SEPTEMBER
1998

 

 

 

By
Tom Turpin
 
Professor of
Entomology
Purdue University

 

 

 

 

 

9-24-98

Black Moths Could be Spirit of Darth Vader

Moths have been widely held by many ancient people to be the souls of departed humans. It is a belief no doubt supported by the observation of these night-flying insects fluttering around candles, especially during funeral wakes when thoughts of human mortality are likely to surface.

This fall has brought an outbreak of moths. Not your run-of-the-mill light brown moths. These are rather sinister-looking dark brown, black-spotted moths. These moths are not reincarnations of Darth Vader of Star Wars fame, even though they appear other worldly.

The moth has no relationship to outer-space creatures, Star Wars or otherwise. It is a plain old everyday moth. Although, unlike most moths, when at rest its wings form a triangle the moths frequently spend the day in the shelter of vegetation. When numbers are high, driving or walking through resting sites produces a flurry of moth activity as the insects scurry from one hiding site to another. The moths also like to hide in the vicinity of buildings such as our houses or barns. Consequently, human encounters can be frequent when moth populations are high.

The immature of the moth is a green worm that sometimes feeds on clover. Hence, the insect is known by the unimaginative but descriptive name of green cloverworm.

The green cloverworm spends the winter in either the moth or the pupal stage. It emerges from its winter hibernation when plants green up in the spring. The females lay their eggs on the underside of plant leaves. The worms will feed for about a month before they crawl into the soil to pupate. In two to three weeks another brownish-black, triangle-shaped moth emerges.

Green cloverworms feed on many types of legume plants. Alfalfa, beans, soybeans, vetch, and cowpeas are good food for hungry worms of this insect. They also will feed on raspberries and strawberries and a number of weed species. It is a widely distributed species and can be found from the plains states to the eastern seaboard.

Since it does attack crops, the green cloverworm is considered a pest insect. Especially when it begins to eat the leaves of a crop such as soybeans. When this happens soybean growers take a dim view of the little green worm.

An unusual aspect of this insect is that its normal populations are quite low. Under these circumstances there are seldom enough of the moths around to attract attention. In some years, and this was one of those years, moths show up in high numbers. From lawns to weed patches to crop fields, the fluttering moths attract the attention even of people who normally don't notice insects.

In general, high populations occur only every 12-15 years or more. That is good news to soybean growers and folks who do not like to see moths fluttering on lawns or in windows.

The green cloverworm is not the only insect that shows high population numbers every 15 years or so. Several insects exhibit the same type of cycle. Such cycles are due to predators, parasites or disease organisms that keep the insect numbers in check. In other instances it is a genetic mechanism in the insect that controls the numbers.

No one is sure what is involved when the green cloverworm reaches high numbers such as have been present this fall. We are relatively sure though that these moths are not something that arrived on earth from the Starship Enterprise!

 

Writer: Tom Turpin
Editor: Olivia Maddox