Society

Forget fire ants, leaf cutter ants hardest to control

In my front yard I have one sandy spot riddled with mounds built by the Texas Leaf Cutting Ant (Atta texana).

Known as the "town ant", "cut ant", or "parasol ant" - so named because of the way they carry leaves over their heads - the Texas Leaf Cutting Ant lives in Texas and Louisiana, and parts of northern Mexico. About 40 species of leaf cutting ant live further south in Central and South America.

These ants live in sandy or loamy soils, preferably in open areas near brush or forest. They are a dark-brown color. The workers are 1/16 to 1 .2 inch long with three pairs of spines on their back and one pair on the head.

Their mounds appear overnight, and are indeed towns. There are at least 40 cratershaped mounds in my yard. Each mound has a single entrance hole. The colony is young, as the mound height fits that of a younger colony - 5 to 14 inches high. Older mounds get up to 3 feet high. I've found multiple "feeder holes" the ants use during foraging. These openings also serve as ventilation shafts, as the huge, heavily populated nests cause carbon dioxide build up.

Nests can cover 3,000 to 4,500 square feet, with a depth of 8 to 15 feet. About 8 million ants can occupy it. Some nests have survived past one hundred years.

The ants are the only animal besides us, termites, and ambrosia beetles that farm. They turn the plant material they collect into a pulp which grows a fungus that they eat, although adults will partake in plant sap. To keep their food disease and pest-free, the ants use antibodies from a bacteria grown on their skin, as well as physically removing it.

Colonies must contend with waste from fungus cultivation. Some worker ants specialize in either transporting waste to a waste heap, or working the waste heap like we work compost piles.

The ants can detect chemical signals from their fungus that tells them if a leaf is toxic. If it is, they stop collecting that leaf. Otherwise, pretty much any plant is open season for harvesting.

Foraging occurs at night during the summer. Fall and spring they come out during the day. They are inactive on cold or cloudy days.

An established colony, with up to five queens, can be hard to control. However, less than 10 percent of new colonies make it past three months. Queens fall prey to birds, armadillos, rodents, and other ants. Other factors include failure of the fungus garden due to disease or not enough

nutrition.

Mating occurs in April and May, usually after a heavy rain. The queen mates with several males, who subsequently die. She starts a colony using bits of fungus stored in her mouth, which she cultivates, and lays her first eggs.

Leaf cutters move into areas that have been disturbed by humans. This occurred at my house, where the site had been cleared for building. I believe that once we get the environment more balanced - native grass and plants - they will move away from our home. I have found they won't bother rosemary, lavender, or tomato plants. Everything else, including lantana and salvia, is fair game.

A colony can consume as much leaf matter in a day as a full grown cow. The total yearly agricultural loss from Leaf cutter infestation in Texas and Louisiana runs close to $5 million.

Controlling these ants is difficult since they won't eat ant bait. Organic methods include garlic, vinegar, Pyrethrum, or Diatomaceous earth.

Chemical controls include Amdro Ant Block, or other insect dusts. These cannot be used where food plants are grown.

walton.shawn@gmail.com

El Camino Real Master Naturalists:

grovesite.com/tmn/ecrmn


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2009-10-29 digital edition



The burn ban for Milam County has been lifted. Burning is always prohibited in the county's municipalities.


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