They are a native insect that naturally feeds on milkweed plants. If by "bad" you mean are they an invasive or pest species, then no, they are not bad. Some people are allergic to their hairs though, so be careful with them...
A Milkweed Tussock caterpillar is not poisonous. It belongs to a class of moths in the Arctidae family and is completely harmless to humans and animals.
Illinois has caterpillars that include the brown hooded owlet moth and monarch butterfly. Other caterpillars that are found in Illinois include the Asteroid, white-marked tussock moth, yellow-marked tussock moth, milkweed tussock moth, and the viceroy caterpillar.
Milkweed leafs
The rusty tussock moth (Orgyia antiqua)
Tussock moth caterpillars are relatively toxic to other animals. If a dog ingests one, it could get very sick from the poison.
The accepted scientific name is Euchaetes egle.
The small white caterpillars that you will commonly see on maple trees are called Lophocampa Caryae. They will turn into a Hickory Tussock moth.
Milkweed is eaten by several species of insects, most notably the monarch butterfly larvae, red milkweed beetle, and milkweed tussock caterpillar or tiger moth. In turn, monarchs are eaten by birds, and tiger moths by bats.
Caterpillars others than the monarch... there are only four types of butterflies that lay their eggs on milkweed: the Monarch Butterfly (Danaus plexippus); the Queen (Danaus gilippus); the Tropical Milkweed Butterfly (Lycorea cleobaea); and the Soldier Butterfly (or "Tropic Queen"; Danaus eresimus).Another caterpillar that I was desperately trying to find the name of (which brought me to this page) is Euchaetes egle, the milkweed tussock caterpillar or milkweed tiger moth.
Torolf R. Torgersen has written: 'Identification of parasites of the Douglas-fir tussock moth, based on adults, cocoons, and puparia' -- subject(s): Identification, Parasitic insects, Douglas-fir tussock moth, Parasites 'Douglas-fir tussock moth handbook' -- subject(s): Control, Douglas-fir tussock moth
a tussock moth
Richard R Mason has written: 'Douglas-fir tussock moth handbook' -- subject(s): Larvae, Douglas fir tussock moth
they can probably be located in all of America if you attract them you can attract them with milkweed I do not know what their favorite milkweed is but just try tropical milkweed that is monarch caterpillars favorite food.And do not use pesticide on any animals do not use that gypsy moth spray i mean do you think they know what their doing.And think about this their perfect they never sinned so do not use pesticide do not kill any animals I respect all animals even if their was a cockroach in the house I would not care.And if you want to attract painted lady caterpillars than use Canada thistle.Put the Canada thistle in a pot because the thistle will probably kill all the grass.and if you want to attract black swallow tail caterpillars plant parsley. do not kill any of the caterpillars and do not eat anything they are eating.And i would also like to tell you not to rip out flowers for yourself i mean do you know how wasteful that is.don't you want the flowers to live i mean its not like the only way to see them is to rip them out.let the bees go on them.and your killing the flower to i mean that is like killing a human because flower have male and female organisms i think.so do not rip out flowers that is horrible.