Orchids on the Decline

Earthworms Eat Orchid Seeds
Think twice before you order earthworms to improve the soil of your garden.  A group of scientists from the Smithsonian Environmental Reserach Center (SERC) in Anne Arundel County and John’s Hopkins University Department of Earth and Planetary Sciences in Baltimore recently published a study that shows the damage non-native earthworms, who creep their way into forests thanks to human activities like gardening, may cause to one of the world’s favorite flowers, the orchid.

The study focused on Rattlesnake Plantain Goodyera pubescens, a tall, erect plant with white flowers common in Maryland, including those around the SERC campus in Edgewater, Maryland. The problem with earthworms, the scientists found, is that they reduce Goodyera pubescens’ numbers by ingesting their seeds, which are the size of dust specks and fall into the soil surrounding orchids when the plants flowers.  As earthworms munch through the dirt, they swallow the microscopic seeds, preventing germination in two ways:  Either the ingestion process kills the seeds before they make it out the earthworm’s other end, or the seeds survive ingestion but are reintroduced into the soil too deeply to access upper-level fungi nutrients required for growth.


The research team at Hopkins, measured the effect of both possibilities over six weeks.  They determined almost 80 percent of the seeds ingested in this time period could no longer grow, and almost a third were buried too deeply to flourish.  By a conservative estimate, the study concludes, older forests – 120 to 150 years old – around SERC would lose 49-percent of Goodyera orchid seeds to earthworm ingestion in a year, and younger forests – 50 to 70 years old, where non-native earthworms flourish would lose 68 percent.