Have you ever wondered why ant nests look the way they do? Why have a dome-shaped nest, well within sight of enemies and exposed to grim weather? It’s all about the controlling of climate and temperature.
An important factor in the success of an ant colony is its ability to regulate climate and temperature. Ants love heat and they often go to great lengths to achieve higher temperatures. But there are also species that work towards lowering it, often situated in very warm environments.
Most ants do not, unlike the popular belief, live in anthills. Only 16 of the 81 Scandinavian species build domes out of forest materials, like the classic woodland ants. Globally that number is even lower. It is much more common that ants settles right in the ground, preferring the materials of dirt, sand, moss or rotten wood (for example stubs).
Climate and Temperature in Classic Anthills
The gigantic anthills made out of forest materials such as twigs and needles are incredible constructions, protecting the ants from the outside as well as preserving temperature and moist inside. The roof is impenetrable to weather and wind, and have lots of small holes that can be opened and close to regulate temperature. (1) The idea of a large dome is simple: the more surface area that is exposed to the sun, the more heat it will generate. And this is great for ants, considering their brood and queens love warmth.
The construction of a classic anthill of the species Formica polyctena is a symmetric dome made out of twigs, needles, leaves, small rocks, resin and pieces of charcoal. Underneath the surface there is dirt and a lot of tunnels and chambers. The nest is heated by the sun, but also by the metabolism of the ants themselves. When the outside temperature is as low as 13°C, a 30 centimeters tall anthill can still parade 25°C on the inside. This is a combination of a well-built nest together with a high worker-density in the core of the colony. This way the ants can preserve warmth and energy from the sun, giving their brood a boost to their development in a perfect environment. (2)
Other Ways of Controlling Climate and Temperature
In northern Florida the species Prenolepis imparis found their colonies in a mixture of dirt and sand, and have a completely different way of regulating the climate of the nest. They dig one long tunnel straight into the ground, 2,5-3,6 meters down, and constructs the nest at the end of it. No chamber is built higher up than 60 centimetres from the surface, and most are situated in the lower half of the tunnel. This way colonies an guarantee a stable temperature all year round, since the climate and temperature of the soil don’t vary much in this area. For Prenolepis this way of life is incredibly important because they can’t handle the warm summers of the Florida area. Their nest is a clear strategy towards handling this, and they will thereby always be able to keep temperatures between 16°C and 24°C. Species of desert ants often use the same technique to get away from the heat, since a few seconds of the Sahara sun can kill an ant.
Ants in temperate climate zones are, in comparison, all about preserving heat. They need it to survive, and especially during the start of the ant year. Some species, like Lasius niger, prefers to centre their nest around stones. This is no coincidence, but a well-thought-out strategy. The stones generates a lot of heat – a flat and thin stone near the surface is therefore optimal for these black garden ants. When placed under one of these stones, the colony can quickly get its egglaying and brood-development going when the first rays of spring start to shine. This is an important head start in a competitive insect world. The properties of heat absorbing is shared with rotten wood and bark, making them suitable choices for some species. Since wood don’t attract as much heat as stones, the species digging through them and settling down are less sensitive to the need of heat and humidity. (3)
With a well-planned nest the workers can move the brood around, depending on season and weather, to achieve optimal environments. They are mostly kept in the warmest areas of the nest, preferring temperatures of 25°-35°C. The pupae is stored in the dry regions. If the nest is built under stones or wood, the brood is kept there to absorb the heat. When the temperature outside declines the workers move the brood to the centre of the nest to keep it warm. (4)
1. Per Douwes, Johan Abenius, Björn Cederberg, Urban Wahlstedt (2012) Nationalnyckeln “Steklar: Myror-getingar. Hymenoptera: Formicidae-Vespidae” p. 39 (Swedish)
2. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 373
3. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 371
4. Bert Holldobler & Edward O. Wilson (1990) “The Ants” p. 372
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