The Best of Pill Pushing- Why dogs eat grass and monkeys eat dirt - (3/1/2021)

By Dr. Ron Gasbarro

When humans feel ill, they go to the doctor to get a diagnosis and a prescription. And often, humans can diagnose their own infirmities and go to the pharmacy and select a remedy right off the shelf. Tummy ache? Pepto-Bismol. Headache? Execedrin. Finger cut? Neosporin and a Band-Aid. 

What do wild animals do when they are not feeling well? They do not have a pharmacy to purchase these items. But they do have remedies to help them feel better. This practice is called zoopharmacognosy. Zoopharmacognosy is a behavior in which non-human animals self-medicate by selecting and ingesting or topically applying plants, soils, and insects to prevent or reduce the harmful effects of pathogens and toxins. The term is derived from the Greek, meaning zoo ("animal"), pharma ("drug"), and gnosy ("knowing").

Antifungals in the jungle 
Scientific evidence indicates that animals have knowledge of natural medicines. In fact, they have access to the world's largest pharmacy: nature itself. Zoologists and botanists are beginning to understand how wild animals use plant medicines to prevent and cure infestations such as funguses and worms.

Wild animals generally will not hunt for a remedy unless they need it. Scientists studying baboons at the Awash Falls in Ethiopia noted that although the tree Balanites aegyptiaca (Desert date) grew all around the falls, only the baboons living below the falls ate the tree’s fruit [Admassu, 2013]. These baboons were exposed to a parasitic worm found in water-snails. This particular type of date is known to repel the snails. Baboons living above the falls were not in contact with the water-snails and therefore had no need of the medicinal fruit.

Many animals eat minerals like clay or charcoal for their curative properties. Colobus monkeys on the island of Zanzibar have been observed stealing and eating charcoal from human bonfires [Struhsaker, 1997]. The charcoal counteracts phenols – a corrosive poisonous acidic compound – produced by the mango and almond leaves which make up their diet.

Birds do it, bears do it, even educated deer do it
Some species of South American parrot and macaw are known to eat clay with a high kaolin content [Munn, 1994]. The parrots’ diet contains toxins because of the fruit seeds they eat, such as apple seeds which contain toxic cyanide. The kaolin clay absorbs the toxins and carries them out of the birds' digestive systems, leaving the parrots unharmed by the poisons. Kaolin has been used for centuries in many cultures as a remedy for human gastrointestinal upset (e.g., the original Kaopectate formulation).

A wide range of animals self-prescribe the substances around them when they need a remedy [Shurkin, 2014].
• Bears, deer, elk, and various carnivores, as well as great apes, are known to consume medicinal plants apparently to self-medicate.
• Some lizards are believed to respond to a bite by a venomous snake by eating a certain root to counter the venom.
• Baboons in Ethiopia eat the leaves of a plant to combat the flatworms that cause schistosomiasis.
• Fruit flies lay eggs in plants containing high ethanol levels when they detect parasitoid wasps, a way of protecting their offspring.
• Red and green macaws, along with many animals, eat clay to aid digestion and kill bacteria.
• Female woolly spider monkeys in Brazil add plants to their diet to increase or decrease their fertility.
• Pregnant lemurs in Madagascar nibble on tamarind and fig leaves and bark to aid in milk production, to kill parasites, and to increase the chances of a successful birth.
• Pregnant elephants in Kenya eat the leaves and even the trunks of the Geiger tree to induce delivery.

The types of self-medication
All animals – including humans – self-medicate and do so for 2 reasons [Lozano, 1998]
• Prophylactic self-medication –  Used in the prevention of illness by healthy animals
         + You take calcium supplements to keep your bones strong 
• Therapeutic self-medication – A specific response to a particular situation, that is, the deliberate consumption of medicinal substance by an ill animal  
+ You take an aspirin because you have a headache 

The types of zoopharmacognosy
The kinds of self-medication that wild animals use are related as to where they obtained the medicine:
• Dirt – Also known as geophagia (i.e., eating dirt)
• Insects – Also known as anting 
• Plants taken internally - Leaves, bark, trunks 
• Plants used externally – Also known as fur-rubbing

Dirt as medicine
Both bats and primates (monkeys, apes, etc.) practice geophagia. Chimpanzees in Uganda, have been observed consuming soil rich in kaolinite clay shortly before or after eating plants including the leaves of the flowering Trichilia rubescens, which possesses antimalarial properties in the laboratory [Krief, 2004]. Ostensibly, the chimps have made the connection between mosquitoes and malaria and use the clay to settle their stomachs after ingesting the protective plant. 

