The diving bell and the spider: the physical gill of Argyroneta aquatica

Abstract

Argyroneta aquatica is a unique air-breathing spider that lives virtually its entire life under freshwater. It creates a dome-shaped web between aquatic plants and fills the diving bell with air carried from the surface. The bell can take up dissolved O2 from the water, acting as a ‘physical gill’. By measuring bell volume and O2 partial pressure (PO2) with tiny O2-sensitive optodes, this study showed that the spiders produce physical gills capable of satisfying at least their resting requirements for O2 under the most extreme conditions of warm stagnant water. Larger spiders produced larger bells of higher O2 conductance (GO2). GO2 depended on surface area only; effective boundary layer thickness was constant. Bells, with and without spiders, were used as respirometers by measuring GO2 and the rate of change in PO2. Metabolic rates were also measured with flow-through respirometry. The water–air PO2 difference was generally less than 10 kPa, and spiders voluntarily tolerated low internal PO2 approximately 1–4 kPa before renewal with air from the surface. The low PO2 in the bell enhanced N2 loss from the bell, but spiders could remain inside for more than a day without renewal. Spiders appeared to enlarge the bells in response to higher O2 demands and lower aquatic PO2.