No question, ticks are a scourge, and this year seems to be exceptionally bad. Naturally, any creature with a healthy appetite for these annoying arachnids will be more welcome around home and garden, not to mention the local woodlot. While they may not be the most attractive critters in the neighborhood - looking very much like an over-sized rat - Virginia opossums (Didelphis virginianus) or as they’re more commonly known, possums do have a reputation as ravaging tick consumers. But is that reputation well deserved? One recent study suggests their value as pest eradicators maybe overblown.
Part of the perception of possums as tick destroyers may have come from a study published in 2009 by the Royal Society. Researchers tested several species, including possums by subjecting them (in captivity) to larval blacklegged ticks (a.k.a. deer ticks). They found that possums killed 83-96% of the ticks that attempted to attach and feed, a much higher rate than the other five test species. Ecologists at the Cary Institute for Ecosystem Studies in Millbrook, N.Y. then extrapolated these findings to estimate that in one season, a possum can kill about 5,000 ticks.
However, a 2021 study published in Ticks and Tick-borne Diseases came up with a different conclusion. They examined stomach contents from 32 possums collected in the wild in central Illinois under a dissecting scope to look for ticks or tick body parts and found no evidence. They also questioned the methods of the previous study, noting that the researchers did not examine the study animals for ticks still attached after 4 days, but merely assumed if they did not fall off, they had been eaten. And, they performed a vigorous literature search for corroborating evidence of tick ingestion including 23 manuscripts that describe diet analyses. None identified ticks as a diet item. The Illinois researchers concluded that ticks are not a preferred diet item for possums.
So where does that leave us? Researchers in the first study exposed possums to 100 ticks for 4 days, counted the ticks that fell off, assumed the rest were eaten (possums are fastidious groomers) and came up with a consumption rate over 90%. Those in the second study, and the literature they reviewed found no evidence whatsoever that possums consume ticks. But does that mean they avoid them?
Ecologically, possums are classified as omnivores, with invertebrates making up between roughly 60% to 70% of their diet. It seems unlikely they would avoid an easily available food source, especially one they can find crawling around on their own bodies. However, the Illinois study seems to suggest they might, though they couched their conclusion slightly by saying ticks are “not a preferred diet item.” Perhaps they don’t seek them out, but still eat them when they can.
Those researchers also noted, “Considering that wildlife unconditioned to laboratory conditions may exhibit non-typical behaviors, we recommend that lab-based studies of wildlife behavior be ground-truthed with studies based in natural conditions.” While not directly stated, implied within is that more research is needed before we can conclusively rule out possums as non tick eaters. In the meantime, we’re still left with staying home, treating our clothes with arachnicide or doing a meticulous tick check after each outing.