In the Great Lakes region, scientists have observed double-crested cormorants eating small stones [Robinson, 2009]. Birds commonly eat stones to aid digestion, but these stone-eating birds were plagued by nematode parasites (e.g., roundworms). To eliminate the worms, those birds in areas with higher parasite infestation tended to eat small stones more often.

Some species of bats regularly visit mineral or salt licks [Voigt, 2008]. However, this is not to increase their mineral consumption because both mineral-deficient and healthy bats visit salt licks at the same rate. Rather, researchers have observed that the presence of bats at salt licks increases during periods of high energy demand. The conclusion is that the primary purpose for bat visits to salt licks is for detoxification purposes, compensating for the increased consumption of toxic fruit and seeds. This was shown to be especially evident in lactating and pregnant bats, as their food intake increases to meet higher energy needs. 

Insects as medicine
Anting is a self-anointing behavior during which birds rub insects, usually ants, on their feathers and skin. The bird may pick up the insects in their bill and rub them on the body (active anting). Or the bird may lie on a highly populated insect colony – such as an anthill – and perform dust bathing-like movements (passive anting). The insects secrete liquids containing chemicals such as formic acid, which can act as an insecticide, miticide, fungicide, or bactericide [Osborn, 1998]. Alternatively, anting could make the insects edible by removing the distasteful acid, or, possibly by supplementing the bird's own preen oil. Instead of ants, birds can also use millipedes. Researchers hypothesize that benzoquinones secreted by millipedes repel mosquitoes and that ant-derived formic acid also helps keep feathers free of irritating insects. Opinion is still mixed as to whether birds are bathing in ants’ acid for food, cleanliness, fun, or some combination thereof. The same reasons one might go to a high-scale spa. Only birds get the same treatment for free! Birds have also been observed performing anting behavior with things other than ants, including beetles, lemon rinds, and even lit cigarette butts. 

Plants as internal medicine
Scientists recently discovered, for example, why monarch butterflies are so picky when it comes to choosing the milkweed plants on which to lay their eggs [de Roode, 2008]. The females often taste a plant, reject it, and fly away. It turns out that this finickiness is a form of self-medication. Butterflies infected with the protozoan parasite Ophryocystis elektroscirrha seek out milkweeds containing high levels of cardenolide, a plant steroid that interferes with parasite growth in monarch caterpillars.

Most scientific studies of animal self-medication focus on the great apes. Anthropologists have observed chimpanzees in Tanzania eating aspella leaves, which have no nutritional value [Shurkin, 2014]. The chimps were swallowing the leaves whole. Other scientists noted the same in other chimp colonies. Without chewing, the animals were not getting much nutritional benefit. So why do it?

The suggestion from biologists was that the chimps were self-medicating. One primatologist saw a parasite-ridden, constipated chimpanzee in Tanzania chew on the leaves of a noxious plant it would normally avoid. By the next day, the chimpanzee was completely recovered [Huffman, 1997]. The plants had bristly leaves, rough to the touch. The primatologist theorized that the chimps were swallowing the plants to take advantage of that roughness, using the leaves and stems to scour their intestines and rid themselves of parasites. Other researchers observed the same practice among other apes across Africa.

Researchers have established widely used criteria for judging when an animal is self-medicating: 
• First, the plant eaten cannot be a regular part of the animal’s diet; it is used as medicine, not food.
• Second, the plant must provide little or no nutritional value to the animal. 
• Third, the plant must be consumed during those times of year—for example, the rainy season—when parasites are most likely to cause infections. 
• Fourth, other animals in the group do not participate [Fruth, 2014]. 
If the activity meets these standards, it is safe to assume the animal is self-medicating.

And of course, who has not seen a dog chomping down on grass only to vomit up her stomach contents? While the majority of people believe that the dog is treating a gastrointestinal upset, others dispute this idea. A WebMD report suggests that most dogs that eat grass are not unwell beforehand. In fact, fewer than 10% of dogs seem to be sick before eating grass, according to their owners. And grass-eating does not usually lead to throwing up – less than 25% of dogs that eat grass vomit regularly after grazing.

Other suggested reasons why a dog might be eating grass include improving digestion, treating intestinal worms, or fulfilling some unmet nutritional need, including the need for fiber. One published study reports on a miniature poodle that ate grass and then vomited every day for 7 years [Kang, 2007]. Three days after putting the dog on a high-fiber diet, the owner reported that the dog stopped eating grass entirely. And, of course, there is also the possibility that your dog simply likes the way grass tastes or feels.

