure

Each wing is covered in multi-layered scales, which are responsible for the coloration of the wings.  The wing colors vary with viewing angle, a phenomenon referred to as structural color. In the female, the dorsal side is more camouflaged while the male presents with a vibrant blue.  In the male, the outer layer of the cover scales are long and narrow (250 um x 50 um), 2 um apart, and parallel to the wing plane. The dimensions of the cover scales in other species of the Morphidae family vary greatly, but all are pigment-less and lowly iridescent. The inner layer, called ground scales, are pigmented, iridescent, do not overlap, and are responsible for the blue coloration. They consist of alternating layers of chitin and air, each having its own refractive indexes. Because the sizes of the structures are the same magnitude as the wavelength of light, the layers in the wings react strongly with visible light. The ground and cover scales have an observable “Christmas-tree” structure which is ultimately responsible for the diffraction pattern of the wings which results in the characteristic iridescence blue color.

The ground scales are covered by a set of longitudinal ridges, and within the ridges are layers of lamella. Because of the unique microstructure, there are distinct diffraction and interference effects like the brilliant blue of the males and a large diffraction angle. Within the ground scales are layers of lamella. The upper lamina is closely striated with a network of longitudinal ridges. Within this network themselves, there are individual lamellae (6-12) overlapping like shingles on a roof. The inter-spacing of the lamella layers is fairly consistent (around 80 nm), but there are variations in the thickness of each lamella. A network of netted trabeculae separates neighboring lamellae. In regards to the diffraction angle, the layer of lamellae with respect to the ridge is inclined at a slight angle (20 degrees). The increased number of lamellae is also correlated to the increase in amplitude of the reflected light. 

Research

Butterflies in the Morpho family are noteworthy for their multi-function characteristics, including being hydrophobic, lightweight, sturdy, thermally regulated, and bright blue iridescent. These unique characteristics originate from the photonic nanostructures in the ridges of the scales. Ongoing investigations into these unique characteristics inspire new ideas in engineering, biomedicine, and material sciences. 

Collections

Considered a collector's item, Morpho menelaus is unique because of its iridescent blue color and large wingspan. They are one of the most familiar and recognizable neotropical insects. Over the past century, there has been an accumulation of these butterflies in both private and museum collections. The monetary value associated with butterflies of the Morpho family perhaps drive its taxonomic understanding, which may explain the wide discrepancy of recognized number of species.