The common term for this is mimicry. Take as one example - the similarity in the patterning of one of the sub-species of milk snake, which closely resembles the banded markings of the coral snake. The milk snake is completely harmless, while the coral snake is highly venomous.
An antonym for harmless is harmful.
Every animal has something they add to nature, they can also cause problems. Chipmunks are generally harmless, however, they can be harmful to gardens and plants. They can be harmful if harassed and bit out in retaliation.
no they are harmless
they are only harmful to humans if you attack their home and try to eat them.
harmful
Innocuous, harmless
harmful, destructive, evil
No they are harmless to humans
Black magic
Without animal testing, humans would have a greater risk of dying if expirementing with products that people have no idea whether it is harmful or harmless. Personally I don't agree with animal testing, but what other choice do we have?
The harmless animal passed by.
Stray dogs are quite harmful.