In 1875, an enormous plague of locusts moved across the Great Plains of North America, from Canada to Texas, eating everything in its path. (Locusts are a special form of swarming, migratory grasshoppers that are stimulated to change their color and behavior by crowded conditions.) The 1875 swarm consisted of the Rocky Mountain Locust, Melanoplus spretus. This grasshopper once bred in sandy soils across just a few thousand square miles of the northern Rocky Mountain states and southern Canada. In favorable years, crowding would initiate a migratory behavior in the grasshoppers, and they would sweep down into the Great Plains in almost unbelievable numbers.
Throughout the 1700 and 1800s, periodic swarms of Rocky Mountain Locusts caused serious damage to agricultural crops and grazing land, as well as consuming everything from leather to wood to wool. Trains were sometimes stopped by the huge accumulations of grasshoppers on the tracks. The 1875 swarm was estimated to cover about 198,000 square miles at any one time, as it moved across the continent devastating all plant life in its path. The weight of grasshoppers in the plague was estimated at 27.5 million tons, based on an estimate of 12,500,000,000,000 individuals in the swarm.
Then, suddenly, this species went extinct. The last living specimens of Rocky Mountain Locusts were seen in southern Canada in 1902. Ironically, because the species was so abundant, relatively few specimens were ever collected and preserved in insect collections. Why it went extinct is largely unknown, although the best guess is that agricultural plowing of the sandy soils where it laid its eggs resulted in its elimination.
Despite the disappearance of this troublesome species, outbreaks of other species of grasshoppers still cause considerable agricultural damage in many parts of the western United States and in many other regions of the world. Our local grasshopper outbreaks can be impressive and annoying, but rarely is the damage they cause anything like that caused by the plagues of locusts endured by early settlers to this area in the 1800s.
We have many local species of grasshoppers, but the one that causes the greatest agricultural problems in Mason County these days is the Differential Grasshopper, Melanoplus differentialis. This grasshopper is in the same genus as the Rocky Mountain Locust. However, unlike that now-extinct plague-causing species, the Differential Grasshopper is not migratory, and has only one generation per year. Individuals move no more than a few miles from where they are born. Although these grasshoppers can occur in very large numbers locally, they do not form the migratory plagues of locusts that were witnessed by Mason County residents in the late 1800s.
Each female Differential Grasshopper lays up to six egg masses in sandy soil, and each egg mass can contain up to 200 eggs. That means that a single female grasshopper can produce more than 1,000 offspring, if they all survive. This is why our grasshopper populations can vary so much from one year to the next. When weather conditions are favorable, huge numbers of grasshoppers emerge in the spring and develop through the summer.
The eggs of a Differential Grasshopper start development shortly after they are laid. They then enter a resting period, known as diapause, and remain in a holding pattern through the winter. When the soil warms in late spring, development resumes and the young grasshoppers (known as nymphs) hatch, usually in late May. The nymphs (which look like small, wingless versions of the adult grasshoppers) then go through five life stages, or instars, each successive one of which looks more like the mature adult. Only the final adult stage has wings. The growth of the nymphs takes about a month, and then the adults live and reproduce for another couple of months. This is why we have lots of grasshoppers through our summer, but relatively few through the rest of the year.
Differential Grasshoppers eat both grasses and broad-leafed forbs, and they can be devastating to agricultural crops. Locally, they are especially problematic for home gardeners, as well as for those with vineyards or orchards. When the weather turns dry, the grasshoppers often focus their feeding on irrigated crops and trees. In some years, grasshoppers can strip all the leaves from fruit trees or vines, consume all the fruit, and even girdle tree limbs by consuming bark.
As frustrating as they can be, large populations of grasshoppers do have some benefits as well. In particular, grasshoppers are an important food of many birds, lizards, frogs, and other wildlife. Large grasshopper populations are associated with increased reproductive success of quail, turkeys, and many other birds. For this reason, land owners should carefully consider the measures they use to control grasshopper populations. Insecticides that poison grasshoppers also poison their predators, and these poisons rapidly accumulate in species that feed on grasshoppers. This can result in reproductive failure, or even death of many species of birds. One of the most common questions I get from local landowners is “what happened to all the quail?” There are several reasons for quail decline, but increased use of insecticides is certainly a contributing factor.
There are several alternatives to insecticides for the control or management of large grasshopper populations. For home gardeners, one of the simplest solutions is to use insect netting over and around plants that grasshoppers target in the summer. During the long, hot, dry days of summer, the light shading effect of the netting is also beneficial to most plants. The use of cayenne pepper sprays on plants can also discourage grasshopper feeding, as long as there are alternative food plants available to the grasshoppers.
Another popular solution is to use biological control to reduce grasshopper populations around sensitive crops and gardens. Tiny internal parasites of grasshoppers, known as a microsporidia, can infect and kill the early instars of grasshoppers. One such species, Nosema locustae, is available commercially, and is commonly abbreviated as NoLo. The infectious NoLo are sold in a bait that is attractive to the grasshopper nymphs; as the nymphs eat the bait, they also ingest the microsporidia. Once in the grasshopper’s gut, the microsporidians quickly replicate, and the grasshoppers stop feeding and die. Other grasshoppers eat the bodies of the affected grasshoppers, spreading the infection and greatly reducing grasshopper numbers. Although the microsporidians are lethal to the early instars of grasshoppers, they are not very effective in controlling adult grasshoppers, and they are harmless to most other species, including grasshopper predators, pets, and humans. Applied properly, early in the grasshopper life cycle, NoLo is a highly effective way to locally reduce grasshopper populations around gardens and orchards without harming birds and other grasshopper predators.
Finally, I’ll note that grasshoppers are considered a delicacy by humans in many parts of the world. I have eaten them in many parts of Asia, Africa, and Latin America, where they are relished as a healthy and tasty protein source. They may not appeal to everyone, but if you want to give them a try, a quick internet source will reveal many recipes! Some species of grasshoppers are far more edible than others, however, and be sure that any that you eat have not been feeding on crops that have been treated with insecticides.
—Have a question about science, especially as it relates to Mason County? E-mail me at [email protected] and I will do my best to answer it in this column.
—David Hillis is the Alfred Roark Centennial Professor in Natural Sciences at the University of Texas at Austin, where he directs the Biodiversity Center. He also owns and operates the Double Helix Ranch in Mason County, where he lives.
