Page 132 - Engineering in Nature

Engineering in Nature

The vein leaving the abdominal region enters the thorax, where
the thoracic heat exchanger is. The vein enters the thorax under the
stomach, then immediately climbs to the upper part of the thorax—in
other words to the back. Here it makes a sharp U-turn and heads back
under the thorax. Here, the shape of the vein may be compared to a
letter N whose arms are touching. The part of the thorax that contains
this bend in the vein is the heat exchanger. Since the two arms form-
ing the bend in the vein are very close to one another, the temperature
difference between them is reduced to a minimum. Thus the temper-
ature in the moth's thorax is perfectly stabilized.

The Vein System in Winter Moths
To better understand the importance of the thoracic heat exchan-
ger, it's useful to compare the winter moth's vein system with that of
the sphinx moth, which lives in warmer environments.
Sphinx moths have relatively larger bodies than winter moths and
live particularly in tropical regions. Instead of a heat exchanger, these
insects have a cooling system in their thoraces. Instead of the N-like
bend in the vein, the sphinx has one more resembling a small letter r.
As can be seen from the diagram overleaf, the left side of the vein
bend is longer in the sphinx moth than that in the winter moth. This
leads to a temperature difference between the left and right arms of
the bend, and for that reason, this part of the sphinx moth's circula-
tory system is known as its cooling mechanism.
Both sphinx and giant silk moths have a mass 60 times greater than
that of winter moths. Therefore, one might expect that they are heated
more easily. But contrary to what one might imagine, these moths
transmit excess heat first to the head and abdominal region and from
there to the air. To state it another way, sphinx moths' cooling system
corresponds to the heating mechanism in winter moths. If winter

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