Dark Banquet - Bill Schutt [87]
On the other hand, the hard ticks are considered “field ticks” because that’s generally where they attack their hosts. These are also the ticks we hear the most about, which is no surprise since they’re the ones responsible for transmitting pathogens that cause Lyme disease and Rocky Mountain spotted fever.
Animals often pick up ticks and chiggers when they sit or lie down in an infested area. The parasites use a combination of visual, chemical, and tactile (touch) cues to close in on their victims. Additionally, both chiggers and ticks can catch a premeal ride when their potential prey brushes against the grass or leaves where the parasites have been clinging with their crablike limbs. This works in the following manner.
When an animal moves through high grass or brush, it causes physical disturbances to the environment as it tramples and displaces the soil and vegetation in its path. Ticks and chiggers take advantage of the vibrations produced during this process. Both show strong inclinations to climb upward—and the result is that they spend much of their hunting time perched at the tips of grass blades, sticks, and other objects located close to the ground. They also congregate along the outer margins of leaves belonging to weeds and other low-lying plants. When these substrates vibrate (owing to a physical disturbance like that produced by the movement of a nearby animal), both chiggers and ticks respond by lifting and waving their two front legs. This “questing” response increases the likelihood that the parasite’s legs (which bear an array of Velcro-like spikes, hooks, and bristles) will make contact with a potential host as it passes by. Once the initial contact occurs, ticks employ all eight of their legs (six in chiggers) to haul themselves onto the unsuspecting lunch wagon.*133
Dr. Yeh pointed out a behavioral difference related to questing that seemed to spell even more trouble for those seeking to avoid encountering these parasites.
“Around here, black-legged ticks generally quest in the early morning, when it’s not too hot and dry for them. Because Lone Star ticks prefer the heat, they quest in the afternoon. Unfortunately, that’s when they’re most likely to encounter people.”
As far as speed goes, ticks are far slower than chiggers—slower moving, slower to bite, and slower to drop off after a bite. Additionally, unlike chiggers, which usually make a mad dash for your socks or belt line, once ticks have hitched a ride, they walk around the surface of their host’s body (often for hours) using thermal and chemical cues to search for a suitable feeding site.
Some ticks, like those that prey on humans, aren’t particular about who or where they bite, while others are highly specific. For example, the larval instars of Rhipicephalus evertsi, a tick that preys on bovids (cows and their cud-chewing relatives), prefer the ears of their host while the adults of this species show a strong preference for attaching themselves around the anus.
The cold tolerant tick Dermacentor albipictus thrives in the northern latitudes. In regions like western Canada, it’s responsible for Winter Tick disease in large ungulates like moose. These hoofed giants become so heavily infested with ticks (sometimes numbering nearly two thousand per individual) that they spend much of their time grooming themselves and incessantly rubbing against trees. The resulting hair loss (up to 80 percent in some cases) gives the stricken moose a gray or even white appearance instead of their normal dark brown color and has given rise to the term ghost moose. These animals are often emaciated from blood loss and exposure, and since their feeding behavior is severely disrupted, they also exhibit loss of stored body fat.
Tick bites, and their behavior afterward, also vary significantly from what is seen