Ticks are related to spiders and mites (they're all Arachnids). They transmit several serious maladies to humans including Lyme Disease and Rocky Mountain Spotted fever. Currently there is a transition taking place in the Northeastern U.S. where the deer tick is being replaced by the Lone Star tick. This is primarily due to hotter and drier conditions that are developing as woodlands and other natural settings are replaced by concrete and blacktop.