Black Death (Nuclear Polyhedrosis Virus) in Monarch Caterpillar (Danaus plexippus)

This caterpillar looked almost as bad as the milkweed leaf. It is infected with NPV (Nuclear Polyhedrosis Virus) and will soon die. I can tell that it's infected because the dark bands are wider than usual. Also, the antennae are shriveled and the caterpillar was mostly unresponsive and lethargic.

This virus enters the nucleus of infected cells and reproduces until the cell begins to produce crystals in the fluids of its host. The host becomes swollen with virus-containing fluid, turns black, and dies.

Habitat: Milkweed in a meadow