Hermit crabs and cockroaches emerge as unlikely seed dispersers on a Japanese island

In the humid, coastal forests of Japan’s Ishigaki Island, near Okinawa, scientists have discovered that land hermit crabs and cockroaches serve as unlikely seed dispersers for a parasitic plant called fungus root (Balanophora fungosa). This non-photosynthetic plant grows as a parasite on the roots of trees in island forests across Asia, Australia, and the Pacific. The plant has fleshy, dull-colored fruits containing millions of seeds.

Researchers initially hypothesized that gravity might help disperse these seeds. However, in a recent study, lead author Kenji Suetsugu found that on Ishigaki Island, the seeds are primarily dispersed by land hermit crabs (Coenobita brevimanus) and the Australian cockroach (Periplaneta australasiae). To determine the actual dispersers, the researchers conducted exclusion experiments using mesh nets, covering some plants with them. The nets allowed only tiny ants inside but kept larger animals out.

To their surprise, the fruits inside these ant-only nets were completely untouched. Next, the researchers set up waterproof digital cameras programmed to take photos every 50 seconds. Over nearly 89 hours of monitoring, the cameras captured images of land hermit crabs and cockroaches gathering under the cover of night to eat the fruits. The biggest surprise was the finding that cockroaches, known for being scavengers, were the main dispersers of these seeds.

This unexpected discovery highlights the diverse range of creatures that contribute to seed dispersal processes in nature.