Figure 1

Morphological properties of Argyroneta webs. A: Top view of the experimental equipment for keeping water spiders. 1. specimen with its plastron, 2. anchor threads (see arrow) and various layers of sheet-web, 3. small, new diving bell and tunnels. B. Side view of the air volume of a one-night-old diving bell (max. width 20 mm) set beneath a slightly raised sheet-web (locally restricted by stronger threads anchored on both glass wall and sticks). The spider is sitting just inside its bell. C. Side view of three air bubbles (Ø 1.3–2.6 mm) experimentally placed using a micropipette beneath a sheet-web (the surface of the sheet-web is not visible over the largest air bubble due to its hyaline and thin properties). D. Surface of a sheet-web during early evacuation in a Fei Quanta FEG 250 SEM after it was exposed to air and mounted on an adhesive carbon tab. Its smooth surface has just become cracked. E-H. Threads and hydrogel of both sheet-web and diving bell wall scanned with a Zeiss Axioplan microscope after Coomassie Blue staining. E. Area of a one-night-old sheet-web with only two slightly crossing bundles of silk threads, still without any hydrogel in between. F. Area of a completed sheet-web with both strong and very thin hydrophilic silk threads embedded in a proteinaceous hydrogel. G. Complex structure of a one night-old diving bell wall with crossing strong and fine threads embedded in bluish hydrogel (the scan was processed by a digital contrasting programme). Additionally, one can detect places at which crossing threads are linked together (see arrows). H. Structure of a two-night-old diving bell wall with a strong silk thread splitting into thin threads (or vice versa: fine threads combining to a strong thread?).