Terrestrial urchins have long been known in Russia but these are some of the first found in Korea.
The AAAS (American Association for Advancement of Science) Science Journal article can be found here (registration required for the full article).
I have been (un)lucky enough to sight some myself. Just as with coral reef infestations, first you find one:
Then you find blooms of them.
I do not know if these are actually poisonous as many of their aquatic relatives are. In fact I could find little information about them. Local farmers and orchard owners obviously should use caution. Foxes are natural predators of urchins and possibly raccoon-dogs are as well. Perhaps this threat might be a boon for other native wildlife if they are re-introduced to combat the menace.
At Enchanted Learning, I found this diagram of sea urchins.