Bird’s nest fungi launch spore packages with falling water

Spore packages inside a tiny cup

Fungi in the family Nidulariaceae can resemble miniature bird nests. Their apparent eggs are peridioles: packages containing spores. They occur on substrates including decomposing wood and wood-chip mulch. The resemblance makes the fruit bodies memorable, but a small water-catching cup is a better guide to how they work.

Maribeth Hassett and colleagues tested this mechanism in a study published in Fungal Biology in 2013. They examined fruit bodies of four species in Cyathus and Crucibulum, collected on the Miami University campus in Ohio. High-speed cameras recorded their movements at 3,000–6,000 frames per second.

Water supplies the launch energy

The experimental drops fell from a height of 1.2 metres. At roughly 6 mm across, they resembled large drops shed from wet vegetation rather than typical small raindrops. Impacts near the rim were most effective: the displaced water propelled a spore package upwards. Drops striking the centre did not produce the same effective ejection.

The paper reports launch speeds on the order of 1–5 metres per second. An estimated maximum horizontal range of about a metre came from modelling trajectories using the measurements. It is not a claim that every peridiole travels that far. Species, package mass, launch angle and initial speed all affect the outcome.

The cord deploys on contact

The recordings revealed another part of the mechanism. A peridiole flies with its funicular cord still condensed. When the sticky end contacts an obstacle, the cord unravels. The moving package helps wind it around the support, braking its flight and leaving it attached. Short pieces of floral wire represented vegetation in the laboratory experiments.

This corrects an easy shortcut in descriptions: the cord is not an open parachute trailing throughout the flight. It deploys when the sticky end meets the surroundings. The fruit body uses energy from falling water to launch the package, while the package carries a separate mechanism for stopping and fastening itself to a new surface.

This account condenses and explains research by Hassett and colleagues, whose paper is available under a CC BY licence.