Susan Kane, age 14, of Providence, R.I., for her question:
DO INSECTS HAVE INTERNAL ORGANS?
Yes, but internal organs of insects differ in many ways from those of other animals. Insects do indeed have certain chief systems of internal organs: circulatory, respiratory, nervous, muscular, digestive and reproduction systems.
A circulatory system carries blood through the body. The blood does not flow through veins and arteries. Instead, it floods the whole body cavity and bathes all the organs and muscles. An insect's blood, like ours, carries food and waste products to and from the cells of the body. Insects are cold blooded animals.
An insect breathes by means of tiny holes, called spiracles, along the sides of its body. The holes are connected to a complex series of tubes that branch out to all the cells of the body. The system carries oxygen to the cells and takes away carbon dioxide.
Insects have brains that control body activities as a whole. The brain receives information from the eyes and antennae. Nerve cords contain clusters of nerve cells.
The muscular system of insects is made up of several hundred to a few thousand small but very strong muscles. Grasshoppers have about 0 muscles and caterpillars have from 2,000 to 4,000. Humans have fewer than 700 muscles.
Many insects can lift or pull an object 20 or more times heavier than the weight of their bodies. Few people can lift a weight heavier than their own bodies.
The digestive system of an insect consists basically of a long tube that runs from the mouth to the anus. It has a foregut, a midgut or stomach, and a hindgut or intestine.
Food moves through the tube until it reaches an enlarged area called the crop where it is temporarily stored and partly digested.
In the midgut, nourishing parts of the food are absorbed into the blood and waste and undigested parts move into the hindgut and out of the body.
Like other animals, insects can see, hear, touch, taste and smell. Many kinds have senses that are far keener than those in most other animals.
Most kinds of insects have two large compound eyes that occupy most of the head. Each eye is made up of tiny six sided lenses that fit together like the cells of a honeycomb. The number of lenses varies from about six in some worker ants to about 30,000 in some dragonflies.
Insects cannot move to focus their eyes. They have sharp vision for only a short distance. They see objects more than a yard away only as a blur.
Insects have a wide range of hearing. Some can hear ultrasonic sounds more than two octaves higher than a human being can hear. Insects are highly sensitive to touch as well as to taste. The sense of smell is located chiefly in the antennae of insects. Most species have a keen sense of smell that is used to locate food, to find their way about and to locate places to lay their eggs.