By Laura & Hal Mahan
Summer is on the wane when you see the gold of goldenrod flowers at the edges of roadsides and in open fields. Goldenrod nectar is a favorite of bees, butterflies, wasps and other pollinators, creating a small microcosm of interesting characters to observe on a warm late summer day.
If you suffer from hay fever or seasonal pollen allergies and are thinking that this beautiful yellow flower is the cause of your affliction, think again! The real culprit is common ragweed, which typically blooms at the same time and sometimes grows in similar open-field disturbed areas. Ragweed (genus Ambrosia), although classified in the same family of plants (Asters) as the goldenrod, has a small, green, non-showy flower with lots of pollen that blows away in the wind.
Goldenrods (genus Solidago), with their much showier flowers, are insect-pollinated. Wind-pollinated plants like ragweed typically produce much more pollen than those pollinated by insects, since their pollen must reach the proper destination by chance instead of by special delivery on the legs of a bee or other insect.
Sometimes you will find a goldenrod plant with a ball or spindle-shaped swollen area called a “gall,” perhaps an inch or two in diameter, at some point on its main stem. The ball-shaped gall is caused by the goldenrod gall fly; the spindle-shaped gall by a moth. Both have similar life cycles, centered around the goldenrod plant.
The small, brown goldenrod gall fly is about 5 millimeters long, and, surprisingly, it does not fly very well. Instead, it walks up and down the stem of the goldenrod plant looking for a mate. After mating, the female lays her eggs inside the goldenrod stem by inserting her sharp ovipositor in the plant tissue.
The larvae then hatch in ten days or so and begin eating the inside of the goldenrod stem. Their saliva contains a chemical which causes the plant to grow abnormally, creating the ballshaped gall inside of which the fly larvae live. The larvae stay inside of their galls for a full year before becoming adults. When fall approaches, the larva digs an escape tunnel in the gall, but still does not emerge until the next spring, staying alive during the winter by producing a kind of anti-freeze inside its body. In the spring each larva will become a pupa (resting stage) before emerging as an adult fly.
Goldenrod nearly became an industrial commodity during World War I when the price of rubber rose from 20 cents to nearly two dollars a pound. Famous American inventor of the light bulb Thomas Edison was asked by his good friend Henry Ford to find a domestic source for latex. Edison became quite the botanist, exploring thousands of species of plants to determine which might contain rubber or latex. Edison determined that goldenrod showed the most promise, but rubber from goldenrod never made it past the experimental stage when it was discovered that synthetic rubber was much easier to produce.
Hopefully, this September you will look at the goldenrod plant with its beautiful, showy clusters of golden flowers with new appreciation and wonder.
Laura and Hal Mahan are owners of The Compleat Naturalist, located at 2 Brook Street in the Historic Biltmore Village. To learn more, visit CompleatNaturalist.com or call 828.274.5430.