Simultaneous optimisation of earwig hindwings for flight and folding

Abstract

Earwig wings are highly foldable structures that lack internal muscles. The behaviour and shape changes of the wings during flight are yet unknown. We assume that they meet a great structural challenge to control the occurring deformations and prevent the wing from collapsing. At the folding structures especially, the wing could easily yield to the pressure. Detailed microscopy studies reveal adaptions in the structure and material which are not relevant for folding purposes. The wing is parted into two structurally different areas with, for example, a different trend or stiffness of the wing veins. The storage of stiff or more flexible material shows critical areas which undergo great changes or stress during flight. We verified this with high-speed video recordings. These reveal the extent of the occurring deformations and their locations, and support our assumptions. The video recordings reveal a dynamical change of a concave flexion line. In the static unfolded state, this flexion line blocks a folding line, so that the wing stays unfolded. However, during flight it extends and blocks a second critical folding line and prevents the wing from collapsing. With these results, more insight in passive wing control, especially within high foldable structures, is gained.

Functional diversity of resilin in Arthropoda

“…The occurrence of resilin in several broadened vein patches as well as in membranous folding lines was described for fan-like dermapteran hind wings [22,92]. These structures help folding the wing into a wing package being ten times smaller than the unfolded wing.…”

“…Both unfolding mechanisms are supported by several wing stiffening mechanisms such as the mid-wing mechanism and the claval flexion line, which keep the wing unfolded in all species examined [22,93]. These mechanisms were found to play an important role both in the static unfolded state of the wing and during flapping flight, in which they help to inhibit an unfavorable folding of the wing [92]. Furthermore, the flexible resilin-bearing folding lines were found to not only serve wing folding but also act as flexion lines at which the wing flexes during flight, thereby supporting the generation of an aerodynamically favourable cambered wing profile [92,94].…”

A simulation of the flight characteristics of the deployable hindwings of beetle

“…It is believed that an insect is an excellent biological object for the bio-inspirations to de-sign and develop a MAV. For example, it has been found that the wings of some insects, such as Dermaptera, Coleoptera and Blattaria, become smaller by various folding ways to protect and maintain the functionality on ground meanwhile to provide the necessary aerodynamics for flight [2][3][4][5][6] . It is believed that if the similar mechanism of insect wings' folding is mimicked, MAVs' wings are foldable and their performances can be considerably enhanced.…”

Earwig fan designing: Biomimetic and evolutionary biology applications

“…Once insects gained the ability to withdraw the wings upon their body, multiple ways to decrease the area of the stored wings repeatedly evolved. Earwigs fold their hind wings once fanwise and twice axially, reaching packing areas up to about 1/15 of the original wing surface ( 2 , 3 ). This extreme compactness allows these insects to fully flex their abdomen, enabling them to use their forcepslike cerci ( 4 ) and wriggle into narrow spaces, including digging in the soil ( 5 , 6 ), while usually maintaining fully functional flight capability ( 2 , 7 ).…”

“…Earwigs fold their hind wings once fanwise and twice axially, reaching packing areas up to about 1/15 of the original wing surface ( 2 , 3 ). This extreme compactness allows these insects to fully flex their abdomen, enabling them to use their forcepslike cerci ( 4 ) and wriggle into narrow spaces, including digging in the soil ( 5 , 6 ), while usually maintaining fully functional flight capability ( 2 , 7 ). Unlike the patterns that typically occur in other insects that can fold their wings axially, such as most beetles ( 8 – 11 ), some cockroaches ( 12 ), and a few wasps ( 13 , 14 ), true bugs ( 15 ) and moths ( 16 ), the crease pattern of the earwig wing is conservative across the whole group and likely evolved only once ( 17 ).…”