Island environments can be a tough world for the species that call them home. Even though some islands are exposed to extreme winds and rain, especially in the event of climatic events such as tropical cyclones, animals and plants persist. One adaptation to these environmental pressures is that the tiniest island dwelling creatures, insects, are more often flightless, to protect themselves from being carried away by unexpected winds. But how do they cling on to stay put when the weather turns extreme? Knowing that flightless weevils live high up in the windy forest canopy of Orchid Island, Taiwan, Lu-Yi Wang from the University of Melbourne, Australia, and an international team of colleagues decided to investigate how sticky the wind-beaten weevils’ feet are, to understand how they manage to stay put with the constant threat to being blown away.

To test the ‘stickiness’, or adhesion, of these insects’ feet, the team collected live weevils from the island and put them on a disc that was spun fast, to force them to cling on. By increasing the spinning speed and recording when the bugs fell off, the team could calculate how well each bug stuck to the surface with the sticky pads on their feet. In addition, the team changed the roughness of the disc surface to see how the insects’ ability to cling on changed as the surface became rougher. Lastly, knowing that the weevils’ feet come equipped with a claw for hanging on, the team also tested how this grappling hook contributed to the insects’ ability to cling on by repeating the disc-spinning experiment after snipping off their claws. The team then compared how tightly the Orchid Island weevils hung on with and without their claws, as well as the sticking power of these island weevils and those that live in less windy landlocked locations.

Wang and colleagues found that the Orchid Island weevils show much stronger attachment forces than previously measured for non-island-dwelling insects. On rough surfaces, the island weevils’ attachment forces were 12% higher than those recorded for other insects. The weevils also had a 7% higher safety margin, meaning that their maximum attachment force exceeds a higher multiple of their body weight compared with other insects. On slick glass surfaces, the weevils held on 14 times more strongly than bugs that came from less windy locations. When the team compared how well the island dwellers hung on with and without their claws, the clawless weevils that only had their sticky pads to cling on with held on as tightly as the clawed weevils, so the insects’ claws did not contribute to their ability to hang on tight in the wind. And when the team took a detailed look at the sticky pads on the insects’ feet using an electron microscope, they found that the weevils have long but soft hairs on their footpads, which can mould snuggly to any surface, creating a large contact area to hold the insect in place through molecular forces.

This study shows that these endangered and protected Orchid Island weevils show impressive attachment ability, which is an important adaptation to island life. Stronger adhesion not only prevents them from being carried away by strong winds but also avoids them falling prey to other small bugs such as ants. The ability of these creatures to attach strongly to a surface is caused by the structure of the sticky pads on their feet, as well as the softness of the base and tips of the adhesive hairs that cover the sticky pad surface, allowing the weevils’ toes to make intimate contact with any surface, from the roughest to the smoothest. These insights might help researchers understand how species adapt to extreme weather, which might occur more often as a result of climate change.

Wang
,
L.
,
Lin
,
C.
,
Gorb
,
S. N.
and
Rajabi
,
H.
(
2023
).
Strong attachment as an adaptation of flightless weevils on windy oceanic islands
.
J. R. Soc. Interface
20
,
20230447
.