Cockroaches spread seeds, too, research shows

Aug. 3 (UPI) -- Like birds and mammals, cockroaches spread seeds, too.

The insects are mostly known for their role as decomposers, helping to break down decaying matter on the forest floor. But cockroaches also help disperse seeds.

Scientists in Japan found cockroaches were essential to the seed dispersal of a forest herb species, Monotropastrum humile.

The herb is an unusual plant. It has no chlorophyl, leaving it unable to perform photosynthesis. Instead, the species gets its nutrients from fungi growing beneath the soil's surface.

The plant drops tiny, odorless, pale white fruits on the forest floor. The fruits have little to no flavor, and researchers in Japan found bird and mammal species were uninterested in the food source.

Only a handful of invertebrate consumed the fruit's pulp, and the forest cockroach, Blattella nipponica, was the only species to visit the fruit consistently.

Researchers examined cockroach feces to determine whether the insects helped disperse the plant's seeds. Scientists found each feces pellet expelled after eating the fruit featured an average of three seeds.

Further testings proved the majority of digested seeds were viable.

Scientists hypothesize that the unique herb species likely evolved to take advantage of the cockroach's ability to disperse seeds. The plant hangs its fruit at ground level, and the fruits ripen at the same time cockroaches emerge from their pupa stage.

Researchers published their findings this week in the Botanical Journal of the Linnean Society.

"Given that about 4,600 cockroach species have been identified to date, cockroach-mediated seed dispersal may be a more pervasive but an as yet undocumented mechanism, rather than a unique exploit by a particular plant species," Naoto Sugiura, an associate professor at Kumamoto University, said in a news release. "It is hoped that the findings reported here will encourage people to pay more attention to plant-cockroach interactions and seek out further examples of cockroach-mediated seed dispersal."