A few of the creatures we’ve run into on St Catherine’s Island, GA, during the Island Ecology class:
My Advanced Ecology and Biodiversity class continues its investigation of our local tick populations. A few weeks ago, we collected ticks in the field and preserved some of them in alcohol. We’ve now looked through these collections using microscopes. We collected only “seed ticks,” little animals that are barely visible to the naked eye, so this close examination lets us identify the life stage and species of each individual.
For anyone who has been attacked by a swarm of seed ticks, the view down the microscope is at first a little horrifying. These agents of suffering loom up at us, unlocking a shiver of fear. Several of us unconsciously reached down to scratch our legs as we looked through the eyepieces.
After a few minutes and, paradoxically, at higher magnification, the little creatures take on a certain rotund charm. The fact that they are pickled helps a lot. We can tell larvae (the first life stage after the egg) from nymphs (the stage that comes after a larva feeds and molts) by counting legs: six for larvae and eight for nymphs. If only all biological identification were so easy.
The majority of the ticks in our collection were larvae. These two are lone star ticks, identified by the shape of the mouthparts and the number of crenelations on the rear of their body (this feature is hard to make out, especially in home-spun photos like these — taken by holding a camera up to the microscope lens…):
Undoubtedly, the mouthparts are the most fascinating part of the animal. The two outer parts are the palps, used to feel around for a choice spot to drill. The inner portion is made from two knives and a barbed feeding tube. The knives, called chelicerae, open the skin. Then the tube, the hypostome, is inserted and cemented. The cement both holds the animal in place and serves as a gasket to stop leaking. The animal then spits a mixture of chemicals into the host to loosen up the blood. The ticks are fracking us for protein. Without the permission of the landowner.
Of course, when ticks feed, they may also transmit diseases such as Lyme, Rocky Mountain Spotted Fever, and Ehrlichiosis. In the case of Rocky Mountain Spotted Fever, the larvae may hatch already carrying the disease, having received it through the egg from their mother. But the other diseases are not transmitted through eggs. Instead, larvae become infected when they feed on mice and other vertebrate hosts. Larvae only feed once before turning into nymphs. So a bite from a larval tick is generally less dangerous to a human than a bite from a nymph or adult. The latter have fed on other vertebrates and are more likely to carry disease. Good to know, but little comfort when your legs are aflame with the itches of a hundred bites.
My students are currently extracting DNA from the animals to confirm our identifications and to test for diseases. I’ll keep you posted. In the meantime, remember to tick check. These diseases are a reminder that parasitism and disease are ubiquitous components of the ecology of our world.
It seems that my previous post about monstrous numbers of ticks near Lake Dimmick echoed a very old pattern. My friend Lizzie Motlow reminded me that the old name for the Lake Dimmick area is “Tick Bush.” Readers familiar with Sewanee history will remember that Ely Green’s autobiography from the late nineteenth and early twentieth centuries features a number of encounters with residents of the Tick Bush area. I had not, until now, known the exact location of Tick Bush.
Jerry Smith and Sean Suarez’s Sewanee Places corroborates this Acarine geography. They write that Tick Bush was down the hill from “Summit” or Midway. The two locations even had different schools. Smith and Suarez’s account places Tick Bush close to the present day airport, just two thousand feet upstream from where Lake Dimmick is located.
I think we can now say, with the confidence that comes from replicated quantified samples, that Tick Bush remains firmly planted on the map.
Now for some relief from discussions of ectoparasites… Ticks were not the only animals in evidence. The following male Black Swallowtail was nectaring on the thistles in the University’s cattle pasture. His beauty is a nice antidote to the creepiness of the skin-crawling masses emerging from Tick Bush’s bushes.
My “Advanced Ecology and Biodiversity” class has been surveying ticks in and around Sewanee. We’re documenting which species live here, where they live, and what their relative abundance is in different habitats. So far, the hands-down winners for numbers of ticks are the cattle pasture and adjacent wooded roadsides near Lake Dimmick. In one twenty meter sample, we found nearly six hundred small ticks.
We sample by dragging a canvas cloth over the ground, then counting the ticks that have latched onto the cloth. This simple method is the standard protocol for assessing tick populations. These “tick drags” go very quickly when we encounter few animals, but when a seed tick “bomb” hits the cloth, it can take half an hour to pick off all the minute crawlers.
We’re storing the ticks in vials of alcohol. We’ll identify them later on in lab and we may also extract DNA to assess whether any of the ticks are carrying disease. We discovered today that when shaken the vials make snow-globe like ornaments. We’ll be marketing these as rustic woodland souvenirs.
As part of the class, students will be producing a pamphlet on the ticks and tick-borne diseases of Sewanee. I’ll pass it along through this blog when it is ready. For now, I recommend not rolling around in the cattle pasture at Lake Dimmick. The lawn around Stirlings coffee shop appears to be much safer for that kind of activity. (For real: we found no ticks there; Abbo’s Alley, on the other hand, had a few.)