It might seem silly that they are wasting their latex to protect their latex tree, but there are worst things that real animals do in real life, like grow colorful plumage to get the attention of both potential mates and whatever want to eat them, or squirt blood out of their eyes to scare off predators, or removes their own limbs and throw them at their opponents to escape. If The Dark Forest monsters seem weird to you, you need to learn more about real world fauna and flora :P
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Small Edit: Added the missing tails