Arcyria denudata

Arcyria denudata produces some of the most visually striking structures in the slime mold world—brilliant red or pink fruiting bodies that expand dramatically as they dry. The immature fruiting body is a compact cluster; as it matures and dries, it unfurls into delicate net-like structures (capillitia) that hold and gradually release spores. This passive mechanism—using humidity changes to drive expansion—disperses spores without active movement.

The expansion mechanism represents an elegant physical solution to dispersal. The capillitium threads are hygroscopic—they absorb water when humidity is high and release it when humidity drops. This changes thread length and tension, causing the structure to expand and contract with weather cycles. Each expansion releases some spores; repeated cycles distribute spores over time and across varying wind conditions. The organism converts environmental energy (humidity fluctuations) into dispersal work.

A. denudata's strategy contrasts with active dispersal mechanisms like the explosive spore release of some fungi. Passive, humidity-driven dispersal may be slower but requires no metabolic investment after fruiting body construction. The trade-off between active and passive mechanisms mirrors trade-offs throughout biology: immediate energetic cost versus long-term maintenance, rapid single events versus slow continuous processes. Arcyria demonstrates that effective solutions don't always require active investment—sometimes building the right structure and letting physics do the work suffices.