Are Insects a Blessing or a Curse?
WHAT comes to your mind when insects are mentioned? Do you think of insects that spread disease, feed on man’s crops and eat holes in his clothing?
Or do you think about the benefits insects bring? Do you think of the services they perform and the products they yield—shellac, silk and honey, to mention a few?
To some it may seem that all insects are pests and that the world would be better without them. But did you know that, of the more than 800,000 kinds of insects known to man, the vast majority are acknowledged to be beneficial? In fact, many of them do things that are vital to man’s existence.
Pollinating and Building Soil
One such vital service has to do with the relationship of insects to plants. It has been estimated that 85 percent of flowering plants are dependent on insect pollination.
Among the many insects carrying out this function are honeybees, bumblebees, flies, beetles, moths and butterflies. And if such insects did not do their job, many of these plants, perhaps most of them, would die out. That would affect, not only the beautiful flowers that add so much enjoyment to man’s life, but also his food supply. Man would indeed be in big trouble.
Insects also play a beneficial role as scavengers and soil builders. Dead plant and animal matter attracts many kinds of insects. They eat this dead matter and their digestive systems break it down into different chemical combinations. In this way the dead matter is turned into food that can be used by plants.
Not only their excreta, but the insects themselves eventually turn into food for plants. This happens when they die and their bodies decompose, in this way adding fertilizer to the soil.
Insects also help to add to the thickness of rich topsoil. This is done by insects continually bringing up particles of sub-soil to the surface. In the process they dig tunnels in the soil, and this helps too. It enables water to filter down through the soil and it aerates it at the same time.
What About Insects That Eat Plants?
But insects also eat live plants, not just dead ones. Is this not harmful to man’s interests? Not necessarily.
Careful observation and research indicate that insects prefer plants that are in some way deficient from our standpoint. It may be poor soil, the plant’s age or some unfavorable growing condition that was responsible for the deficiency.
When the plant does become deficient, it attracts insects. For instance, Dr. William Albrecht of the University of Missouri conducted a series of tests with spinach. He found that insects known as thrips destroyed the spinach grown on poor soil. But the spinach grown on good soil survived.
Then there was the case of two grapevines growing side by side. One was attacked by Japanese beetles, but the other was not. Yet the leaves of both vines were intermingled. The beetles fed only on the leaves of the older vine, which was not responding well to the nutrition being given to it.
A similar observation was made about two crops of lettuce. One crop had been stunted by unfavorable growing conditions and was attacked by aphids. But no aphids were found on lettuce cultivated under favorable growing conditions in the same soil.
Commenting on why insects prefer plants that we would consider inferior, the book Our Poisoned Earth and Sky states:
“The nutritional needs of insects are very different from those of man and animals. Where man thrives best on a high protein diet, insects go for carbohydrate. They need it more in their system of operation. An insect can jump the equivalent of the Empire State Building in one jump, comparatively speaking, and it needs a lot of carbohydrate for that energy. So when one plant has more carbohydrate than another, an insect will seek it out and prefer it.”
Verifying this observation by scientific research, the book continues:
“As research at the Missouri Agricultural Experiment Station has shown, plants which get no organic matter produce an unbalanced amount of carbohydrates at the expense of protein and trace minerals. Insects, it seems, prefer these ‘sweet’ plants and are able to attack them more easily.”
So when insects eat garden plants, might they not be telling us something? Are the plants receiving needed nourishment from the soil? Can something be done to remedy an unhealthy condition in the plants?
Many insects show a preference for a particular kind of plant. Their feeding habits prevent various plants from running riot.
A case in point is the prickly-pear cactus. This plant was unwisely introduced into Australia. There being no insect enemies to keep it in check, the prickly-pear cactus spread rapidly. Within a short time it made millions of acres of land practically unfit for agriculture.
Then, in 1925, 2,750 cactus-moth eggs were sent to Australia from Argentina. Eventually millions of moth eggs were distributed in areas where the prickly-pear cactus had gained a foothold. The hatched caterpillars of the cactus moth did their job well. They burrowed into the joints of the prickly-pear cactus and thus destroyed it. At last this cactus ceased to be a scourge for Australia.
Another example of plant control by insects involves St.-John’s-wort or the Klamath weed. This weed was brought to the United States from Europe. It was first noted in the United States in 1793. By 1940 thousands of acres of rangeland in northern California were ruined by this weed. Later its European insect enemies were introduced. Regarding the effectiveness of this measure Scientific American states:
“The destruction of Klamath weed by the beetles has been attended by the return of desirable forage plants. In California many thousands of acres now have a markedly greater capacity for the support of livestock; land values have risen; expenditures for the control of the weed are negligible.”
But have these insects become a pest since the time the Klamath weed was brought under control? No. Scientific American continues:
“Because stands of Klamath weed are no longer extensive and the infested areas are now widely separated, all of the immigrant insects, totally dependent on the weed for survival, have decreased in numbers. Fortunately their ability to locate new infestations and their high rate of reproduction have prevented any important resurgence of the weed. All indications are that this noxious range plant will be held in check and that its insect controls will perpetuate themselves.”
There is no way of knowing just how many plants could become pests if it were not for insect control. But the foregoing examples well illustrate that man needs the help of insects.
Even insect activities that seem to be destructive can benefit man. In the forests, insects perform vital pruning work. Some attack and kill the lower limbs of trees. This natural pruning gives man better quality lumber. Still other insects kill trees. Thereby they prevent wooded areas from becoming overcrowded. Surviving trees are enabled to grow more rapidly. The activity of forest insects also reduces the fire hazard and makes the forest more suitable as a home for wildlife.
Man Still Has Much to Learn
Man’s knowledge of insects is still very incomplete. Each year from 7,000 to 10,000 new kinds of insects are discovered. The relationship of thousands of insects to plant and animal life is unknown. But what has been learned shows that insects occupy a very important place on earth. Observed Carl D. Duncan, a professor of entomology and botany:
“It is perhaps impossible to visualize adequately the totality of beneficial effects which insects exert directly or indirectly on human welfare, but the benefits are incalculably great.”
Often the negative side of what insects do gets major attention. The fly, for example, is commonly associated with the transmission of disease. But how many persons think about its role as a scavenger and soil builder and maintainer when in the maggot stage? And did you know that the guilt of houseflies has not been fully established? Says Scientific American:
“The list of human and animal diseases they are charged with transmitting now stands at more than 65. . . . Yet the evidence is still only circumstantial. The reputation of the domestic flies is in the position of a man charged with homicide because he is found standing beside the victim with a loaded gun in his hand. In most cases it cannot be proved conclusively that the flies in question fired the gun.”
Insects a Blessing
While some insects may be harmful under the present circumstances, as a whole they are a blessing for mankind. When insects become pests, humans are often to blame. Man has repeatedly failed to maintain a high standard of cleanliness. He has upset the balance between plant and animal life and has polluted air, land and water. Imbalances in his own system may at times make his body attractive to such insects as mosquitoes. Manifestly, insects, governed by instinct, cannot be blamed for what they do because of man’s failings and weaknesses.
Persons who acknowledge the existence of a loving Creator see in insects a part of God’s creation. This prevents them from drawing hasty conclusions about the harmfulness of any creature. They also appreciate that present circumstances cannot be used as a basis for determining what effect insects would have on men free from all bodily imperfections and weaknesses. They are confident that insects will continue to be a blessing for mankind.