Ticks are external parasites that feed off of blood as their main food source. Although many believe that ticks are insects they are actually arachnids, like spiders. There are many different species of ticks that are divided into two main categories: hard ticks, such as the common dog tick, and soft ticks. The physical appearance of ticks varies by geographical location but in general they have eight legs and range in size from 2-3.5 mm.