Mesothoracic leg showing brush airs used for grooming
Image: Hilda Harpster*
The beetle, Helichus striatus, has hydrofuge hairs that hold the plastron (air bubble) in place. If the plastron is lost, the hydrophobic nature of the hairs dissipate and the hairs become hydrophilic. The hydrophobic coating must be replaced.
Beetles that lose their plastron will climb on sticks to the surface and begin grooming. The hydrophobic substance appears to come from beetle salivary secretions. The beetle has brush-like hairs on its front legs that are repeatedly drawn through its mouthparts during grooming. The brushes of the prolegs are rubbed repeatedly over the head and prothorax and rubbed together with the middle legs. The middle and hind legs are used to groom the wing and posterior portions of the insect. During grooming, beetles may climb completely out of the water, spreading their wings and raising their abdomen to allow the beetle surface to completely dry. After the grooming is complete, the beetles hairs are once more hydrophobic and able to form a plastron.
*Hilda T. Harpster. An Investigation of the Gaseous Plastron as a Respiratory Mechanism in Helichus striatus Leconte (Dryopidae). Transactions of the American Microscopical Society, Vol. 60, No. 3 (Jul., 1941), pp. 329- 358.
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