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Taxononomy
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Formicinae
Genus: Formica
Species: Formica obscuripes
Life cycle
Eggs of Formica obscurpies also known as the Western Thatching Ants are typically laid from April to as late as middle of August. Eggs are laid in brood chambers and will hatch anywhere between 23 to 53 days. Formica obscurpies is holometabolous meaning it will through a complete metamorphosis before becoming an adult. Once hatched, larvae will begin to pupate after 7 to 33 days and will remain as a pupae for 31 to 91 days before reaching adulthood bringing the total time it takes for the western Thatching Ant to develop from egg to adult to 61 to 122 day. Western Thatching Ants are omnivores feeding on both plant matter such as leaves, nectar, etc, and many other insect species such as grasshoppers, flies, and even other ants. Western Thatching Ants are also known scavengers which means they will feed on dead insects as well as other small invertebrates often times the foraging ants of the colony will bring insects both living and dead back to the nest where it will later be consumed.
Habitat and Distribution
Western thatching ants are native to North America and are found all across the western half of the US and Canada. Western Thatching ants prefer a more dry climate such as dry grasslands and are often found in areas of secondary succession. The mounds built by these ants are quit distinct. The height of the mound ranges from 1-18 inches and can go as far as 4 feet into the ground. Mound height is usually associated with the colonies age and health. Mounds are
typically built in areas with minimal foliage coverage in order to expose the mound to Sunlight. The mound are built of a material called Thatch, which is where the Western Thatching ant receives it's name. Thatch is made up of twigs, grasses, plant parts, and soil. The thatch acts a temperature regulator for the nest helping the ants to survive various temperatures, humidity, and a variety of weather conditionsLife in the Colony
Like all ants Western thatching ants are eusocial which is basically the ultimate level of sociality found in the animal kingdom. Eusociality is defined by the following characteristics:
cooperative brood care
overlapping generations
Division of labor into reproductive
These unique characteristics lead to a high level of relatedness among the colony. The principle of inclusive fitness suggests this level of relatedness is plays huge role in fostering the amount of cooperation seen in the Western Thatching Ant.
The Western thatching ant, like all ants, communicate in a variety of ways such as sound, touch, and the use of pheremones. The use of pheremones is more developed in ants than in other hymenopterans such as bees, wasps, etc. Pheromones are perceived through the ants antennae which provide information as to the direction
and intensity of the scent. Pheromones serve a wide variety of purposes in the ant world such as leaving chemical trail to lead other ants from the colony to a food source. A crushed ant will also emit a chemical that will cause ants receiving the signal to frenzy and attack. Pheromones can also be used to confuse enemy ant into to attacking each other.
Unlike some species of ants the Western Thatching Ant has been known to form what are known as super-colonies. A super colony is when one colony of ants builds multiple nests. One study found a super colony of Western Thatching ants with a total of 210 Nests! Western Thatching Ant super colonies are also polygynous meaning a single colony will have multiple queens for breeding. One colony was recorded as having 198 queens.
Reproduction
Reproduction in the Western Thatching Ant takes place during what is known a nuptial flight. During a nuptial flight both queens from the colony and winged males will take flight in a swarm. The first thing the virgin queens and reproducing males will do is scatter to ensure outcrossing occurs. The queen will then land and release a pheromones to attract males. Males will then attempt to mate with the queen. Often times the queen will attempt to escaped the male thus ensuring only the strongest and fastest male mate.
A queen will typically mate with multiple males during a nuptial flight. From there the queen will store the sperm in a special organ call a spermatheca. Because this sperm is stored in the queen's spermatheca the queen will only need to mate once as the stored sperm can be used to fertilize a queens eggs throughout it's lifetime.
After a nuptial flight some queens will return to an established nest while others will attempt to form new colonies. To do this the Formica obscuripes will enter the nest of a different species of ant from the Formica fusca group. The workers of the invaded nest will accept the new queen while the original is either killed or driven off. The Western thatching ant will then lay eggs which are cared for by the F. fusca workers. Eventually all the is left is are the Western Thatch Ants as the host workers will eventually die off
Associations with other species
Perhaps one of the most fascinating aspects of the Western Thatching Ant is the relationships they have formed with other species of insect throughout the ages. Perhaps the best example of this is the mutualistic relationship between The Western Thatching ant and several species of aphid. To Western Thatching Ant collection of honey dew is crucial to their survival. Aphids are actually known to excrete honey dew. Over thousands years of evolution Western Thatching ants as well as several other ant species have learned to
harvest this honey dew from the aphid's anus. This relationship is so well developed that aphids will only excrete honey dew when an ant drums on the aphids body with it's antennae.
The excretion of honey dew is costly for the aphid energy wise. However in exchange for this honey dew the ant provides the aphid with a variety of services such as protecting them from predators, feeding them, etc. Western Thatching ants will even construct special chambers within their tunnels where they will carry aphids and provide for them within the nest. This practice of "aphid farming" is just one of the relationships these ants have with other species. Western Thatching Ants' nests also house a variety of insects who use the ant tunnels for shelter and even to hibernate for the winter. Certain crickets have even learned to imitate the Western Thatching Ant's antennae, tricking the usually hostile ants into thinking the cricket is just another fellow ant.
Citation
Conway, J. 1996. A field study of the nesting ecology of the thatching ant, Formica obscuripes Forel, at high altitude in Colorado. Great Basin Naturalist, 56/4: 326-332.
Conway, J. 1997. Foraging activity, trails, food sources, and predators of Formica obscuripes Forel (Hymenoptera:Formicidae) at high altitude in Colorado. Pan-Pacific Entomologist, 73/3: 172-183.
Crutsinger, G., N. Sanders. 2005. Aphid-Tending Ants Affect Secondary Users in Leaf Shelters and Rates of Herbivory on Salix hookeriana in a Coastal Dune Habitat. American Midland Naturalist, 154/2: 296-304.
McIver, J., K. Yandell. 1998. Honeydew harvest in the western thatching ant (Hymenoptera: Formicidae). American Entomologist, 44/1: 30-35.
“Species Formica Obscuripes - Thatching Ant.” Species Formica Obscuripes - Thatching Ant - BugGuide.Net, Bugguide, bugguide.net/node/view/31269.
Web, Animal Diversity. “Critter Catalog.” BioKIDS - Kids' Inquiry of Diverse Species, Formica Obscuripes, Western Thatching Ant: INFORMATION, BioKIDS, www.biokids.umich.edu/critters/Formica_obscuripes/.
Weber, N. 1935. The Biology of the Thatching Ant, Formica rufa obscuripes Forel, in North Dakota. Ecological Monographs, 5/2: 165-205.
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