Tiffany Terp

Hide and Seek? Or Hide and Quest?

 Like stated earlier, deer ticks are blood feeding parasites of mammals, birds, and reptiles.  In order for the ticks to feed they must come in contact with their host. Ticks seek host in many different ways, but deer ticks do so in an interesting behavior called questing.

Additionally, there are two basic strategies used by arthropod vectors for finding hosts, passive and active.  Species that engage in passive, such as the deer tick, remain in their habitat and wait for their host to come to them. Active species leave their habitat in search for their host.  The deer tick waits in the environment hoping for direct contact with their species walking by, ambush strategy.  Ticks, living in grass, herb, or brush covered habitats climb the vegetation and wait for a host to brush against them allowing them to grab on.  Vibrations, odors, body heat, shadows and CO2 given off by animals/host initiate ticks question pose.  Once a host is detected the tick extends and waves its forelegs rapidly waiting for contact. If contact is made the tick clings to the host’s body. 

The height at which ticks quest is influenced by the host size they are seeking.  This is usually strongly correlated with the life cycle stage they are occupying. Nymphs usually quest on lower vegetation such as brush nearer to the ground because their targeted host is usually smaller animals such as mice, squirrels and birds. Likewise, adult ticks are normally found in higher vegetation about a meter off the ground because they target larger animals as hosts such as deer. Some ticks can be found near brush and larger trees such as maple or pines trees.  Questing height is by no means the sole determinant of host specificity.  The availability and abundance of hosts also play a role on the host chosen. White-footed mice and white-tailed deer are very available and therefore, is the reason that they are two of the more common hosts found to have aggregated ticks on them. Another factor that influences host selection is surface area.  The animals with the greatest surface area are also found to have large amounts of tick invasion.

Deer ticks are characterized as generalists who are found under the opportunist category meaning that they are not host-specific and will feed on a wide range of vertebrates within their questing height. However, even generalists are known to reject some animals as hosts. More specifically, deer ticks have evolved a highly effected range of pharmacologically active agents in their saliva which are used to suppress the defense mechanisms in their host.  This behavior decreases the chance for host rejection, however the saliva of deer ticks does not have the capability to suppress all animals defense mechanisms and therefore is considered somewhat host-specific. For example, the deer tick’s saliva, that is ejected while feeding, has active agents to prevent edema, inflammation and vasoconstrictions of its host. With this, it is able to suppress the immune response of the white-footed mouse. However, their saliva does not contain agents to avoid histamine-induced edema, a mechanism present in the guinea-pig and therefore cannot use the guinea-pig as a host because the guinea-pig will be able to detect the tick and reject it. Lastly, macro and microhabitat distribution also influences host selection. Ticks adapted to a specific habitat will feed on animals that are also adapted and found in the same habitat. This again, is one of the reasons deer and mice are the most common hosts found in the tick’s lifecycle.

Once the tick has come in contact with a passing host it grabs on and then begins its feeding process first by securing its attachment. To begin, the tick pierces the skin, with the aid of the cheliceral digits. The cheliceral digits do not have the ability to rotate or pronate and therefore only use horizontal cutting actions to tear the epidermis. Then it inserts its hypostome, which is the first mood of attachment, into the host’s skin. (The structures of these mouthparts are described in more depth in the adaptations section.)  Then it proceeds to cut the capillaries and other small blood vessels generating blood flow to the wound site. Again, like stated above the tick has to suppress the host’s homeostatic response by pharmacodynamic mechanisms in their saliva.

Like stated earlier, humans can also be a host for the deer tick. Just like the other animals if a human walks by and is detected by a questing tick the host can and will grab onto the skin of a human. It can then crawl on the human to a more secluded area on the humans body.  The same attachment and feeding mechanisms are seen on humans. If a human spots the tick there are a few ways to get the tick to detach. There are many “folk” methods of getting the tick to “back out” from the skin, however it is very important you do this in the proper way to make sure you get all of the mouthparts out of your skin.  If you remove the tick improperly, there is a good chance the hypostome is still under your skin and cause further irritation and infection. The other reason it is important to properly remove the tick is because you do not want to crush the tick while inside your skin, if the tick is infected with Lyme Disease it can be transmitted to the human if crushed.  The “myth” stating to cover the butt of the tick with nail polish or rubbing alcohol is shown to be ineffective. As well as the “myth” to light a match stick, blow it out and touch the butt of the tick. The most effective way to remove a tick it to use a forceps or household tweezers to physically pull the tick out. It is very important to place the tweezers as close to the skin and mouthparts as possible. Then with a steady tugging motion the tick and its mouthparts should detach from the skin, do not twist or jerk the tick. If located in an area with Lyme Disease, it is encouraged to take the tick to a physician.