Attack it.

You have to get this thing off of you ASAP. You bring up one hand in a fist and start trying to awkwardly punch at the thing over your shoulder as it seems to be pretty much spread out over your entire back, with its legs clinging tightly to your torso.
The bug's tough carapace seems to absorb most of the damage from your weak punches, but it does seem to get "annoyed" in a way as you hit it.

Its front two legs suddenly spring open, pulling away from your breasts to try and 'capture' your arms. One leg quickly pulls your other arm out from under you, causing your face to drop to the dirt as you let out an "oof!" sound and instinctively close your eyes and turn your head to the side. It wasn't hard for the creature to then grab your other arm as well, and quickly pull both to your sides where its legs hold them tightly against your body.

Just as you start to panic, you can feel a sharp 'pinch' on the back of your neck as its mouth slides down to nip at your skin, causing some of that strange goo its mouth was dripping to sink in. Suddenly, your skin in that spot starts to grow very hot, and the warmth spreads quickly throughout your body as it seems to be 'arousing' you. I appears the beetle hit you with a very potent aphrodisiac, likely meant to 'subdue'. Your muscles start to feel more relaxed as your soft sex-lips start to puff up and glisten with your growing arousal.

Suddenly, you can feel something like a 'thick' tube nudging against your puffy cunny lips, rubbing against them slowly. You quickly realize this was the 'tube-like' appendage you saw on the creature before it attacked. The appendage seems to have extended outward and curled up under your panties where it was now stimulating your sex. The stimulation from that tube sends delightful chills of pleasure up your spine, and even more so when you feel some kind of 'slime' splatter against them that causes them to become even more hot and swollen with arousal.

There's really only two options at this point, as you can't move. You obviously don't want to this bug to have its way with you... or do you? You can call for help, or you can relax and try to enjoy it.