Arthropods, specifically in this case spiders! As geocachers I guess we are bound to come across a few in our travels. While most spiders are not dangerous to humans, some can deliver venomous bites that may cause harm. In New Zealand, the katipō and redback spiders are venomous, and white-tailed spiders can also bite, but their bites are generally not considered poisonous. Just be thankful we're not in Australia.
Cache is a bison. Log only, BYOP.