The Carlisle Mosquito Online

Friday, May 31, 2002

Features


Ticks

Name: American Dog Tick (Dermacentor variabilis) and Deer Tick (Ixodes scapularis, same as Ixodes dammini). The Deer Tick is also known as the Black-legged Tick. Both dog and deer tick could also be called "nasty little suckers."

When and where found: Early spring through late fall, in grassy meadows, in the woods (especially where deer are numerous), on your dog, or crawling up your pant leg. I find Scotch tape very useful for removing ticks that are not yet attached, and extremely useful for containing them after removal ­ just fold the tape over on itself.

Friends and relations: Ticks are in the arachnid class along with other eight-legged arthropods like spiders and scorpions, making up a trio for the next-to-be-named axis of evil. There are about 300 species of ticks around the world. There are soft ticks with leathery skin and a downward-facing head on the underside; and hard ticks, like the dog and deer ticks, that have a hard dorsal plate and a forward-facing head. The Lone Star Tick (Amblyomma americanum) is a hard tick common to the south and west of us but expanding its range northward. Last year one turned up in Carlisle during Biodiversity Days in June.

Distinguishing characteristics (both species): Tear-drop shaped, with four pairs of legs and piercing mouthparts. There is no external distinction between head and abdomen. The ticks are flat and dark brown before feeding, and bloated and a dull gray after feeding.

Deer Ticks: The female Deer Tick has a black dorsal shield and a reddish brown body while the male is dark brown to black all over. The adults are tiny, about a sixteenth of an inch wide and an eighth inch long; only one at a time can dance on the head of a pin.

Dog Ticks: The adult Dog Tick, unfed, is about twice the size of the Deer Tick. The female Dog Tick has a pale colored dorsal shield with brown markings and a dark brown body. The male has a brown body with symmetric whitish markings.

Behavior: All ticks are external parasites that feed on blood. They use modified jaws to cut the host skin; then they insert a feeding tube equipped with several rows of barbs that keep them firmly connected to the host. Female ticks drop off the host animal after feeding and lay thousands of eggs which hatch into six-legged larvae. The larvae molt into eight-legged nymphs which subsequently molt into adults. A blood meal is required for the tick to move to the next stage of its life cycle.

Disease: Dog Ticks are not a vector for Lyme disease but they may transmit other diseases like Rocky Mountain Spotted Fever. Both male and female Deer Ticks, and other ticks in the genus Ixodes, can transmit Lyme disease. In the Northeast, the Deer Tick is considered the most important vector for the Lyme disease bacterium, a spiral-shaped organism called Borrelia burgdorferi which exists in a variety of reservoir hosts of which the most significant is the White-footed Mouse. The primary acquisition of the bacteria by ticks occurs at the larval stage which means the resulting nymphs and adults are already infected and can pass the bacteria to new hosts such as other mice, and larger mammals like dogs and humans. While adult Deer Ticks have been found on at least 13 species of mid- to large-sized mammals, the preferred host is the white-tailed deer. The Lone Star Tick carries Lyme disease, and also ehrlichiosis.

References: Spiders and Their Kin by Herbert and Lorna Levi; University of Michigan, Museum of Zoology, online at http://animaldiversity.ummz
.umich.edu; the Tick Research Laboratory at the Rhode Island Agricultural Experiment Station, online at http://www.riaes.org/resources/ticklab/ticks.html


2002 The Carlisle Mosquito