Adult Lygodium spider moth, Siamusotima aranea. (Image courtesy Chris Bennett, University of Florida.)

Scientists Identify New Moth That Attacks Invasive Fern

By Luis Pons
August 17, 2005

The search for natural enemies of an invasive weed that threatens Florida's wetlands has led scientists to a unique insect: a stem-boring moth caterpillar, dubbed the "Lygodium spider moth," that attacks ferns.

The moth, Siamusotima aranea Solis & Yen, was found in Thailand in stems of a native fern, Lygodium flexuosum, by Agricultural Research Service (ARS) scientists and colleagues seeking biological controls of the Old World climbing fern, Lygodium microphyllum.

The moth was named by two scientists who were the first to identify and describe it: M. Alma Solis of ARS' Systematics Entomology Laboratory (SEL) in Washington, D.C., and Shen-Horn Yen of National Sun Yat-Sen University in Taiwan.

SEL researchers in Washington and Beltsville, Md., identify scores of insects each year that were previously unknown to science.

Entomologist Robert Pemberton observes invasive Old World climbing fern overtaking cypress trees in southern Florida. Click the image for more information about it.

While there are many stem-boring moths, S. aranea is the first to be identified among fern-feeders in Asia, according to Solis. The moth is unique in a number of ways. For one, its caterpillar form looks more like some beetle larvae.

The moth has armored segments on its rear similar to those on beetles but unlike anything seen before in a moth. And the adult moth may mimic spiders, a characteristic that has led to its scientific name, "aranea," as well as its unofficial moniker.

This discovery expands possibilities for biological control of the Old World climbing fern in the United States. The plant is not a pest in its native Australia, South and Southeast Asia, and Africa, perhaps because its enemies keep it in check there.

Already, entomologist Robert Pemberton of the ARS Invasive Plants Research Laboratory in Fort Lauderdale, Fla., is culturing S. aranea to test its effectiveness against the Old World climbing fern.

Scientists in the ARS Australian Biological Control Laboratory at Brisbane -- led until recently by entomologist John Goolsby -- and colleagues have searched Southeast Asia and Australia for natural enemies of this fern since 1998.

ARS is the U.S. Department of Agriculture's chief in-house scientific research agency.