What is this strange looking brownish-disc like thing floating on the water in the image below? Floating algae? Frogs' eggs? A big brown cookie? Truth be told, you already knew that whenever this type of question is asked, the answer is some absurb truth that you could never imagine possible.
photo: http://bugguide.net/node/view/30113/bgpage?take2
Red Imported Fire Ants (scientific name: Solenopsis invicta), or simply RIFA, is one of the 280 species of ants in the world. Although it is native to South American, it is common in the United States, Australia, Taiwan and other South Asian countries as well. The bodies of these fire ants, like all insects, consist of 3 parts - the head, the thorax and the abdomen. They also have 3 pairs of legs, and 1 pair of antennae. RIFA are more aggressive than most ants species, and have been known to "kill newborn calves if the calves do not get on their feet quickly enough. They attack en masse, responding to pheromones that are released by the first ant to attack. They then swarm and immediately sting when any movement is sensed."1
They nest near moist areas, like rivers and ponds, and their nest is usually not visible as it will be hidden under logs, rocks and bricks. Unlike other species of ants which bite to inflict a deadly wound, these fire ants bite to get a grip, then sting their prey by injecting a toxic venom, the sensation of which is "similar to what one feels when burned by fire"2.
photo: http://entomology.lsu.edu/faculty/hooper_files/RedImportedFireAnt.jpg
RIFA are able to survive floods by clinging together to form rafts. They have adaptations to contend with both flooding and drought conditions. Their nest structure includes a network of underground foraging tunnels that extends down to underground water supplies, ensuring a steady supply of food and water in winter. The more intriguing behaviour exhibits in times of increased water levels; these ants will gather and begin to form a huge raft, with the queen on the inside. The raft will flow with the current until the floodwaters recede, then they will get on to anything that they come into contact with to build their new nest. If the raft hits a solid object, the ants would swarm onto it and wait for the water level to fall.
photo: http://www.tarleton.edu/~physci/Envir/FireAnts.jpg
These scary little buggers have honed survival skills. They are able to avoid drowning while rafting by "rotating from the underwater side to the above water side with the queen staying in the middle. Enough air bubbles adhere to their spiracles that they have no problem being underwater for a period of a couple minutes"3
Also, as a precautionary measure, "colonies would compensate for their elevated vulnerability by increasing their defensiveness"4 through adjusting the amount of venom that they delivered per sting. As the ants are more susceptible to predatory attacks while rafting, they have to protect themselves by increasing venom doses in the event of an attack. Any encounters with an ant-raft would be potentionally more dangerous than if on land.
(for a more detailed explanation of the experiment, please refer to K.L. Haight's research article, 2006, an abstract of which can be found here)
photo: http://www.angryflower.com/ants.gif
Citations:
(1) http://en.wikipedia.org/wiki/Red_imported_fire_ant
(2) http://en.wikipedia.org/wiki/Fire_ants
(3) http://bugguide.net/node/view/30113/bgpage?take2
(4) Haight K.L., 2006. Defensiveness of the fire ant, Solenopsis invicta, is increased during colony rafting. Insectes Sociaux (Vol. 53, No. 1, Pg. 32-36)
References:
1. http://www.springerlink.com/content/x362362m5708212v/
2. http://www.chron.com/disp/story.mpl/storm2001/943267.html
3. http://bugguide.net/node/view/30113/bgpage?take2
4. http://en.wikipedia.org/wiki/Ant
5. http://en.wikipedia.org/wiki/Fire_ants
6. http://en.wikipedia.org/wiki/Spiracle
7. http://www.independent.co.uk/news/science/wild-things-the-weirdest-facts-from-the-animal-kingdom-418659.html