Air-entrapping capacity in the hair coverage of Malacosoma castrensis (Lasiocampidae: Lepidoptera) caterpillar: a case study

Abstract

The moth Malacosoma castrensis (Lasiocampidae) is commonly found along the Northern Germany coasts, the habitats of which are mainly represented by salt marshes subjected to sea level variations. Surprisingly, terrestrial caterpillars can withstand many hours of being flooded by seawater. The ability to withstand periods of submersion in a terrestrial insect raises the problem of respiration related to avoiding water percolation into the tracheal system. In the present study, we investigated under laboratory conditions the role of water-repellent cuticle structures in oxygen supply in caterpillars of M. castrensis submerged in water. For this purpose, air-layer stability tests using force measurements, and micromorphology of cuticle structures using SEM and fluorescence microscopy, were performed. A plastron appeared when a caterpillar is underwater. The stability, gas composition and internal pressure of the plastron were estimated. The plastron is stabilized by long and scarce hairs, which are much thicker than the corresponding hairs of aquatic insects. Thick and stiff hairs with sclerotized basal and middle regions protrude into the water through the plastron–water interface, while substantial regions of thin and flexible hairs are aligned along the plastron–water interface and their side walls can support pressure in the plastron even below atmospheric pressure. Additional anchoring points between hair's stalk and microtrichia near the hair base provide enhanced stiffness to the hair layer and prevent the hair layer from collapse and water entering between hairs. The advancing contact angle on hairs is more than 90 deg, which is close to the effective contact angle for the whole caterpillar.

Convergent evolution of skin surface microarchitecture and increased skin hydrophobicity in semi-aquatic anole lizards

“…First and foremost, it may enable ‘plastron respiration’ by capturing and retaining an air film (termed plastron) in the water that can be used as an underwater oxygen supply ( Flynn and Bush, 2008 ; Shirtcliffe et al, 2006 ). Plastron breathing is well known from several semi- and full-aquatic arthropods ( Balmert et al, 2011 ; Ege, 1915 ; Kovalev et al, 2020 ; Thorpe, 1950 ), but had not been described in a vertebrate species until Boccia and colleagues (2021) recently discovered it in several anoles. Boccia et al (2021) report that semi-aquatic anoles rebreathe underwater via recurrent inhalation and exhalation of an air bubble around the lizard's nostrils.…”

Staying Dry and Clean: An Insect’s Guide to Hydrophobicity

“…Other Lepidopterans have similar superhydrophobic wing arrays ( Table 2 ). As a caterpillar, the ground lackey moth ( Malacosoma castrensis ) is hydrophobic as well [ 97 ]. The cuticle of the caterpillar is covered in microtrichia and setae which enable it to form a compressible plastron of air around its body when submerged in tidal zones up to 8 h, twice a day [ 97 ].…”

Submergence tolerance in immature stages of the stalk‐eyed fly Sphyracephala detrahens (Diptera: Diopsidae)

“…Insects with mobile developmental stages can avoid rising floodwater via escape reactions such as running, climbing, and flying to upland areas or higher vegetation (Adis & Junk, 2002;Batzer & Wu, 2020;Wantzen et al, 2016). Some insects with less mobile or sessile developmental stages can survive inundation for several hours to several months (Brust et al, 2005(Brust et al, , 2007Brust & Hoback, 2009;Cavallaro & Hoback, 2014;Clark & Richmond, 1962;Forschler & Henderson, 1995;Hoback, 2011;Hoback et al, 1998Hoback et al, , 2002Joy & Pullin, 1997;Kolesnikov et al, 2012;Kölsch, 2001;Kovalev et al, 2020;Li et al, 2019;Mądra-Bielewicz et al, 2017;Magni et al, 2021;Nielsen & Christian, 2007;Reigada et al, 2011;Singh & Bala, 2011;Singh & Greenberg, 1994;Tamm, 1984;Webb & Pullin, 2002;Wyatt, 1986;Yee, 2021;Zerm & Adis, 2001). Temporal inundation is expected to affect the population growth rate and distribution of insect populations.…”