This photo available under a Creative Commons license shows a great bustard. These birds, especially the males, selectively eat blister beetles that contain toxic cantharidin, but because the toxin is lethal to the birds except at very low doses, only one or two at a time. This toxin is known, from in vitro experiments in the lab, to kill fungi, round worms, and bacteria. (Francesco Veronesi / Flickr)

This photo available under a Creative Commons license shows a great bustard. These birds, especially the males, selectively eat blister beetles that contain toxic cantharidin, but because the toxin is lethal to the birds except at very low doses, only one or two at a time. This toxin is known, from in vitro experiments in the lab, to kill fungi, round worms, and bacteria. (Francesco Veronesi / Flickr)

On the Trails: Self-medication by many animals

Examples come from many kinds of critters.

Humans have self-medicated for ages, in various ways (not always healthy ones!), commonly using plant-derived materials applied externally or used internally. Although many of these uses remain in the realm of myth and wishful-thinking, some have been scientifically shown to be effective, at least in certain circumstances, although the sample sizes are usually small and the studies need replication.

I take a walk every day and find that this almost always improves my outlook on life. Walking can serve many functions, often overlapping and interacting, including exercise, observations and exploration, socializing (and, if I am lucky, a friendly canine greeting), contemplation and assessment. I find it useful in all those ways and typically feel better after a walk, so, in effect, this is a form of self-medication — one that is unlikely to be harmful.

Other animals may self-medicate too, although the evidence is largely suggestive and needs fundamental experimental documentation. The circumstantial evidence lies in observations that strongly, logically, indicate a medical function but, of itself, it is not proof. Examples come from many kinds of critters.

— European wood ants incorporate lots of solidified conifer resin in their nests. This reduces the growth of micro-organisms (as it does in the originating trees).

— Certain tiger moth caterpillars (sometimes called woolly bears, but not the same as the ones we call by that name) selectively eat particular kinds of plants containing alkaloids that increase survival of individuals parasitized by tachinid flies.

— Fruit flies, which can be parasitized by certain wasps, seek out foods that provide ethanol. Ingestion of this alcohol decreases oviposition by the wasps and increases the death of any wasp larvae already in the host fly. (Note: this only works with generalist wasp species, not with the species that specializes on fruit flies).

— Monarch butterfly caterpillars feed on milkweed plants but don’t favor any particular species. Mama does it for them: if she is infected by parasites, she oviposits preferentially on milkweeds that reduce parasite growth in the caterpillars.

— Chimpanzees and other great apes in Africa sometimes eat parts of plants that have little nutritional value (e.g., bark) as well as whole leaves and clay. These dietary choices may be useful against intestinal parasites.

— Starlings (and many other birds) often place bits of aromatic herbs (such as fleabane and wild carrot) into their nests during the nest-building process. Males begin the nest building in a cavity, later joined by a female; experienced, adult males are more selective of particular plants than are first-year males. Placement of the herbs continues until the eggs hatch. The volatile compounds in the aromatic herbs in one experiment reduced infestations of blood-sucking mites on nestlings, although nestling survival did not improve significantly. Another experiment found no difference in the numbers of mites on the nestlings, and no difference in nestling survival, but a significant difference in chick survival to age one year.

— Hummingbirds in Patagonia select a rare moss for nest material, constructing most of the nest with this moss. The preferred moss has effective antimicrobial activity, and it also has toxic compounds that might deter predation on eggs and chicks by small mammals.

— Some parrots in some parts of Amazonia gather at clay banks, eating the clay. Some researchers suggest that the clay may neutralize toxins in the seeds that parrots eat, but others claim that the birds are getting scarce minerals, such as sodium. Still another notion is that adult parrots feed the clay to their chicks, which do not have much resistance to toxins.

— Songbirds sometimes hold ants (or millipedes) in their bills and smear the ants over their feathers; or sometimes they just sit closely on ant nests and let the ants crawl over them. Anting may deposit some formic acid on the birds’ skins, which could deter ectoparasites or just feel good or something else.

— Great bustards are big ground-dwelling birds of Eurasia. Males gather on communal display grounds called leks in the mating season, displaying vigorously and trying to attract females. The energetic displays divert energy from the immune system, so it is less effective. These birds, especially the males, selectively eat blister beetles that contain toxic cantharidin, but because the toxin is lethal to the birds except at very low doses, only one or two at a time. This toxin is known, from in vitro experiments in the lab, to kill fungi, round worms, and bacteria (although its activity in bustards has not been tested directly). Males (more than females) also prefer to eat certain plants (a poppy and a bugloss) containing compounds that are effective against protozoan and round-worm parasites. Selective eating of beetles and these plants has only been documented for the Spanish population of bustards, which is geographically isolated from other populations.

