This creature can be easy or more difficult to catch, depending on your luck. You don’t need a Ghillie Mantle, and you don’t need to look for another creature on whose back this bug is riding; this target’s location is static. Unfortunately, your target’s schedule is erratic, and it’ll only appear during the dawn and the dusk.
First, the location. Travel to the Northeast Camp in the Coral Highlands, crawl out through the hole to the west, turn north and drop off a cliff to the north, then drop off another cliff to the west, and finally jump off a third cliff to the south. On the lowest part of AREA 10, turn west and crawl through a hole, then follow the linear path ahead until you reach a waterfall-fed pond. At this water, turn north and follow the stream northwest until it converges with another stream before finally running off a cliff. Where the stream you followed unites with another, turn northeast and head up a ramp and follow the path as it winds around some large mushroom-like plants. On the northern end of larger mushroom you may find your target - a Prism Hercudrome. If your insect isn’t there, you’ll have to return after some time has passed - traveling between maps should do the trick.
Once you find it and net it, you’ll earn this trophy/achievement.