Insect embryos develop inside eggs that contain food (yolk) needed for development. The embryo also needs oxygen for respiration. Insect eggs have areas permeable to air where oxygen can reach the embryo. In eggs that are laid in moist areas, water can cover the egg, block the respiratory channels and drown the embryo. Respiratory filaments are an adaptation to wet environments. Respiratory filaments are long tapered tubes that extend from the egg surface, tapering at the tip and contain an opening that allows gas exchange. In cases where the egg is submerged, respiratory filaments can extend above the water and reach the air.
Investigation* of the eggs laid by the Castor Butterfly, Ariadne merione revealed long respiratory filaments. Eggs are laid during monsoon season when torrential rains can cover vegetation. Respiratory filaments are unusual in butterflies that mostly lay eggs on plants that are not submerged. The respiratory filaments would allow castor butterflies to survive conditions that submerged the eggs.
*Asutosh Kumar Srivastava & Krishna Kumar. Ultrastructure of egg chorion of castor butterfly Ariadne merione (Crammer) (Lepidoptera: Nymphalidae). Zoologischer Anzeiger 263 (2016) 1–5