Tag Archives: tick

Itch, magnified

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…):

We also found a few dog tick larvae. Note the different shape of the mouthparts:

Nymphs were much less abundant, although we did find a few. The following is a the nymph of a lone star tick (the hindmost pair of legs is tucked in, but you can see them if you look closely).

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.

Scratch, scratch.