Nine Hearts

Thursday, Sep 29, 2011

Yes, flies have hearts, in fact they have nine. In some way they are similar to your own heart for their purpose - a muscular pump that moves blood around the body, but in most ways the circulatory system of this insect is a little bizarre.

The principal heart is a muscular tube running down the middle of the fly under the skin. It is closed behind and extends forward through the breast to open behind the head. It has six slits in the abdominal portion, and beats at about 370 times per minute. The blood simply percolates back through the body until it reaches the belly to enter the slits again after several minutes. The blood of the fly carries no oxygen, as red blood cells do in your blood. Flies get their oxygen through a system of tubes connected directly to the atmosphere through 22 small holes along the sides of the fly's body. When you play hard, your heart must pump faster to supply more oxygen to your muscles, but the heart of a fly does not because oxygen flows directly through the other set of tubes.

While the principal heart helps move blood forward, most movement of blood in insects occurs by simply sloshing around in the open system, and sometimes the principal heart beats backwards, moving blood from the front to the back.

Ignore the Awkward: How the Cholesterol Myths are Kept Alive, Uffe Ravnskov PhD, 2010,