The courtship display of male great bustards includes raising and exposing the rear end, where the digestive and genital tracts end in a common cavity (the cloaca). A courting male presents his rear end to a prospecting female, which inspects the cloaca very closely. The cloacal opening is surrounded by small white feathers, where parasites or traces of diarrhea would be visible to a female. Absence of parasites (and resistance to the toxin) would be good indicators of male health, which in combination with other traits, allows the female to make a good choice. Females are extremely choosy and most males don’t get a mate.

A lot remains to be learned about self-medication!

• Mary F. Willson is a retired professor of ecology. “On the Trails” appears every Wednesday in the Juneau Empire.

A hummingbird of Patagonia sits on her nest made of special mosses. (Courtesy Photo / Estacion Biologica Senda Darwin)

A hummingbird of Patagonia sits on her nest made of special mosses. (Courtesy Photo / Estacion Biologica Senda Darwin)

More in News

(Juneau Empire file photo)
Aurora forecast through the week of Dec. 22

These forecasts are courtesy of the University of Alaska Fairbanks’ Geophysical Institute… Continue reading

Maria Laura Guollo Martins, 22, an Eaglecrest Ski Area employee from Urussanga, Brazil, working via a J-1 student visa, helps Juneau kids make holiday decorations during the resort’s annual Christmas Eve Torchlight Parade gathering on Tuesday. (Mark Sabbatini / Juneau Empire)
Foreign students working at Eaglecrest trade Christmas Eve traditions for neon lights and lasagna

26 employees from Central and South America are far from family, yet among many at Torchlight Parade.

An aerial view of L’áan Yík (Channel inside or Port Camden) with cars and people gathered on the bridge over Yéil Héeni (Raven’s Creek) during a May 2024 convening on Kuiu Island. Partners that comprise the Ḵéex̱’ Ḵwáan Community Forest Partnership and staff from the Tongass National Forest met to discuss priorities for land use, stream restoration, and existing infrastructure on the north Kuiu road system. (Photo by Lee House)
Woven Peoples and Place: U.S. Forest Service’s Tongass collaboration a ‘promise to the future’

Multitude of partners reflect on year of land management and rural economic development efforts.

The city of Hoonah is seeking to incorporate as a borough with a large tract of surrounding area that includes most of Glacier Bay National Park and a few tiny communities. (Alaska Department of Commerce, Community, and Economic Development photo)
New Xunaa Borough gets OK in published decision, but opponents not yet done with challenges

State boundary commission reaffirms 3-2 vote; excluded communities likely to ask for reconsideration.

Bartlett Regional Hospital leaders listen to comments from residents during a forum June 13 about proposed cuts to some services, after officials said the reductions were necessary to keep the hospital from going bankrupt within a few years. (Mark Sabbatini / Juneau Empire)
Bartlett rebounds from years of losses with profits past six months; staffing down 12% during past year

Hospital’s balance sheet shows dramatic bottom-line turnaround starting in May as services cut.

A street in a Mendenhall Valley neighborhood is closed following record flooding on Aug. 6 that damaged nearly 300 homes. (City and Borough of Juneau photo)
Flood district protection plan faces high barrier if enough property owners protest $6,300 payments

Eight of nine Assembly members need to OK plan if enough objections filed; at least two already have doubts.

Sunset hues color the sky and the snow at the University of Alaska Fairbanks campus on Feb. 26, 2024. The University of Alaska system and the union representing nearly 1,100 faculty members and postdoctoral fellows are headed into federal mediation in January. (Yereth Rosen/Alaska Beacon)
University of Alaska-faculty contract negotiations head for federal mediation

Parties say they’re hopeful; outcome will depend on funding being included in the next state budget.

The newly named Ka-PLOW is seen with other Alaska Department of Transportation and Public Facilities equipment in Juneau in a video announcing the names of three local snowplows in a contest featuring more than 400 entries. (Screenshot from Alaska Department of Transportation and Public Facilities video)
Newly named DOT snowplows probably won’t visit Juneau neighborhoods until after Christmas

Berminator, Salt-O-Saurus Rex, Ka-PLOW selected as winners in contest with more than 400 entries.

(Michael Penn / Juneau Empire file photo)
Police calls for Friday, Dec. 20, 2024

This report contains public information from law enforcement and public safety agencies.

Most Read