Flying insects’ wings must hold up to millions of cycles of mechanical forces, deformations, and minor impacts, while also being extremely lightweight in order to optimize flight performance. The hind wing of the migratory locust S. [Schistocerca] gregaria is composed of thin and fragile membrane cells supported by a lattice structure of veins which increase the wing’s toughness by 50% and act to distribute stresses during flight and prevent crack propagation.
The morphological spacing of most wing veins matches the “‘critical crack length’ of the membrane, which is determined by the material’s fracture toughness and the stress applied. At a given stress, any crack smaller than the critical length would have no structural effect. As a consequence, the largest possible cell size that prevents cracks from self propagating corresponds to this critical crack length. If a crack is contained within this cell, it cannot reach a critical length to self propagate through the rest of the wing. Any cell bigger than this critical crack length would allow the initial crack to start growing. However, any cell smaller than this critical crack length would be a ‘waste’ of vein material.” (Dirks and Taylor 2012: 7)Edit Summary
“One part of the insect body which needs to resist repeated high mechanical stresses are the wings; in particular those of long distance flying insects such as the desert locust Schistocerca gregaria. In their migratory stage, these insects can fly for days over several thousand kilometres in search of new habitats. During this time their wings are subject to deformation, torsion and bending for millions of cycles…In most biological materials small defects due to wear and tear are inevitable and, rather than trying to prevent cracks, many organisms have adapted to either repair or withstand small defects in their structural tissues…However, due to the histological structure and morphogenetic development of the wing membrane as part of the locust’s exoskeleton, the repair of cracks is not possible. This leaves only the option to minimize the effect of small defects by stopping them as soon as possible.” (Dirks and Taylor 2012:1)
“Our results show that the venation of the locust hind wings not only qualitatively but also quantitatively follows a remarkably uniform pattern. Local distribution and also the total number and the size of cells were almost identical in each hind wing. As our fracture toughness results show, the wing veins are effective crack barriers. The presence of cross veins significantly increases the effective structural fracture toughness of the wing by 50%…” (Dirks and Taylor 2012:7)