Ants in Autumn – Nature Notes
Retired Harvard professor and entomologist Dr. Edward O. Wilson, now 89, is the undisputed world expert on ants. He has spent his entire life studying them and has written and published a long list of books and many scientific articles about his findings. In this Nature Notes essay about these fascinating insects I draw heavily on Wilson’s insights and several other sources in an attempt to summarize what we know about these interesting creatures.
Ants cover the planet in almost unimaginable numbers – a million billion by Wilson’s conservative estimate. They are found everywhere, except in polar cold, but it is in the tropics that ants achieve spectacular diversity. There are 10,000 named species of them worldwide, and likely another 10,000 unnamed ones. Canada has more than 100 species of ants, and there are 93 species in Ontario.
Ants are a complex and fascinating group of insects. In terms of numbers and individuals they are the most abundant six-legged insects on Earth, making up about 10% of the total animal mass. One hectare of rainforest contains more than nine million ants. They dominate a wide range of habitats, including arid deserts, frozen tundra – and kitchen garbage cans. Ants are related to bees and wasps and are completely social insects, dependant on others in their colony for survival. They pass through life in four stages – egg, larva, pupa and adult. They are well adapted for life underground because they are almost entirely blind. Their life is run by chemical smells and tastes.
Ants are generally easy to recognize; their colour is usually black, dark brown, red, or tan. Depending on the species, their size can range from 1 to 13 mm in length, with some exceptions. Like all insects, the body of an ant is divided in three distinct parts: head, thorax and abdomen. The thorax is joined to the abdomen by constricted petioles, also known as nodes. All ants have three pairs of legs used for walking, and they do not have wings, except for the reproductive swarming ants, which have two pairs of functional wings used for mating flights.
Ants are social insects that live in sophisticated societies, colonies with populations often reaching hundreds of thousands. Most ant colonies build nests in soil. Some species, like the carpenter ant, tunnel into wood to create nesting chambers. A colony functions as a single organism, centered about the queen, who is the mother of the colony. Her task is to constantly lay eggs to keep the colony populated. Most colonies have only one queen and will die when she dies, although in some species a colony can have several queens.
Most other colonies’ numbers can vary from 100,000 to 250,000 individuals. A typical ant colony consists of three distinct social castes: the queen, drones, and workers. To establish new colonies, ants undertake nuptial flights: swarms of winged sexual ants depart the nest in search of another location and mate for about 30 minutes. The males die shortly thereafter, along with most of the females. A small percentage of the females survive to initiate new nests. Pharaoh ant workers live only a few weeks. Workers of many other ant species can live up to three years. Most queens live more than five years.
An anthill, in its simplest form, is a pile of earth, sand, pine needles, clay, or a composite of these and other materials that build up at the entrances of the subterranean dwellings of ant colonies. Legions of worker ants carry tiny bits of dirt and pebbles in their mandibles and deposit them near the exit of the colony. They normally deposit the material at the top of a hill to prevent it from sliding back into the colony, but some species sculpt the materials into specific shapes and may create nest chambers within the mound.
Some ant behaviour is truly remarkable. Fire ants build rafts with their bodies to escape floods. Others, again using their bodies, build towers. Ants have no architectural plans, they operate on a few rules, such as “wander aimlessly upward and if you find a non-moving ant, attach yourself to it and become a building block.” They build tower structures on wide rings at the bottom and narrow rings at the top, spreading out the weight so that any individual ant has only to support the weight of three other ants.
Another striking thing about ants is that some of them just sit around doing nothing. Researchers at Georgia Tech studied groups of 30 colour-coded ants digging tunnels. About 30% of them did 70% of the work. Others did very little or nothing. Interestingly, when the researchers removed the hard-working ants, some of the previously less active ants stepped up and began working harder.
Ants are also better traffic engineers than humans. They never run into stop-and-go traffic or gridlock on their trails. If an ant comes across a blockage on the road, it will pick up the obstacle, move it off the road and continue walking, making sure that traffic is not interrupted. There never is a traffic jam. Although the brains of ants are smaller than pinheads, they are engineering their highways and adjusting road traffic. They establish routes from their nests to their foraging areas, then straighten out the roads, maintain them, and create shortcuts. While on the road, they adjust where they go and how fast they go.
One of the key roles that ants display in an ecosystem is dispersing seeds. European fire ants are very good at that, better than native woodland ants. A new study from the University of Toronto suggests that European fire ants are also helping to spread an invasive plant, the greater celandine.
Most ant species found in Canada are omnivorous, feeding on a wide range of food sources. The dietary requirements of ants change throughout the year, depending on the season and needs of the colony. During mating season, from spring and into the summer, the colony requires ample protein to facilitate the development of the maturing larvae. Consequently, the ants forage for food high in protein, including preying on other arthropods and small invertebrates during this time of the year. As the summer continues, the colony begins to focus on preparing the nest for winter or relocating to a suitable overwintering site. Due to the energy needed to perform such tasks, ants switch from a protein-based diet to one primarily consisting of carbohydrates. The varied diet of ants regularly includes fungi, plants and organic matter, seeds, and a wide range of food items stored and consumed by humans, as well.
Common structure-infesting ant species found in Canada include the black carpenter ant, pavement ant, pharaoh ant, odorous house ant, Argentine ant, and thief ant. Pavement ants, depending on the location of nests, can be a bit of a nuisance, especially if nesting indoors. Reddish pharaoh ants are another indoor nuisance pest, often attracted to foods high in protein and sugar. They commonly nest in small cavities inside furniture or behind baseboards. Carpenter ants build colonies of 3,000 or more. They are drawn to damp areas, easy-to-chew wood, often around window sills and door frames.
Controlling ant predators of crops or pests in a home is a daunting challenge. Despite the vulnerability to cold (these insects do not thrive in temperatures below 20 degree Celsius) ants are remarkably hardy. Some can survive flooding. One species can live up to 14 days submerged in water!
Peaceful ant colonies flourish at a greater rate than warring colonies. By studying pairs of colonies, scientists observed that after 70 days, non-aggressive colony pairs had significantly higher population numbers than combating colony pairs. Ants thrive as a cooperative female society. Perhaps these are messages we should think about.
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Sources: Canadian Wildlife Federation, Ontario Nature, Wild City (Bennet & Tiner), The Green Book (Gahbauer), E.O. Wilson, articles and personal filed notes.
Nature Notes are posted as blogs on the website of Nature Canada.
Earlier editions are archived on the websites of the Rouge Valley Conservation Centre and of the Rouge Valley Naturalists.