A bee needs to dissipate heat in two main situations: when blood is flowing to through the aorta in the thorax and when it is incubating its brood. For these reasons a bee has two unique features which aid heat dissipation in these situations.

The aorta makes a hairpin loop as it runs from the petiole to the flight muscles in the thorax. This structure gives the aorta a larger surface area through which heat can be exchanged. Heat moves from the warm blood into the flight muscle that needs to be warmed to at least 30 degrees C (Heinrich, 1976).

When a bee incubates its brood it transfers heat from its abdomen to the brood in the hive. In order to speed this process, bees lack the hair on the lower surface of their abdomens. Hair covers a bee's body everywhere else to aid insulation. Since the abdomen does not need heat, the excess warmth is conducted through the hairless bottom of the abdomen directly to the brood (Heinrich, 1976).

Dissipating heat in both the aorta of the thorax and in abdomen would be severely retarded without these morphological advantages that facilitate the passage of heat.

BUT, the quick passage of heat is not desirable in all processes that occur in bees. Sometimes a bee needs to retain heat. A bee's body has morphological characteristics that are designed to conserve heat where necessary -- mostly in the thorax. What are these characteristics?

An insulating layer of pile covers the entire thorax. This is an important feature because any heat that the thorax can retain results in less work required of the flight muscles to reach the 30 degrees C that is necessary for takeoff (Heinrich, 1976).

Air sacs are located in the anterior region of the abdomen. The air sacs act as a buffer between the thorax and abdomen, slowing the leakage of heat from the thorax to the abdomen (Heinrich, 1976). This is beneficial because the thorax needs the heat for the flight muscles whereas the abdomen has no use for it.

The aorta and the venial blood flow in opposite directions next to each other as they pass through the petiole forming a counter- current heat exchange. This conserves the heat of the thorax by transferring the heat from the venial blood to the arterial blood which is flowing into the thorax to the flight muscles. Without the countercurrent heat exchange the flight muscles would be cooled down by the arterial blood entering the thorax from the cooler abdomen and valuable heat from the thorax would be dumped wastefully into the abdomen (Heinrich, 1976). Then the flight muscles would have to work even harder to counteract this heat loss.

 

diagram adapted from Heinrich, 1976