You’ve likely encountered the viral meme: a charming image of a Virginia opossum paired with text emphasizing their tick-eating prowess, urging appreciation for these creatures due to their supposed tick consumption. While variations of this meme abound, often inflating the number of ticks consumed to thousands per week or season, the core message remains consistent: if ticks are your nemesis, opossums should be your allies. However, this widely circulated sentiment harbors a significant flaw: it’s simply not true.
The Student’s Inquiry and the Quest for Truth
This popular meme came under scrutiny during a wildlife course at Eureka College when a student, Kaitlyn Hild, questioned its validity. Drawing upon my experience with opossums, I expressed skepticism and encouraged Hild to investigate the claim’s origins. Her research led us to a scientific paper titled, Hosts as ecological traps for vectors of Lyme disease. Upon reviewing the paper, we found ourselves with more questions than answers, prompting a deeper investigation.
We embarked on a research project, obtaining a scientific collection permit from the Illinois Department of Natural Resources to analyze the stomach contents of road-killed opossums. After several seasons and only collecting eleven specimens, we sought a more reliable source. A local nuisance wildlife trapper provided us with a freezer full of carcasses, ethically euthanized. Each opossum was examined for ticks before dissection and stomach removal. Then, the meticulous task began: Hild meticulously analyzed the contents of 33 opossum stomachs under a dissecting microscope, categorizing each food item.
Simultaneously, I delved into existing scientific literature on opossum diets, uncovering 23 published accounts, including early research from 1851 by John James Audubon. Later, more comprehensive studies, such as Bill Hamilton’s paper analyzing the diet of 186 opossums, mirrored our methodology. Collectively, these publications detailed the dietary analysis of over 1,280 opossums across their US range. Remarkably, none of these studies, including our own, reported finding ticks in the stomachs or any part of the digestive tracts of Virginia opossums.
Hild’s findings from the stomach content analysis were equally surprising – or rather, unsurprising in their lack of ticks. She identified worms, a discarded French fry, fragments of glass, and even a largely undigested shrew, but no ticks. She did find three intact fleas, potentially indicating grooming behavior, but still no ticks. Even with initial expectations of finding at least some ticks, the complete absence was notable.
Our research culminated in a published paper in the International Journal of Ticks and Tick-Based Diseases, confirming the clear results: no ticks were found in opossum stomachs in our study, and there was no prior evidence of ticks in the diets of Virginia opossums within the scientific literature. This begged the question: where did this pervasive “fact” about opossums as tick-eating machines originate?
The Genesis of the Tick-Eating Myth
The paper that sparked our investigation was authored by researchers in New York state studying the role of various vertebrate species in harboring blacklegged ticks (Ixodes scapularis), vectors of Lyme disease. They live-captured four opossums and housed them in a lab, introducing 100 larval blacklegged ticks to each. Similar experiments were conducted on chipmunks, squirrels, mice, veeries, and catbirds. The animals were observed for four days, after which researchers counted the ticks that had fed and detached.
Unlike the kennels of other species, the opossum enclosures had very few detached ticks. The researchers, without combing the opossums or examining stomach contents, concluded that the missing ticks must have been consumed by the opossums. Thus, the myth of the tick-devouring opossum was born.
Physiological Insights Debunking the Myth
This conclusion overlooked key physiological characteristics of opossums. Opossums possess a lower metabolism compared to the other tested species, resulting in a lower body temperature and blood pressure. Research indicates that ticks feed more slowly in cooler temperatures and on hosts with lower blood pressure. After four days, it’s highly probable that the ticks were still attached to the opossums, slowly feeding. A simple combing of the opossums before release could have confirmed this, but it wasn’t done. Stomach content analysis, or even scat examination for indigestible tick parts, was also omitted.
The exaggerated numbers in the tick-eating memes stemmed from a creative, yet flawed, extrapolation of the experimental data. On average, only 3.5 ticks detached from the four opossums during the lab observation, a mere 3% of the ticks introduced. Other studies in New York State have found opossums carrying an average of 199 (±90) larval ticks during tick season. The researchers then reasoned backward, suggesting opossums must host over 5,500 larval ticks, theorizing that 97% are groomed off and eaten, leaving only 199 to be counted on wild animals. This led to the claim that opossums eat 5,301 ticks (97%) each tick season. However, there’s no evidence supporting opossums hosting such high tick loads or consuming any significant number of ticks. This mathematical leap of faith gave rise to a misleading narrative.
The fact that these claims passed peer review highlights the importance of critical thinking in science. Even peer-reviewed publications can contain flawed conclusions, especially when extraordinary claims are made.
The Intrinsic Value of Opossums Beyond Tick Control
Ultimately, does the tick-eating myth truly matter? Perhaps it encourages some to view opossums more favorably, preventing harm to these often-misunderstood creatures. After all, opossums could certainly benefit from positive public relations. However, the danger lies in people actively attracting opossums to their properties, believing they will control tick populations while scavenging for scraps. Attracting opossums with food inevitably attracts other wildlife, including raccoons, feral cats, rats, foxes, and coyotes.
This practice creates two significant problems. First, it leads to wildlife associating humans with food, a common precursor to aggressive behavior towards humans, often resulting in the removal (death) of these animals. Many documented coyote attacks, for instance, occur in suburban areas where residents intentionally feed coyotes, conditioning them to associate humans with food sources. Second, concentrating wildlife around food sources increases the risk of disease transmission amongst animals and to humans. Ironically, research into opossums as a means to reduce Lyme disease risk may inadvertently increase human exposure to other wildlife-borne diseases due to intentional feeding.
Opossums are valuable members of our ecosystems for reasons beyond pest control. They are scavengers, playing a crucial role in cleaning up carrion and preventing disease spread. They are also seed dispersers, contributing to forest regeneration. Furthermore, they serve as prey for larger predators, supporting food webs.
Opossums are North America’s only native marsupial north of Mexico, with Mexico hosting nine species. Their prehensile tails, while not designed for hanging from branches for extended periods (contrary to popular images), are used to carry nesting materials. Opossums are remarkable creatures in their own right. They don’t need to be mythical tick superheroes to deserve our respect and appreciation. Their ecological roles and unique adaptations make them a fascinating and important part of our natural world.
