Their hearts are sort of like one of our arteries, but open at both ends. An insect itself is approximately a hollow, tube shaped shell. Its organs actually float freely around in a pool of its blood, but this substance is more like our sweat than our own blood. The blood carries food and other materials around inside the insect's shell. Like in an aquarium, this process is most efficient if the fluid is circulating, and the insect heart draws blood in from one end of the insect's body and delivers it to the other end. The blood then drifts back to the other end to get pumped again. Insects get their oxygen directly from the air by a dence network of air tubes running through their bodies. The tubes open through tiny holes in the insect's shell. An insect's heart does not carry oxygenated blood like our own does, rather it just keeps the body fluid circulating.