Plants as external medicine
Fur-rubbing is a behavior performed by all capuchin monkey species [DeJoseph, 2002]. Fur-rubbing is seen in both free-ranging and captive capuchins. The substances that elicit this behavior are pungent and/or stimulating when applied to the body. The monkeys rub with plants such as citrus fruit, onions, tobacco, Clematis dioica and Piper marginatum – sort of like the human version of Hai Karate or Aqua Velva. Piper marginatum, a medicinal plant, is used by humans to relieve pain, swelling, and fever; it is insect repellent, antibiotic and antifungal.  Although there are hundreds of Piper species in the Americas, the monkeys and humans focus their use on those with a licorice scent, an indication of bioactivity, that is, potency as a pharmaceutical agent. Fur-rubbing behavior occurs primarily during the wet season. The function of this behavior may be for wound and ectoparasite treatment. It may reinforce social bonds or the monkeys may simply enjoy rubbing. Par-tay!

Orangutans exhibit fur-rubbing for medicinal use. They have been observed using a species of Commelina (dayflower), a prized herb in the peat-swamp forests of Central Kalimantan, Borneo, as either an antibacterial or anti-inflammatory agent. In Central Kalimantan, local indigenous people use the same species as an external medication to treat their arms after a stroke, for muscular pain, and for sore bones and swellings. Thus, the possible convergence of human and orangutan use of Commelina may indicate that orangutans are using it for a similar purpose.

Should we go back to the wild?
While animals in the wild instinctively know how to heal themselves, humans have all but forgotten this knowledge because of our misplaced connection with nature. Since wild animals have been observed actively taking care of their own wellbeing, it raises questions of how we approach healthcare with natural remedies, not just for ourselves but for our pets and farm animals too.

Ron Gasbarro, PharmD, is a registered pharmacist, medical writer, and principal at Rx-Press.com. Read more at www.rx-press.com

This article is for informational purposes only. Reliance on any information appearing in this article is solely at your own risk.

References
Admassu M, Bekele A, Kim J.  Nutritional composition of Balanites aegyptiaca (desert date) and Hyphaene thebaica (doum palm) fruits consumed by Hamadryas baboons (Papio hamadryas hamadryas) in Awash National Park, Ethiopia. J Nutr Ecol Food Res. 2013;1:198–206.
 
de Roode JC, Pedersen AB, Hunter MD, Altizer S. Host plant species affects virulence in monarch butterfly parasites. J Anim Ecol. 2008;77:120-6. 

DeJoseph M, Taylor RS, Baker M, Aregullin M. Fur-rubbing behavior of capuchin monkeys. J Am Acad Dermatol. 2002;46:924-5.

Fruth B, Ikombe NB, Matshimba GK, et al. New evidence for self-medication in bonobos: Manniophyton fulvum leaf- and stemstrip-swallowing from LuiKotale, Salonga National Park, DR Congo. Am J Primatol. 2014;76:146–58.

Huffman M. Current evidence for self-medication in primates: A multidisciplinary perspective. Yearb Phys Anthropol. 1997;104(suppl 25):171–200.

Kang BT, Jung DI, Yoo JH, Park C, Woo EJ, Park HM. A high fiber diet responsive case in a poodle dog with long-term plant eating behavior. J Vet Med Sci. 2007;69:779-82.

Krief S, Martin MT, Grellier P, Kasenene J, Sévenet T. Novel antimalarial compounds isolated in a survey of self-medicative behavior of wild chimpanzees in Uganda. Antimicrob Agents Chemother. 2004;48:3196-9.

Lozano GA. Parasitic stress and self-medication in wild animals. In: Møller AP, Milinski M, Slater PJB (eds.); Advances in the Study of Behavior; Volume 27; New York: Elsevier, Inc.; 1998. 

Morrogh-Bernard HC. Fur-Rubbing as a form of self-medication in Pongo pygmaeus. Int J Primatol. 2008; 29:1059–64. 

Munn CA. Macaws: winged rainbows. National Geographic. 1994;185:118–40.

Osborn SAH. Anting by an American Dipper (Cinclus mexicanis). The Wilson Bulletin. 1998;110:423-5.

Robinson S, Forbes M, Hebert C. Is the ingestion of small stones by double-crested cormorants a self-medication behavior? The Condor. 2009;110: 782-5. 

Shurkin J. Animals that self-medicate. Proc Natl Acad Sci U S A. 2014;111:17339-41.

Struhsaker TT, Cooney DO, Siex KS. Charcoal consumption by Zanzibar red Colobus monkeys: Its function and its ecological and demographic consequences. Internat J Primatol. 1997;18:61-72.

Voigt CC, Capps KA, Dechmann DK, Michener RH, Kunz TH. Nutrition or detoxification: why bats visit mineral licks of the Amazonian rainforest. PLoS One. 2008;3:e2011.

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