The Glasswing Butterfly, Greta oto, is distinguished by its nearly transparent wings, an adaptation that offers camouflage against predators. This species is commonly found across the wet forests and rainforests of Central and South America, from Mexico down through Panama and the Andes mountains. The diet of the Glasswing Butterfly differs dramatically between its larval and adult stages, with each demanding specific nutritional sources for growth, defense, and reproduction.
The Larval Diet
The caterpillar stage of the Glasswing Butterfly has a highly specialized diet, relying almost exclusively on host plants from the genus Cestrum. These plants belong to the poisonous nightshade family (Solanaceae). The larvae are classified as oligophagous, meaning they feed on a narrow range of plant species; using other plants can lead to slow development or death.
The caterpillars consume the leaves and absorb the plant’s toxic compounds, specifically alkaloids. This process, known as chemical sequestration, serves as a powerful defense mechanism. These sequestered toxins make the caterpillar unpalatable to predators, such as ants and birds, a protection advertised by the caterpillar’s bright coloration.
Adult Nectar Sources
Once adult, the Glasswing Butterfly’s primary energy source shifts entirely to nectar, consumed using its long, straw-like proboscis. Nectar is rich in sugars, providing the necessary fuel for the butterfly’s high energy demands. Adults are frequently observed feeding on flowering plants, particularly those in the genera Lantana and Cestrum.
They also seek out flowers from the Asteraceae and Boraginaceae families, which are widespread in their tropical habitats. As the butterflies move between flowers, they inadvertently transfer pollen, acting as pollinators. While nectar is the main energy source, it is nutritionally incomplete, lacking essential micronutrients the butterfly must acquire elsewhere.
The Importance of Mineral Supplementation
The adult Glasswing Butterfly engages in a supplementary feeding behavior known as “puddling” to address nutritional gaps left by a sugar-rich nectar diet. Puddling involves congregating on damp substrates like wet soil, mud puddles, or decaying fruit to sip moisture. This activity allows the butterfly to absorb essential minerals, such as sodium and nitrogen compounds like amino acids, which are scarce in flower nectar.
This behavior is particularly common among males, who require the absorbed minerals for reproductive success. The male Glasswing uses pyrrolizidine alkaloids, often obtained from plants in the Asteraceae family, to synthesize pheromones for attracting females during mating rituals.
Furthermore, the male transfers these acquired salts and minerals to the female during mating. This transfer is thought to improve the viability and health of the female’s eggs, ensuring the next generation is well-protected and robust.