Formic Acid Dangers and Uses in Nature and in Humans
An Interesting and Useful Chemical
Formic acid is an irritating chemical present in the sprayed venom of some ant species and in the secretion released from some stinging nettles. It's dangerous at high concentrations, but at low concentrations it's very useful. Humans use formic acid as a food preservative, since it's an antibacterial substance. It’s also used to treat pests, to produce food and cosmetic additives and to help a variety of industrial processes to occur.
Our bodies make small quantities of formic acid from the methanol that we ingest, inhale or produce. Some of the methanol produced in the body is made from aspartame. The body converts aspartame into aspartic acid, phenylalanine and methanol. The methanol is then converted into formic acid. Researchers say that the formic acid in our body is generally too dilute to be dangerous, however.
Formic Acid Structure and Properties
Formic acid is the simplest member of the carboxylic acid family and is also known as methanoic acid. Its molecular formula is HCOOH. The molecule is composed of a carboxyl group (COOH) with a hydrogen atom attached. In the carboxyl group the carbon atom has a double bond joining it to the oxygen atom and a single bond joining it to the hydroxyl (OH) group.
Formic acid can be made synthetically in laboratories. In nature it usually exists in the form of a colorless liquid. This liquid freezes at 8.3 degrees Celsius (46.9 degrees Fahrenheit) and boils at 100.7 degrees Celsius. (213.3 degrees Fahrenheit). It has a strong odor and is often described as having a "pungent" smell.
Formic Acid in Ants
Formic acid got its name from “formica”, the Latin name for ant. An English naturalist named John Ray was the first person to isolate an acid from ants. In 1671 he distilled the crushed bodies of dead ants to extract the acid, which was eventually named formic acid.
Ants bite to protect themselves or to attack other creatures. They grab hold of their victim with their mandibles (jaws). Some ant species then sting the victim. The stinger is located at the tip of the abdomen and injects a toxic secretion. Instead of stinging, certain species of ants release a spray of venom from the end of their abdomens. This venom contains formic acid. Some ants bite but do not sting or spray toxic chemicals.
Members of the ant subfamily known as the Formicinae have an opening at the tip of their abdomen called an acidopore in place of a stinger. The acidopore releases a spray of formic acid from the ant's venom gland when necessary. Wood ants, yellow crazy ants and tawny crazy ants all belong to the Formicinae subfamily.
Thousands of Wood Ants Spray Formic Acid
Yellow Crazy Ants
Yellow crazy ants (Anoplolepis gracilipes) are invasive and very destructive insects. They neither bite nor sting, but they do spray formic acid to subdue their victims. The ants are yellow-brown in color and have long legs and antennae. They're known for behaving frantically when they're disturbed.
Yellow crazy ants are versatile creatures. They eat a wide variety of animal tissue as well as honeydew secreted by aphids and other insects. The ants are classified as predatory scavengers. A very worrying aspect of their lives is the ability to form huge supercolonies which have hundreds of queens.
The ants have caused some very serious damage to the populations of some animals, including the red crabs on Christmas Island and seabirds in Hawaii. They also interfere with human lives. Sometimes the ant population releases so much formic acid into the air around their nest that breathing becomes painful. Skin and eye contact with the acid is also painful.
Yellow Crazy Ants, Formic Acid and Hawaiian Seabirds
Like the yellow crazy ant, the tawny crazy ant releases a spray of formic acid as a chemical weapon. It also rubs its formic acid secretion over its body. The covering of acid protects it from the venom of the red imported fire ant. How this protection works is unknown.
Tawny Crazy Ants Detoxify Venom of Fire Ants
Fire Ants and Tawny Crazy Ants
The stinging venom of red imported fire ants (Solenopsis invicuta) contains alkaloids and some proteins but no formic acid. A fire ant bites to grab hold of a person's skin, then tucks its abdomen under its body so that the stinger can reach the skin and inject its chemicals. The fire ant then withdraws its stinger, rotates a short distance and stings again, repeating the process until it has formed a circle of stings.
Like the red imported fire ant, tawny crazy ants (Nylanderia fulva) were introduced to the United States from South America. The two species can be found in the same habitats. Researchers at the University of Texas have discovered an interesting phenomenon in relation to the ants. When a crazy ant is stung by a fire ant, the crazy ant curls its abdomen upwards to its mouth, secretes formic acid from its venom gland and then rubs the secretion over its body. The process is shown in the video above.
Although the research team doesn't know how the formic acid protects the crazy ant, they suggest that it may denature fire ant enzymes required for the alkaloid in the venom to penetrate cells.
Formic Acid in Stinging Nettles
The leaves and stems of stinging nettles are covered with hollow, stinging hairs which have walls made of silica. When the hairs are touched, the tip comes off, exposing a needle-like structure which is attached to a venom sac at the base of the hair. The needle then injects the venom into the victim’s skin.
