Mountain-Prairie Region

 

 

FEATURE SERIES


U.S. FISH AND WILDLIFE SERVICE
134 UNION BOULEVARD
LAKEWOOD, COLORADO 80228

Vol. II, No. 4

4. For Lack of a Moth, the Orchid Is Lost

The western prairie fringed orchid stands as one of the gems of North America's remaining tallgrass prairies. This flowering orchid may grow to 4 feet tall, comparable in height to the surrounding prairie grasses, and may have up to two dozen white to creamy white fringed flowers.

Curiously, the regal appearance of this plant does not attract insects to pollinate the plant during the daylight. Rather, as night descends over the prairie, the orchid's flowers increase its fragrance to attract the roaming moths. Shrouded in this cover of darkness, the long-tongued hawkmoth rises to visit the intoxicating flowers.

"Ironically," notes Kathy Martin, a botanist with the U.S. Fish and Wildlife Service in Bismarck, North Dakota, "this moth is unremarkable in appearance and coloration. What's unusual about it is its uniquely evolved tongue for harvesting the orchid's nectar. The orchid's white fringed petals direct approaching moths to the spur and the plentiful supply of nectar it holds." As the moth hovers with its long tongue extended into the spur, two specialized pollen-bearing structures brush pollen onto the eyes of the moth.

The western prairie fringed orchid nectar spur is the longest of any North American orchid. Only those species of hawkmoths with suitable length tongues and properly spaced eyes can act as pollinators.

After attaching to the eyes, the pollen may be deposited upon the next orchid flower the moth visits. This transfer of pollen among orchids results in fertilization and ultimately the production of seeds.

The remarkable relationship between the long-tongued hawkmoth and western prairie fringed orchid has been continuing successfully for centuries until European settlers settled the heartland of North America. "They found the tallgrass prairie yielded fertile soils, ideal for raising a variety of crops," said Martin. "Millions of acres of America's prairies were rapidly converted for cropland. Today we have only about two percent left of the tallgrass prairie and less than 40 percent of the original western prairie fringed orchid populations."

Today, tallgrass prairie has generally been reduced to small islands in a sea of cropland, and the orchid, facing potential extinction, was listed as a threatened species under the Endangered Species Act in 1989.

The fragmented prairie landscape created by man poses the greatest obstacle for these insect-oriented orchids. The expanses of cropland act as a barrier for free movement of hawkmoths between different orchid populations, reducing genetic diversity of isolated stands. Pesticide drift from nearby cropland also poses a threat to non-targeted insects such as the hawkmoth. In some areas, hawkmoth numbers are so depleted that only a very small percentage of flowers are pollinated and produce seed.

These remaining tallgrass prairie tracts must also be intensively managed to prevent native trees and shrubs from invading and shading orchids out, or by exotic weeds such as leafy spurge that can displace the orchid and other native prairie vegetation.

Approximately a quarter of known western prairie fringed orchid sites are protected in preserves or other publicly-managed areas. Land managers are concentrating their efforts on meeting the orchid's needs through implementing long-term management plans.

Providing hawkmoth "corridors" of native prairie between orchid populations could offset the immediate threat that faces isolated populations. However, some orchid preserves are isolated tens or even hundreds of miles apart. For these secluded populations, pollinating the plants by hand can buy the orchid some time until their prairie habitats can be rejoined and pollination can be reclaimed by its original masters.

Long-term survival of this tallgrass prairie gem requires not only protecting its habitat but also insuring the survival of the orchid's only means of reproduction, the long-tongued hawkmoth.


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