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How Opossums May Silently Help Prevent the Spread of Lyme Disease

August 01, 2017

Story at-a-glance

  • More than 96 percent of ticks that attempt to feed on opossums do not survive, as the animals consume them during grooming
  • Opossums act as “ecological traps” for larval ticks, hosting perhaps more than 5,500 in a season and consuming the majority of them before they reach maturity
  • Of the ticks that do successfully feed on opossums, very few of them pick up the bacteria that cause Lyme disease

By Dr. Becker

Maybe it’s their long, hairless tails and pointy noses, making them appear reminiscent of rats, that give opossums a bad reputation, but whatever the reason, these animals are deserving of far more accolades than they’re typically given. They’re actually one of my favorite animal species, and they’re the only marsupial found in the U.S. and Canada.

While many people are primarily interested in figuring out how to keep opossums out of their yards, there’s good reason to do just the opposite, as opossums present a formidable foe to ticks.

Research conducted by Rick Ostfeld, Ph.D., a senior scientist at the Cary Institute of Ecosystem Studies, and colleagues revealed that more than 96 percent of ticks that attempt to feed on opossums do not survive, as the animals consume them during grooming.1 Opossums act as “ecological traps” for larval ticks, hosting perhaps more than 5,500 in a season and consuming the majority of them before they reach maturity, he said.

Opossums ‘Hoover Up’ Ticks as They Wander the Forest

Opossums are often compared to vacuum cleaners, in part because of their indiscriminate diet. They’ll eat virtually anything they can find, from grass and nuts to garbage, insects, mice and snakes. However, the vacuum comparison has also been used to describe opossums’ voracious “appetite” for ticks. Ostfeld said in a Cary Institute of Ecosystem Studies news release:2

"[M]any ticks try to feed on opossums and few of them survive the experience. Opossums are extraordinarily good groomers it turns out — we never would have thought that ahead of time — but they kill the vast majority — more than 95 [percent] percent of the ticks that try to feed on them. So these opossums are walking around the forest floor, hoovering up ticks right and left, killing over 90 [percent] of these things, and so they are really protecting our health."

As for why opossums consume so many more ticks than other animals, Bard College professor of biology Felicia Keesing, Ph.D., suggested in an interview with VPR (Vermont’s NPR news source) that they may be more sensitive to the feeling of ticks on their bodies, allowing them to notice when they attach and easily pinpoint their locations for quick removal.3

I have had the honor of caring for two educational opossums (that were unable to be released in the wild), and they are the most sensitive creatures I have ever encountered. They can detect when they have foreign hairs stuck on them (like dog hair) as well as other tiny fibers (like cobwebs) that most creatures would not be sensitive enough to detect. I think this profound skin sensitivity contributes to their ability to detect ticks on their own bodies.

What else is interesting, Keesing noted, is that of the ticks that do successfully feed on opossums, very few of them pick up the bacteria that cause Lyme disease.

“Having ticks feed on opossums is really good for us because those ticks are really unlikely to become infected when they next take a meal, which could easily be on us or one of our pets … ,” Keesing said, “so opossums are helping us twice over because they’re killing a lot of ticks … and of those that do manage to feed on opossums, those come off as almost certainly harmless to us.”4

Opossums Are Resistant to Rabies and Snakebites — and Have Clever Forms of Self-Defense

In addition to helping curb the spread of Lyme disease, opossums are also resistant to rabies. This may come as a surprise to many, because opossums also drool excessively as a form of self-defense — a phenomenon many assume occurs because the animal is rabid.

In reality, they’re trying to fool predators into thinking they’re sick so they’ll leave them alone. And that’s not all. Opossums also “play ‘possum,’” as the saying goes, falling into an involuntary catatonic state to discourage predators (they basically faint from fear).

“They roll over, become stiff, close their eyes (or stare off into space) and bare their teeth as saliva foams around the mouth and a foul-smelling fluid is secreted from glands,” Mother Nature Network reported.5 “The catatonic state can last for up to four hours, and has proven effective as a deterrent to predators looking for a hot meal.”

Opossums are also immune to most snakebites, including that from rattlesnakes and cottonmouths, and researchers have isolated a protein in their blood that has potential as an anti-venom. Other toxins, like that from honeybee or scorpion stings, also leave opossums unscathed, making the creatures an intriguing source of study for scientists looking for the toxin-neutralizing factor in their blood.6 As mentioned, they are also more resistant to the rabies virus than other mammals.

‘Making Peace With the ‘Possum’’

Taken together, opossums are one of the gentlest and most beneficial animals in the forest, and even when they live in urban areas (which they adapt to quite well) add value to the ecosystem, posing little risk of harm to humans and pets. Opossums consume many “pests” besides ticks, including rodents, insects and carrion.

Their foraging helps to keep grounds clean and free of food that might attract other less desirable creatures, such that the Dallas/Fort Worth (DFW) Wildlife Coalition suggests they should be viewed as the great “groundskeeper.” If you see an opossum living in your backyard, please don’t attempt to kill it or relocate it (the latter of which may leave the animal with a less than 50 percent chance of survival, according to DFW Wildlife). Instead, they suggest “making peace with the ‘possum:’”7

When left alone, the opossum does not attack pets or other wildlife; he does not chew your telephone or electric wires, spread disease, dig up your flower bulbs or turn over your trash cans. On the contrary, the opossum does a great service in insect, venomous snake, and rodent control. He takes as his pay only what he eats, and maybe a dry place to sleep.

The ‘possum’ tolerates our pets, our cars, prodding sticks, rocks and brooms. ‘Attacks’ by opossums are simply non-existent. When he gets too close, or accidentally moves into your attic space, he can be easily convinced to move along. If you are lucky enough to have one of these guys come around, you can rest assured he is cleaning up what he can, and will soon move along to help someone else.”

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Sources and References

  • 1 Proc Biol Sci. 2009 Nov 22; 276(1675): 3911–3919.
  • 2 Cary Institute of Ecosystem Studies, Why You Should Brake for Opossums
  • 3, 4 VPR June 6, 2017
  • 5 Mother Nature Network November 14, 2012
  • 6 National Wildlife Federation March 30, 2015
  • 7 DFW Wildlife Coalition, Making Peace With the ‘Possum
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