A northern tent caterpillar (Livrée du nord), Malacosoma californicum pluviale (Dyar), killed by a native nuclear polyhedrosis virus.  As exemplified here, the condition is commonly known as “hang-down disease”. Soon, the exoskeleton will burst, releasing the virus to be ingested by other larvae and contributing to the characteristic dramatic collapse of outbreak populations.  Idaho.
[Photo by Malcolm Furniss]