A parasitic relationship begins when one organism, the host, provides a food source or shelter for another, the parasite. There are three types of parasitic bonds. Parasitism is when only the parasite benefits and the host is the sole provider. In the Mohave Desert, a flea acts as a parasite on the desert coyote by taking blood for sustenance. In this parasitic relationship, the flea benefits, but the coyote loses blood, bears discomfort and suffers potential disease.
Commensalism is a relationship where the parasite benefits while the host neither gains nor loses. For example, to protect its young from predators, a cactus wren builds its nest in a host cactus.
Mutualism is a connection resulting in both host and parasite being winners. For example, a honey bee uses a flower to gather its food while the flower experiences the benefit of pollination.
A hemiparasitic plant, the desert mistletoe for example, has photosynthetic leaves deriving oxygen on its own but depending on a host for nutrients. A holoparasitic plant, such as dodder, depends completely on its host. Some stem parasites are endoparasitic and live entirely within the stem of a host.
Birds help plant parasites find their hosts. A flycatcher eats mistletoe berries and passes undigested seeds in droppings to host trees.
Sometimes root parasite seedlings such as the sand plant find a host buried deeply in the sand. Dr. Job Kuijt, in "The Biology of Parasitic Flowering Plants," explains that the sand plant sends out pilot roots to search for a host shrub. The pilot roots then project haustorial roots which connect and penetrate the host.
The insect and animal world contributes when harvester ants or kangaroo rats burrow below the sand dunes beneath host shrubs and deposit the seedlings.
A desert parasite such as sand food can weigh several times more than its desert host, 106 pounds versus a meager one pound.
The world's largest flower is a parasite. The Rafflesia arnoldii is 3 feet in diameter.
In 2007, Chagas' disease, a blood-borne parasite, made the news. The disease is spread by an insect which bites unsuspecting humans and animals. Millions of people in Latin America could have Chagas' disease without suspecting it. According to the U.S. Centers of Disease Control and Prevention, this potentially fatal disease is rarely seen in the United States, but immigration from other countries may become a threat. Desert blood banks are encouraged to test for it.
