How does thermoregulation work in ants? (Farzaneh)

Dear AntAsk,

I was wondering how thermoregulation works in ants?

Thanks in advance!

Dear Farzaneh,

This is actually a great question! We have forwarded your question to Clint Penick (photo of Clint with a large wood ant thatch mount at the end of this post), who has studied thermoregulation in some ant species. Here is his response:

"Ants are ectotherms (or "cold-blooded"), which means that they rely on their environment for thermoregulation. This can be seen in their nest structure. Ants usually construct deep, underground nests that maintain fairly stable temperatures. In the summer, ground temperatures provide shelter from the heat, and in the winter the ground is warmer than the outside air. The winter ant, Prenolepis imparis, builds some of the deepest nests known to ants (close to 12 feet or 3.6 meters below the surface), and these ants retreat to the cool shelter of their nests during the summer and only come to the surface during cooler months.

Many ants build their nests under rocks, which can serve as solar collectors. This is why ant researchers are sometimes called "rock flippers," because many species of ants can be found under rocks, especially in the morning when these rocks begin to heat up. Because rocks often stick above the ground surface, they have a lower specific heat than the surrounding ground. This means that they will heat up faster during the day-even under shady conditions-but they also cool down faster at night.

Some ants have developed special nest structures that aid in thermoregulation. These ants are the "mound builders." The fire ant, Solenopsis invicta, builds a mound out of soil, which is riddled with a spongiform network of tunnels. These mounds serve the same function as rocks-they collect solar thermal energy and have a reduced specific heat so they heat up faster than the ground. Fire ant larvae grow best at 32ÂșC, so workers move their larvae up to the surface of the mound early in the morning as the mound begins to heat up. By mid day, the surface of the mound is too hot, so the ants move the larvae deeper into the nest to track the optimal temperature. By nightfall, all of the larvae and most of the colony is located deep underground where temperatures are more stable. In fact, this behavior is so reliable it can be used as a natural compass: the ants bring all their larvae to the south side of the nest in the morning, where the sun's rays are the strongest. To see an example of a mound nest of the fire ant, check out this previous post here.

The species that build the largest mounds, however, use a completely different process. These ants, which are called "thatch builders," live in northern Europe and Scandinavia. Thatch mounds can be over two meter tall and are built out of decaying pine needles and leaves. Like a compost pile, the leaves of the mound release heat as they decompose, and this plant material also provides insulation. While fire ant mounds reach their highest temperatures on the outer surface, thatch mounds are warmest near the center of the mound where the heat from decomposition is the strongest. In addition to the mounds, thatch ants also use their own bodies to heat the interior of their nests. Worker ants sun themselves on the surface of the mound and then quickly run inside to heat up the interior of their nest with their warm bodies. To see an example of a thatch nest of a wood ant, check out this previous post here.

Solar collector vs thatch mound.png

Figure courtesy Clint Penick

Other insects, like honey bees, can generate internal body heat by flexing their flight muscles. Ants don't have flight muscles, but their bodies do produce a limited amount of heat. Army ants, like Eciton burchelli, don't dig nests in soil, but instead construct hanging bivouacs out of their own bodies. They are able to use the collective heat of their bodies to keep warm over night, and they can adjust their position to allow ventilation during the day.

Honey bees can also ventilate their nests by using their wings like fans. Again, ants don't have wings, so they use different methods for nest ventilation. The massive colonies of Atta fungus-gardening ants are topped with a dome of soil that has small chimneys. As winds blow over the nest, convection over the chimneys pulls stagnant air out of the nest and allows fresh air to flow back inside. This has a negligible effect of nest temperature, but it does help cycle CO2 out of the nest and increase oxygen levels inside."

Atta nest ventilation.png

Figure courtesy Clint Penick

Clint Penick (guest expert), Steffi Kautz & the AntAsk Team

Formica mound-1.jpg

Guest expert, Clint Penick, with a Formica polyctena thatch mound in northern Estonia

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