The poison of many stinging nettles contains formic acid, although scientists have discovered that other chemicals are also present. These probably contribute to the painful sting. The additional chemicals include acetylcholine, serotonin and histamine. Histamine is the substance that is released into our bloodstream from mast cells during an allergic reaction. Histamine causes inflammation, swelling and redness. The stinging hairs of some nettles contain oxalic acid and tartaric acid instead of a mixture containing formic acid.
Formic Acid Uses
Since formic acid is an antibacterial agent, it's frequently added to the feed of farm animals to prevent the growth of bacteria. It's occasionally used as a preservative in human foods. Formic acid is also used to create artificial flavors for foods and drinks and artificial scents for perfumes. In addition, formic acid is used in leather tanning, in the processing of textiles and paper and in the conversion of latex from the rubber tree into rubber.
Some birds place living ants amongst their feathers, a behavior known as anting. The ants are very often - but not always - members of the subfamily Formicinae. Scientists don't yet know why birds ant. According to one theory, the formic acid that the ants release kills mites that are attacking the bird’s skin. Humans use formic acid for a similar purpose. Formic acid preparations are used to kill varroa and tracheal mites which invade honeybee hives and attack the bees.
Biology of Varroa Mites
Bee venom is a complex mixture of many chemicals. Some sources claim that the venom contains formic acid, but the latest research indicates that neither bee nor wasp venom contains formic acid.
Dangers of Formic Acid
The dangers of formic acid depend on its concentration. At higher concentrations formic acid is corrosive, has a strong smell and produces dangerous fumes. It produces burns and blisters on the skin and injures the eyes and the mucous membranes in the mouth, throat and respiratory system. Inhaling concentrated formic acid makes breathing difficult. Swallowing the concentrated acid causes severe ulcers (sores) to appear in the digestive tract as well as pain and nausea. Prolonged exposure to formic acid may produce liver or kidney damage.
Formic Acid Production from Methanol
Methanol is made inside our bodies from normal metabolic processes. It also enters the body from fruits and vegetables and their juices. In addition, humans produce methanol as well as aspartic acid and phenylalanine from the breakdown of aspartame, an artificial sweetener. Methanol is toxic, but most of us don't encounter enough of the chemical to be harmed.
Inside our bodies methanol is converted to formaldehyde, which is classified as a probable human carcinogen (cancer causer). However, the formaldehyde is rapidly transformed into formic acid and doesn’t collect in the body. The formic acid then leaves the body in urine or is changed into carbon dioxide and water.
Scientists say that the production of formic acid from methanol in humans only becomes a problem if there is a large amount of methanol in the body, as there would be in methanol poisoning. In this situation, enough formic acid could be made to create a condition called acidosis. Symptoms of acidosis include vision problems, blindness, memory loss, confusion, seizures, coma, low blood pressure and cardiac arrest.
Methanol Production from Aspartame
We can’t avoid the normal creation of methanol in our bodies or its entry into the body from healthy foods such as fruits and vegetables, which should be part of our diet. We can control whether we want to add to the methanol load by ingesting foods or drinks sweetened by aspartame.
The use of aspartame is controversial. However, health agencies say that a person’s normal exposure to methanol, including the methanol produced from aspartame, is too low to cause health problems. They also say that aspartame is safe, provided the Acceptable Daily Intake (ADI) of 40 mg/kg body weight is not exceeded. There are claims that aspartame makes the symptoms of certain health disorders worse, but at the moment there is no scientific evidence to support these claims.
There is one situation in which aspartame is known to be harmful. Aspartame should not be consumed by people suffering from a genetic disorder called phenylketonuria. A person suffering from this disorder is unable to create the enzyme that changes phenylalanine into tyrosine. As a result, phenylalanine accumulates in the body. People with phenylketonuria must follow a low phenylalanine diet to avoid brain damage. Since aspartame breakdown produces phenylalanine, the sweetener must be avoided.
Formic Acid in Space
Scientists think that formic acid may have played a role in the origin of life on Earth. The acid was first found in interstellar space in 1970 and has been found in meteorites that have reached Earth from space. Formic acid has a relatively simple structure and may have been involved in the formation of the more complicated amino acid and nucleic acid molecules found in living things.
Amino acids are the building blocks of the proteins inside living things. Nucleic acids are the building blocks of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). The DNA contains genetic instructions for making our bodies and for controlling its functions. It's located in the nucleus of cells. The code in the DNA "tells" the body which proteins to make. RNA has several vital roles in the body, including reading the DNA's instructions for making proteins, transporting these instructions out of the nucleus to the site of protein synthesis in the cell and then enabling the cell to make the proteins.
The origin of life is a fascinating topic to consider. The idea that chemicals were brought to the early Earth via meteorites is often suggested. It's interesting that a simple chemical such as formic acid is important in our lives today and may have been even more important in the distant past.
References and Further Reading
- Yellow crazy ants and formic acid from the Queensland Government
- Formic acid produced by tawny crazy ants from the American Chemical Society
- Conflict between tawny crazy ants and fire ants from Science Direct
- Formic acid in the common stinging nettle from Cambridge University
- Methanol and formic acid toxicity from Medscape
- Aspartame safety from Health Canada (a government agency)
© 2011 Linda Crampton
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