Then they realized that they hadn’t been paying attention to whether the grasshopper was head up or head down in the container that held it. Grasshoppers, like other insects, get oxygen through tubes, or trachea that are open to the outside air and branch into smaller and smaller tubes in the insect’s body. All insects have these, and some have air sacs, to store and pump air, as grasshoppers do.
It turned out that the tubes were more compressed at the bottom of the animal, because gravity was causing the grasshopper equivalent of blood to sink to the bottom half of the animal.
This is similar to what happens when humans stand up quickly and become lightheaded, or the way blood goes to the head during a headstand. Humans have valves in the circulatory system to combat this problem, and your heart rate can increase, to pump blood faster.
But insects don’t have the same system. A grasshopper has a heart, but most of its body had been thought to be like one big bag of blood. Nonetheless, the researchers found that the grasshoppers could substantially counter the effect of gravity when they were conscious. When they were anesthetized with nitrogen, they could not.
The researchers found that the grasshoppers could change the pressure in different parts of their body. And the animals were able to keep different pressure in different parts of the body. How they do it is the next question. But they must have some way of blocking off the abdomen from the thorax, say, to create different pressures.
The discovery reveals something brand-new about the intersection of physics and biology. For now, it seems to be true in grasshoppers, at the least, and probably beetles, based on another study of Dr. Socha’s. But all insects are going to be subject to the same physical forces, which few scientists have ever paid attention to before. And it seems unlikely, said Dr. Socha, that grasshoppers are the only ones to evolve coping mechanisms.
Still, it may be that smaller insects, like fruit flies, don’t need to regulate their bodies in the same way. Dr. Hu said that ants maintain the same metabolism whether they are walking horizontally or straight up a wall. Future studies will show at what size insects have these adaptations, and what exactly they are.