Tiny acanthocephalan, or thorny-headed, worms kill about 14% of sea otters. Otters become infected after eating sand crabs and spiny mole crabs that harbor the intermediate life stage of these worms. In heavily infected otters, the worms burrow through the walls of the otters’ intestines, set off a painful inflammation that ties the intestines in knots, and the otters die. This disease is most common in juveniles. Sea otters also succumb to a variety of bacteria and a fungus, Coccidioides immitis, that causes valley fever or coccidioidomycosis. Otters are infected the same way that humans are – by inhaling fungal spores in dust from the state’s dry interior valleys.