A shelter held together by underwater silk
Build with underwater silk
Meet case-making caddisfly larvae, distinguish adhesion from fiber response, and compare one model shelter in two currents.
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Original WebTug explanation with animated teaching diagrams. On-screen text carries the lesson; there is no audio narration.
Diagrams simplify the science. Animation timing and diagram dimensions are illustrative, not measurements of live spiders.
Build and compare a river shelter →Read the full transcript
- Can silk build underwater?
Some caddisfly larvae join gathered materials into protective cases with silk. Caddisflies are insects, and different groups build different silk structures.
- Two material jobs work together
Adhesion attaches silk to a surface. The fiber's mechanical response describes how it deforms under load. Both contribute to a case.
- Build the teaching model
River Shelter gives you six positions and ten silk bonds. Those limits and the material properties are game choices, not biological measurements.
- Current changes the load
For an unchanged piece, this model's load rises with current speed squared. Doubling speed multiplies load by four.
- A design choice has consequences
Turning a twig or leaf reduces its modeled exposure. Extra bonds raise modeled capacity. Neither rule calculates real silk chemistry or survival.
- Compare the same case twice
Keep the design fixed and increase the current. Compare retained pieces and first failure, then explain what the two tests establish.
Scientific sources and media credits
- Wang et al. (2015): Underwater adhesion of caddisworm silk
- Frandsen et al. (2019): Underwater silken architectures
- WebTug: River Shelter model assumptions
Script, diagrams, animation, and editing: WebTug, September 27, 2026. This video adaptation is available under CC BY-SA 4.0; individual photographs retain their credited licenses.
Case-making caddisfly larvae assemble protective structures underwater using adhesive silk. Research on Hesperophylax occidentalis describes an adhesive outer layer around a viscoelastic fiber core. Adhesion attaches the silk to a surface; the fiber’s mechanical response concerns what happens as it deforms. Those are related tasks, but they are not the same property. Wang and colleagues, 2015: study and abstract.
Caddisfly silk supports different underwater architectures, including cases and capture nets. River Shelter focuses on case-making; it does not suggest that all caddisflies build the same structure. Frandsen and colleagues, 2019: comparative silk research.
What your construction lets you investigate
A material can remain attached at one load and fail at a larger load. Keeping a design fixed while changing the current lets you test that idea. If a piece detaches, identify its position and bond count before changing your design. If both tests hold, the evidence says your case survived those two model conditions; it does not establish an unlimited safety margin.
The six slots, ten-bond budget, material inventory, drag coefficients, exposed areas, bond capacities, and damage accumulation are original game rules. The model uses load ∝ exposed area × current speed², and bond capacity ∝ bond count. It does not solve real fluid flow, simulate silk chemistry, measure caddisfly survival, or reproduce the mechanics of a particular species. The case is shown open-ended. The character is a stylized illustration.
Beyond the Web
This section explores the physics of materials animals make, starting with underwater silk. It adds a construction problem to WebTug’s spider challenges. Any future material—silk, adhesive, or another secretion—will be named accurately and connected to its own evidence and experiment.
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