The insects on the cover of Programming Embedded Systems with C and GNU Development Tools, Second Edition, are ticks. There are approximately 850 species of these small to microscopic, blood-feeding parasites distributed worldwide. They are particularly abundant in tropical and subtropical regions. There are two main families of ticks: hard ticks, whose mouth parts are visible from above, and soft ticks,whose mouth parts are hidden.
In both hard and soft ticks, the mouth is made up of three major parts: the palps, the chelicerae, and the hypostome. It is the hypostome that is inserted into the host's skin while the tick is feeding. Aseries of backward-facing projections on the hypostome make it difficult to remove the tick from the skin. Most ticks also secrete a sticky substance that glues them into place. This substance dissolves when the tick is done feeding. Their external body surface expands from 200 to 600 percent to accommodate the blood that is ingested.
Ticks go through three life stages: larva, nymph, and adult. At each stage they feed on a mammal, reptile, or bird host. Ticks wait for a host by perching on leaves or other surfaces with their front two legs extended. When a host brushes up against them they latch on and attach themselves. Adult female hard ticks lay a single batch of thousands of eggs and then die. Adult male ticks also die after a single mating.
As parasites go, ticks can be very nasty. They transmit more disease than any other blood-sucking parasite, including Lyme disease, Rocky Mountain spotted fever, and relapsing fever. They can also cause excessive blood loss. Some ticks secrete nerve poisons that can potentially cause death. Atick can be removed from skin by grasping it with a tweezer or a special tick-removing device as close to the skin as possible, and pulling in one steady motion. Do not squeeze the tick. Immediately flush it down the toilet—or place it in a sealed container and hold onto it for one month, in case you develop symptoms of a disease.