The rhinoceros stomach botfly is a hard bug to love.
In its larval stages, the fly uses mouth hooks and spines to attach itself to the stomach linings of black or white rhinos, appearing some time later in the mammals' dung, from which it quickly buries itself in the ground.
Six weeks later, an adult fly emerges – the largest known fly species in Africa. Adult rhino botflies are more than 11/2 inches in length, have 3-inch wingspans and look like giant wasps with orange-red heads and legs.
South African National Parks
The gastrointestinal tract of southern white rhinos provides a safe and singular home for the developing larvae of the rhinoceros stomach botfly. If the rhino goes extinct (it's endangered), so, too, will the botfly.
Despite their appearance, the flies are harmless – to rhinos and humans. Adult flies have rudimentary mouthparts and probably don't eat at all. They live only three to five days, just long enough to mate and lay eggs upon the heads of unsuspecting rhinos. The great beasts don't seem to mind. Healthy rhinos have been known to carry great gutfuls of the larvae with no ill effect.
Indeed, rhinos face much bigger problems than the botfly. Habitat loss and overhunting have pushed all five rhinoceros species in the world toward extinction. In some cases, over the brink. In July, the World Conservation Union declared a West African subspecies of the black rhinoceros to be tentatively extinct. No living specimens have been sighted for several years. Other subspecies are hanging on with varying degrees of success.
If the rhinos go, so, too, will the rhinoceros stomach botfly.
To be sure, no one's crying out to save the rhino maggot. Nor, for that matter, is there much clamor about conserving any other imperiled parasite, from lice and mites to worms, bacteria and other microorganisms. They aren't majestic like rhinos or warm and fuzzy like pandas. Rather, they're usually small, often revolting to human sensibilities and occasionally harmful.
But if they disappear, their absence would be sorely felt. Or should be.
One down, two to go
In 2004, six biologists representing universities from Singapore to Connecticut to Scotland published a seminal paper on the state of co-dependent species around the world. They noted that the World Conservation Union listed more than 12,200 animal and plant species considered to be endangered. (The 2006 list ups the total to 16,118.)
The bird louse Colpocephalum californici lived only on California condors. When the last wild condors were captured in the 1980s for captive breeding, conservationists fumigated the birds for parasites, inadvertently wiping out the last of that lice species.
The “Red List” did not include, however, the researchers' estimated 6,300 “affiliate species” that depend upon endangered species for their livelihood and survival. The list includes not just parasitical organisms like the rhino botfly, but also species in mutualistic relationships, such as pollinators of specific plants.
The scientists' central point: For every free-standing species that becomes extinct, perhaps one or more other species also die out.
Until relatively recently, nobody much cared. In 1987, for example, biologists captured the last remaining wild California condors – 22 birds – for a captive breeding program intended to preserve the endangered species.
As part of that process, the birds were fumigated with carbaryl powder to rid them of perceived pests, such as lice and mites.
The birds weathered the fumigation just fine. Indeed, there are now 289 California condors, 138 of them released into remote areas of California, Arizona and Mexico.
But another species went extinct. Colpocephalum californici was an avian chewing louse that looked pretty much like all other lice. It boasted just one distinction: It lived only on California condors. When conservationists at the San Diego and Los Angeles zoos fumigated the last wild condors, they most likely wiped out the last C. californici.
“There wasn't a lot of awareness back then about these lice or parasites in general,” said Oliver Ryder, a senior scientist and geneticist for the San Diego Zoo's Center for the Reproduction of Endangered Species (CRES). “Plus, in many cases, it's the law to eradicate parasites. The U.S. Department of Agriculture, for example, required us to destroy all of the ticks on some rhinos we imported from the wild some years back. The rules didn't – and don't – allow us to save some organisms for biodiversity's sake. There are concerns that some parasites could pose a disease threat to native or agricultural species.”
As far as scientists can tell, based on very limited knowledge, C. californici caused its condor hosts no harm. The bird was simply a mobile home, providing shelter and the occasional feather meal.
Roger Payne, Whale Conservation Institute; Vicki Roundtree, University of Utah
Individual right whales can often be identified by the "whale lice" they carry. The lice, which are actually harmless crustaceans hitching a ride,congregate in whitish clumps on the whales' skin, forming unique patterns.
“Killing off the last C. californici was a mistake,” said Heather Proctor, an associate professor of biological sciences at the University of Alberta in Edmonton, Canada, and one of the authors of the 2004 parasite paper. “I can understand why it happened, but it was unfortunate.”
But the loss is larger than the louse; lost, too, was knowledge.
In a paper published last year in the journal Animal Conservation, Noah Whiteman, a postdoctoral student at the University of Missouri, observed that parasites can tell scientists quite a bit about their hosts.
