Reading 1

Unit 10- Reading 1

Page 146

Attack of the Fire Ants

The red fire ant, Solenopsis invicta, is one of over eighty thousand species of ants worldwide. Like their close relatives, the bees, many species of ant have a sharp appendage, called a stinger, at the end of their body. Most bees can sting only once, and then they die. An ant’s stinger can be used repeatedly.

The red fire ant is not native to North America. It arrived on ships from South America in the 1930s through the port of Mobile, Alabama. That landing in Alabama initiated a full-scale invasion. Since then, fire ants from this is invasion have spread throughout the southern United States and Puerto Rico. The ants have also made their way to Australia, New Zealand, and China.

ANT ZONES

Following World War II, circumstances in the 20 U.S. worked in the ants’ favor. The fire ant is known as a “tramp” or “weed species because it thrives (like a weed) in recently cleared or disturbed areas. After the war there was rapid population growth in the “Sunbelt” of America’s south and southwest. Land cleared for new homes, parks, and factories was a perfect habitat for fire ants. Now, similar conditions in rapidly developing areas of Asia may prove inviting to the ants.

By 1950, the ants in the U.S. had made it halfway up the border between Mississippi and Alabama. Since then, they have become firmly established in Texas, and they are relatively common in Arizona. A few have shown up in California. They may eventually move into some milder parts of Oregon and Washington. Public health experts estimate that, in any given year, from 30 to 60 percent of people living in Solenopsis zones in the United States are stung.

The ant grasps the skin with its tiny, powerful jaws, arches its body, injects the stinger into the skin, and releases venom. If not stopped, the ant will rotate itself around and create a whole circle of stings. There’s an immediate burning sensation, followed by hours to days of intense itching. Virtually everyone who is stung by a fire ant develops a red welt that stays painful for several days. Up to half of the victims will experience larger reactions near the location of the bite.

SERIOUS REACTIONS

Fire ant venom may be toxic to the nervous system. One tree cutter in Florida suffered serious fire ant attacks three times within one year. After the third attack, his right hand and forearm became numb and his wrist became weak. This condition lasted for about a month. The venom is also necrotic-it kills the tissue that it comes in contact with. If this necrosis, or tissue death, happens after a sting, permanent scars may remain on a victim’s skin. Terrible sores can result if an infection takes hold near the necrotic tissue. The most dangerous physical response to a Solenopsis sting, however, is an anaphylactic reaction. This is the same kind of reaction some people have to bee stings and is similar to an extreme allergy. It begins with weakness, itching, chest tightness, and wheezing? This can bring on a sharp fall in blood pressure and sometimes even death. In some fire-ant zones, fire ant venom causes more fatal reactions than bee stings. In sensitive people, a single sting is usually enough to initiate the reaction.

Fire ant venom is a watery solution of toxin that affects human mast cells. These cells are filled with a chemical called “histamine.” Histamine is the same chemical that triggers the sneezing, itching, and other symptoms of an allergy.

When an allergy-causing substance > enters the body, the walls of the mast cells weaken until they can no longer contain the histamine. The cell explodes, releasing a rush of histamine. If these histamine explosions occur in the lungs, the reaction can be serious perhaps including a blockage of the passages that deliver air to the lungs. These lung problems are not common, but they are a real threat to anyone extremely sensitive to fire-ant venom.

Nothing can completely neutralize the effects of fire-ant venom, but people sensitive to it who live in fire-ant territory have some treatment choices.

Immunotherapy is currently the best option for minimalizing reactions. It consists of a series of injections, administered on a regular schedule. At first, patients receive very small amounts of fire-ant venom that their bodies can tolerate. With each injection, the amount of venom is increased, which causes the person’s body to start building up resistance to it. Eventually, patients have sufficient defenses to tolerate a fire-ant sting.

The immunotherapy regime is expensive, and it also requires a long-term commitment. Doctors estimate that treatments will take as long as two years.

TEMPERATURE BOUNDARIES

Fire ant populations have not yet established themselves very far north. Many, many studies have tried to discover which temperatures are too cold for them. In summary, research shows that, like any insect, a fire ant becomes less active as the weather grows colder.

Eventually, it becomes totally motionless. Fire ants hit this temperature boundary at about 50° Fahrenheit (10° Celsius). Above that temperature, ants are active. Below it, the ants slow down and can barely move.

In places where temperatures stay at least this low for much of the year, ant colonies cannot survive outdoors. In the U.S., at least for the moment, this keeps the fire ants from attacking areas east of the Pacific Coast mountain ranges and north of the Ohio River.

Worldwide, Solenopsis ranges as far south as the southern tips of South America, Africa, and Australia. In the Northern Hemisphere, it does not generally spread north of 30 degrees north latitude and cannot survive north of 45 degrees north latitude.

These statements, however, are based on climate conditions in the early 21st century. What if the climate changes? Some health officials worry that global warming may open the door for the ant armies to march farther north.

A more immediate worry is that ant colonies may take hold inside heated buildings. Under these circumstances, external temperatures would make no difference at all, and fire ants would become a much bigger problem for humans.