Kenneth D. Currier, age 14, of Visalia, Calif., for his question:
Do insects have blood like ours?
Insects have blood, but it is not much like ours. True, it is liquid, but only a very few insects have red blood. It circulates through the tiny body, and for this a pumping heart is needed to keep it on the move. Rat an insect's heart is not much more than a tube, and his circulatory system does not have our complex network of veins and arteries.
Our red blood cells contain hemoglobin, a miraculous biochemical that delivers oxygen from the lungs and swaps it for waste carbon dioxide from the living tissues. This day and night operation is part and parcel of the respiratory system, during which we breath fresh oxygen into the lungs and breathe out waste carbon dioxide. Our blood is colored red by hemoglobin carrying rich supplies of oxygen.
An insect's blood has little to do with distributing oxygen and disposing of carbon dioxide. Hence, his circulatory system is not part and parcel of his respiratory system. He does not need swarms of red blood cells, stuffed with hemoglobin. The blood of an insect may be tinged with green or with yellow, and in some species it is colorless.
Its main duty is to carry digested and dissolved foods to where they can be absorbed by the living cells inside the tiny body. This does not require a complex closed network of blood vessels and capillaries to bring the.x2utrients in contact with every cell. Hence, the circulatory system is quite simple. The pale, watery blood supply fills the entire cavity inside the outer exoskeleton.
Nor does it need a high powered heart to keep the bloodstream pumping between lungs and busy cells. The insect's heart is a long tube, where his spine would be if he had one. The blood enters through small slits at sections along the way. Toward the tail end, the heart segments contract to push, or pump, the bloodstream forward, where it opens into the head.
After nourishing the insect's bitsy brain, the blood oozes around to bathe the various organs, and branches stream down to nourish the muscles of the legs. From the thorax, or chest muscles, it enters the stomach, where it gives up waste materials and absorbs a fresh supply of dissolved food. From there it pushes through tiny slits to re enter the tubular, segmented heart.
A blood system of this sort need not work very hard or pulse very fast but obviously, the insect must have some system to do the work done by our red blood cells. This respiratory system also is very different from ours. It opens to the outside air through pairs of small pores in the thorax and abdomen. The air seeps among the cells through a network of branching tubes.
When you swat a mosquito after she has dined on your flesh, you may think that red is the natural color of her blood. Not so. That reddish mishmash is colored by the blood she sucked from your body. Her own blood is a pale, almost colorless watery liquid.