But maybe more importantly, they are great repositories of history, living chronicles of how organisms evolve over time. When University of Utah biologists sought to study the history of endangered right whales, they turned to its “whale lice” – small, harmless crustaceans that hitchhike aboard whales for their entire lives, eating sloughed skin, sharing a common ecological and evolutionary history with their leviathan hosts.
Because the lice reproduce so much faster than whales and because they are so abundant (a single whale might have 10,000 resident crabs grouped in white, callus-like patches on the skin), whale lice genes can actually reveal more about whales than the marine mammals' own genome.
In this case, researchers were able to show that right whales split into three separate species 5 million to 6 million years ago, each occupying a different ocean.
Parasite studies have been used to reveal the demographics of Rocky Mountain cougars (by tracking feline immunodeficiency virus) and human migration patterns (via stomach bacteria). The genetics of human head lice indicate modern humans once came in contact with an unknown hominid species.
Cassowaries are large, flightless birds found in New Guinea and Australia. Habitat loss threatens the birds' existence and, by extension, a symbiotic feathered mite called Hexacaudalges found only on cassowaries.
Some parasites, of course, are harmful. Mosquitoes are notorious vectors for malaria, which kill 1 million people a year. There is a species of human botfly whose larvae create gruesome, boil-like cysts on the skin. But true parasites do not kill their hosts. It's not in their best interest. And some, notes Proctor, are actually beneficial and necessary.
Certain bacteria in the gut, for example, are vital to a healthy gastrointestinal tract. A parasitic worm has been shown to help prevent asthma, probably by modifying the body's immune response.
“Anything that has the moniker of parasite used to be considered an endangerment to a species,” said Proctor. “But interesting things are coming out of human medical science. People are starting to realize that a really clean (and parasite-free) host may not necessarily be a healthy one.”
Officials at CRES are collaborating with Diversa, a San Diego-based biotech company to study microorganisms in captive animal species. Diversa is bioprospecting. That is, it's looking for organisms with properties that might be exploited for new pharmaceuticals or medical treatments. CRES seeks to better understand the dynamic relationships between captive animals and their co-dependents.
“Keeping some animals healthy is a real challenge,” said Ryder. “There are dietary specialists like the koala (which eats only eucalyptus leaves) and the panda (which eats only bamboo). Those are success stories, but there are other species where we really don't know what they eat in the wild. They live in the inaccessible top canopy of the forest. Or they're very shy. By examining and comparing gastric microflora, we might learn something new.”
Right to life
From a certain philosophical point of view, it can be argued that all organisms, from viruses to blue whales, have an intrinsic right to live. That may be so, but in a world dominated by humans and their activities, the hard reality is that some species cannot and will not survive.
Estimates of the number of animals and plants that go extinct each year vary hugely, up to 140,000 species annually. Whatever the actual number, most of these organisms (typically insects) disappear without ever having been discovered and named. Their life secrets die with them.
Even if people wanted to, conservationists concede there aren't sufficient resources to save every threatened species. Choices must be made, priorities established.
“We all have a set of reasons for why we value species. These include ecological value, intrinsic value, aesthetic value and economic value,” said Rob Dunn, an assistant professor of zoology at North Carolina State University and an author of the 2004 parasite study.
“It is useful to compare how a rare parasite and a rare rhino stack up on these values. The rare parasite and rare rhino would have similar ecological, intrinsic and economic values. If anything, the parasite would have a higher likelihood of having high economic value because of the potential medicinal value of many parasites. The rhino, by dint of its rarity, has little remaining ecological value – and only to a small area.
“The only way that rhinos and parasites stack up differently is in terms of aesthetic values. If we conserve only rhinos and other big things, the decision we are essentially making is that we will conserve only those things that we find pleasing. Do we really want to be a society that decides the fate of species based solely on beauty? For my part, I find many of the parasites lovely, fascinating, bizarre and worthy of years of study.”
But Dunn said it's rarely necessary to actually choose between species. “Many of the conservation strategies we use to conserve vertebrates will also conserve their parasites and mutualists. Conserving lots of habitat will often work for both groups.”
Save the big, in other words, and you save the small. But whether humanity will do so remains unclear.
“Depending on what happens to human societies, we will spend the next few generations coming to terms with what we have lost,” said Dunn. “We won't know most of what we have lost because it will have never been named. Some of the species we will have lost will have had important medicinal values. Some of them will have pollinated our crops. Some of them will have been strange creatures deserving explanation. Some will have been beautiful. Some will have had values that we are not yet capable of understanding.
“We live in a vast living museum that is being flooded and burned and ravaged. We know that we must save some of the art, but we don't know anything about the art. So we grab the showiest things and hope they are important.”
Like the rhino and the botfly.