Keep on Ticking: Entomologist Tells of Ticks’ 27-Year Lifespan
By Paige Embry
What does a person do with a bunch of ticks, given as a gift, that aren’t well-suited to their current research? If you’re Julian Shepherd, Ph.D., associate professor of biology at Binghamton University, you stick them in a habitat at a constant temperature and humidity and watch them—for the next 45 years.
Shepherd writes about what he learned over those decades in a paper published in December in the Journal of Medical Entomology.
The ticks given to Shepherd back in 1976 were Argas brumpti—a soft tick native to the more arid parts of eastern and southern Africa. Americans are more familiar with hard ticks, which have a hard dorsal shield (or back, roughly), tend to feed for a long time, and swell mightily after a meal. “The soft ticks,” says Shepherd, “can also bloat but not as extremely as the hard ticks, and they take many short, fast meals rather than meals that last over several days.” Argas brumpti is a large tick, the females ranging up to 20 millimeters (0.75 inches) long. In their native range they tend to hang out in places where they are likely to find food: burrows where animals sleep, dust baths, or termite mounds where animals come to scratch themselves. Little research has been done on A. brumpti, perhaps because it causes no known diseases, but Shepherd’s long observations provide some astonishing insights into what a tick can do.
Shepherd kept his ticks at 21 degrees Celsius and 81 percent relative humidity, optimal conditions for these ticks. Although the temperature and humidity were kept constant—feeding was not. In the early days after acquiring his A. brumpti cohort, Shepherd let them feed on rabbits in his lab. He says he didn’t like doing this because it was “awkward for the rabbits.” Starting in 1984, Shepherd no longer had a ready food source available, so he stopped feeding the ticks—for eight years. Despite this, some of his first batch of ticks survived, living for 27 years.
This longevity, Shepherd writes, “is apparently a record for any species of tick.” It’s a particularly stunning achievement when you factor in the eight years of starvation. And it was no fluke. Some of the offspring of those ticks are still going after 26 years. That some ticks can live for decades is a useful piece of information to learn from a random gift—but it’s not the only surprising discovery Shepherd’s A. brumpti provided.
Halfway into the eight-year feeding hiatus, the last male tick died. Nevertheless, after feeding resumed for the remaining females (with the first feeding on Shepherd himself), at least one of the females produced batches of eggs that hatched to both male and female offspring. Shepherd says that parthenogenesis (asexual reproduction) is rare in ticks like A. brumpti and thinks it is more likely that these offspring indicate very long-term storage of sperm. Shepherd says research on other soft ticks shows that they do store sperm until they’re fed, at which point the sperm move up the reproductive tract and fertilize eggs. “That was only over a few weeks,” he says. “But at least it shows that they do store them until they get a good blood meal, and so apparently that’s what my ticks did—except it was four years.”
For Shepherd, the information bounty provided by these ticks is coming to an end. He wrote in an email that he is aging out of tick research, but, thanks to this paper, his gift ticks will keep on giving. He is sending them to some South African researchers who are using DNA sequencing to explore the phylogenetic relationships among ticks. Shepherd says, “I admire ticks for their survivability and adaptability. They are so good at exploiting a niche where they just need to wait for a long time to get the next meal.”
And, for these ticks in particular, he says, “I think these ticks are an exceptional example of just being able to survive and hang out.”
Journal of Medical Entomology
Paige Embry is a freelance science writer based in Seattle and author of Our Native Bees: North America’s Endangered Pollinators and the Fight to Save Them. Website: www.paigeembry.com.