When a tick becomes engorged with blood, the sack it uses to hold the blood stretches and often takes on a silvery, whitish appearance; in such a case, it may be described as a white tick. It is the engorgement that causes the tick to appear white, which means a white tick isn't really a different kind of tick at all. Usually, the tick's sack is brown or black, but the engorgement of the sack causes the change in color appearance.
When a person sees a white tick, he might assume that he has sighted a different species of tick. This is due to the fact that most people are used to seeing brown or black ticks. A white tick, however, isn't any different from its brown or black counterparts; it is simply so full of blood that its sack has become overly stretched. The overstretching of the sack makes the sack appear white, especially grayish or silvery white, rather than its usual brown or black coloring. Often, this change in appearance occurs with a common tick called a deer tick.
People spending time in forested or grassy areas usually take measures to avoid ticks because they behave like external parasites, feeding off the blood of humans and animals. Usually, a tick attaches itself to a human host without making its presence obvious and then feeds off the host's blood, sometimes for days at a time. If a tick is able to remain undiscovered, he could stay in place and feed off the host for a few days. Eventually, the tick's sack becomes so engorged that a person who sees it might describe it as white. Interestingly, it is usually at this point that the tick releases its grip on its host and stops feeding.
After a tick has become engorged, he usually drops off his host. In some cases, the tick may then go into a hibernation-like state in which it does not feed for an extended period of time. In fact, some ticks can live for months or even years before feeding again.
White ticks, like those that have the normal black or brown appearance, are typically considered pests. This is due, in part, to the fact that they spread disease. For example, the deer tick is well known for spreading a serious infection called Lyme disease. Some ticks can spread more than one type of disease, however.