Several venomous caterpillar species that cause dermatological and allergic symptoms in humans by means of their toxic hair fibers can be found in the northeast US. Some of these medically significant caterpillar species include the Gypsy moth caterpillar, the browntail moth caterpillar, the lo moth caterpillar and several tussock moth caterpillar species. However, when it comes to puss moth caterpillars, which are said to be the most venomous of all caterpillars in the US, most envenomation cases occur within the southern states, particularly the southeastern states.

The term “puss moth caterpillar” is often used interchangeably with “flannel moth caterpillar.” The most venomous puss moth caterpillar species in the US is the Megalopyge opercularis, which is more commonly known as the “southern flannel moth caterpillar.” While this species is largely associated with severe envenomations in the south, the southern flannel moth caterpillar has also been documented in all northeastern states except for Maine. Southern flannel moth caterpillars are far more common in the south than in the northeast, but three other puss moth caterpillar species can be found in the northeast. Of these three northeastern species, Megalopyge crispata, or the “black-waved flannel moth caterpillar” is the most dangerous to humans.

The southern flannel moth caterpillar is considered a public health threat in several southern US states, particularly in Texas and Florida where school sessions have been canceled on account of this caterpillar’s abundance. The sting inflicted by these caterpillars produces a pain sensation that is often described as feeling like a limb has been suddenly amputated, and rare envenomation cases result in death. The black-waved flannel moth caterpillar that is abundant in all northeastern states is just as bad as its southern counterpart, as this species can cause lasting and excruciating pain, as well as systemic symptoms such as muscle spasms, seizures, shock, headache and respiratory distress. These caterpillars feed on numerous trees, making them common in public areas, particularly within parks, backyards and school playgrounds. Each island off the coast of Massachusetts is home to an abundance of black-waved flannel moths, and they pose a public health threat in Canada as well. These caterpillars are often found on tree branches and twigs, where children may feel inclined to pick them up. The black waved flannel moth caterpillar resembles a cotton ball, but as they consume more vegetation they develop darker spines that are orange-reddish in color.

Have you ever spotted a puss moth caterpillar near your home?