Abstract
Aquatic insects live through some stages of their life cycle in the water. They have developed various types of attachment systems to resist rapid water flow. Combinations of different attachment devices can offer aquatic insects advantages in underwater adhesion on substrates with different surface properties. In this study, the larvae of Dobsonfly (Neochauliodes sinensis) and Blepharicera sp. were investigated to understand the relationship between micro-/nano-structure and attachment mechanisms. The hierarchical structures of insect adhesive surface were characterized by optical microscopy and scanning electron microscopy. Centrifugal measurements were also conducted to measure the critical rotational velocities that insects can adhere to different substrates. Attachment structures and mechanisms for different aquatic insects are discussed and compared in this research. Suckers require smooth substrate surface for developing negative pressure under the sucker cup while claws, hooks or frictional pads need irregularities to attach to the rough surfaces by interlocking or frictional force. Furthermore, the functions of microstructures including wrinkle surface, inward setae, outer fibers and nick, observed on the sucker of the larva of Blepharicera sp. were also explored. It has been proved that capillarity has no or minor contribution to the underwater adhesion of sucker. Critical rotational velocity of the larva of Blepharicera sp. reach ~1600 rpm which is over 5 times than that of the larva of dobsonfly measured on Teflon substrate. The unique microstructure and adhesion capability of such sucker could shed light on the design and synthesis of novel bio-inspired devices for underwater adhesion.