Menstruating monkeys were at risk from predators. As they'd swing through the jungle, their vaginas squirting - and monkeys do squirt - they'd leave a trail of blood. All a monkey's natural predator (a bigger monkey?) needed to do was follow the blood, noting the direction of splatter so they didn't go away from the monkey, and they'd soon come across tasty monkey goodness.
Monkeys learnt quickly. (Strange how dead thangs can learn, but that's just the mystery of nature I guess). Tampons. Ain't no tampons in the jungle so they used sticks. I don't know if you've ever seen a tree in the rain, but it doesn't tend to absorb much water. It's the same with sticks and blood: they don't absorb as much as whatever it is tampons are made of - bread? Menstruating monkeys have to pack themselves full with sticks. The sticks absorb a little of the blood, but mostly they just trap it and allows it to clot. When the sticks are full up, the monkeys tear the scab free from their girl thingies, and throw away the congealed plug. Predators can't chase that.
Man sucks. Poachers have watched all the nature films of monkeys shoving bundles of sticks up their cunts, and have used this information. Now they whittle tampons to the shape of a stick, paint them brown by dabbing them with a very dry brush, as if they were stencilling, and then chuck these stick tampon things around the jungle.
Cue a bleeding monkey. "Ooh, stick time. I'll have that one, and that one, and that one. I'll just scrape the lichen off that one, and it'll be fine. Just one more and I'll be full. Ooh that one's got a string sticking out of it, I'll go with that." Squirty squirt, bleedy bleed, absorb, expand. Expanding tampon in very full vagina equals pain, equals monkey grasping its bits in agony, equals monkey falling to the jungle floor, equals monkey cracking its head open on a very pointy ant. The poachers just pop round once a day and pick all the monkeys up. Sure it's ingenious, but soon there won't be any monkeys left, man.