The Menelaus blue morpho (Morpho menelaus) is one of thirty species of butterfly in the subfamily Morphinae. Its wingspan is approximately 12 cm (4.7"), 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 their unique microstructure. Due to its characteristic blue color, Morpho menelaus is considered valuable among collectors and was widely hunted in the 20th century.
This neotropical butterfly is found in Central and South America, including the Cerrado which is a vast tropical savanna in Brazil. Other locations include Mexico and Venezuela. Ancestors of the Morpho menelaus butterfly may have been distributed in the Andean regions. Morpho menelaus is one of the six species of Morpho in Costa Rica. The genus of Morpho is present in regions beginning in Mexico and throughout South America, except Chile. Moreover, the Morpho menelaus struggle to survive in the northern Pacific area of Costa Rica since they can’t tolerate such dry conditions. They also need habitats in old growth forests with proper differentiation between the understories and canopies (Murillo-Hiller & Canet, 2018).
There is great variation among the various species of Morpho. Two groups 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.
Females inhabit the forest understory and perch on tree stumps, but 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. Males tend to fly in open clearings or high in the canopy. These butterflies collectively emerge in the beginning and the end of the wet season in Cerrado. They do not appear in the middle of the wet season because the heavy rain can cause physical harm to their wings. Their emergence depends on the availability of food which is dependent on climate. For protection from the rain, Morpho menelaus prefers small and enclosed spaces.
The egg of the Morpho menelaus butterfly is typically small, round, and somewhat flattened. They are usually pale green or whitish in color, sometimes with a slightly metallic sheen, but not as vibrant as the adult butterfly's iridescent blue wings, and shaped like dew drops. The female laid around 12 eggs in cluster of 5 or 6 eggs on the undersides of the leaves. The eggs are laid so that the caterpillars may feed as soon as they hatch.
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 nutritious to eat. The caterpillars are red-brown in color with bright green spots. They are covered with bristles that release an irritant upon contact. 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 or suspend development and can delay pupation in order to survive this harsh period and the lack of water. As the dry season continues, the caterpillar population declines due to predation.
One of the best seasonal predictors of adult butterfly occurrence is the ripening of zoochorous 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. The butterfly spends 3 to 4 weeks as an adult, and the entire life cycle is about 115 days. Adults fly along rivers, or anywhere that open land has been revealed.
Eyespots on wings are visual anti-predatory adaptations that have evolved in many species within Lepidoptera. The eyespots are usually dark circles surrounded by a brighter outer layer. The 'pupil' of the eye has a sparkle that mimics the natural reflection of the cornea. These eyes are thought to deflect a predator's attack away from more vital organs and toward that spot on the wings. Bigger eyespots have also been shown to deter predators from attacking completely. Menelaus specifically has an eyespot that is 6.8 mm in diameter on its ventral wings that it uses to help avoid predation.
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 family Morphidae results from the microstructures of the wings. Scientists use SEM, scanning electronic microscope, and spectroscopy, to understand the wings in greater detail.
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 μm × 50 μm), 2 μm apart, and parallel to the wing plane. The dimensions of the cover scales in other species of the subfamily Morphinae 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. The wings of the genus Morpho are noteworthy for their diversity of function, 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. There has been increasing interest in the bioengineering community into understanding the structural components of the wing which can have potential applications in creating structural-color devices and selective gas-sensors.
