Some spiders possess remarkable adaptations allowing them to survive submerged for surprising durations. This ability sparks curiosity, as spiders are typically recognized as terrestrial creatures.
Spider Respiration
Spiders are air-breathing arthropods, requiring atmospheric oxygen. Their respiratory systems primarily consist of book lungs and/or tracheae. Book lungs are sac-like structures with multiple folds that increase the surface area for gas exchange. Air diffuses into the hemolymph through these thin walls.
Many spiders also possess a tracheal system, a network of tubes delivering oxygen directly to tissues. The presence and arrangement of these respiratory organs vary among species. This reliance on atmospheric air means spiders cannot extract oxygen directly from water, unlike fish.
Underwater Breathing Mechanisms
Spiders that venture underwater employ specific mechanisms to carry or access air. One common strategy involves trapping an air bubble against their body, facilitated by a dense layer of hydrophobic, or water-repellent, hairs. This air bubble acts as a physical gill, allowing oxygen from the water to diffuse into the bubble as the spider consumes it.
The diving bell spider, Argyroneta aquatica, takes this adaptation further by constructing a dome-shaped web underwater between aquatic plants and filling it with air from the surface. This silk structure, known as a “diving bell,” serves as a more stable and continuous air supply. The air bubble within the bell functions as a physical gill, extracting dissolved oxygen from the water. This allows the spider to remain submerged for extended periods, only needing to surface occasionally to refresh its air supply.
Duration of Submerged Survival
The length of time a spider can survive underwater varies significantly, influenced by species, activity level, water temperature, and oxygen concentration. For many terrestrial spiders, accidental submersion might last only a few minutes before drowning becomes a risk. Some tropical species, however, hide underwater for up to 30 minutes by retaining an air film, often to evade predators.
Spiders with more specialized aquatic adaptations can endure much longer. Fishing spiders (Dolomedes) can remain submerged for several minutes, sometimes up to 30 minutes or longer, by encasing their bodies in an air bubble. The diving bell spider (Argyroneta aquatica) can stay underwater for over 24 hours, with some reports suggesting up to 48 hours, by maintaining its specialized diving bell. This extended survival is possible because their diving bell acts as a physical gill, continuously drawing oxygen from the water.
Reasons for Underwater Excursions
Spiders venture into aquatic environments for several behavioral reasons. A primary motivation is to escape from predators, such as birds or larger insects, by diving beneath the surface.
Another significant reason for underwater excursions is hunting. Many semi-aquatic spiders, like fishing spiders, actively pursue aquatic prey. They detect vibrations on the water’s surface, indicating the presence of small fish, tadpoles, or aquatic insects. These spiders dive to capture their prey, with some fishing spiders even capable of catching small fish up to 2.5 times their own body weight. Additionally, spiders might seek new habitats or shelter during periods of flooding, temporarily adapting to submerged conditions.