constrictors like Boa constrictor have a problem: they kill their prey by entwining them and literally crushing them to death. But the deadly pressure – action equals reaction – weighs equally on the snake’s chest. And unlike mammals, snakes don’t have a diaphragm: they breathe by moving their costal arches. A team led by John G. Capano from Brown University in Providence in the USA has now carried out experiments to resolve this apparent contradiction. As the working group reports in the Journal of Experimental Biology, the constrictor avoids the problem by specifically moving individual ribs in unblocked parts of the thorax. This causes small areas of the lungs to function like bellows, sucking air into the blocked areas.
In their experiments, the working group wrapped several of the bodies with straps that are normally used to tie off the arm when taking blood Boa constrictor. In this way, the experts prevented the constrictors from stretching the chest in this area – and measured the respiratory flow with small masks. As the team reports, the snakes proved to be mask skeptics, which made measurements difficult. Nevertheless, the data obtained in this way showed that the snakes were still able to breathe despite the restriction. X-rays confirmed the finding. It shows that parts of the snake’s thorax can still expand even when other parts are already immobile.
The animal can do this because it can activate the muscles in different areas of the chest independently of one another. To prove this, the working group measured the potential of nerves that control different muscle groups along the thorax. It became clear that the snakes did not even try to breathe with the restricted area of their thorax. Instead, they only activated the muscles on ribs that could still move. Experts suspect that this ability appeared early in the evolution of these animals, first helping them to devour larger and larger prey without choking. Only later did some species use the special breath control for the special hunting technique of the constrictors.