Processionary caterpillars are well-described threats to human and animal health. They are found throughout Central Asia, Northern Africa, and Southern Europe. However, US military personnel may not be familiar with the threat that these organisms pose in Australia. The larval form of the bag-shelter moth (Ochrogaster lunifer) is a processionary caterpillar that has been found throughout inland and coastal Australia. These organisms are habitually associated with Acacia and Eucalyptus trees and they tend to form long chains known as "processions" as they travel between nesting and pupating sites. They are covered with numerous hairs that can detach, become airborne, and cause potentially life-threatening inflammatory reactions and ocular trauma in susceptible personnel. They can also cause severe inflammatory reactions in military working animals. It is important that military and preventive medical personnel become aware of the presence of processionary caterpillars in Australia, and that they can identify aerial or ground-based nests so that these dangerous organisms can be avoided by both humans and animals. Early identification is important so that prompt medical treatment can be rendered in the event of an accidental exposure.