First get a harpoon gun with the net projectile. Find a rhyniognatha, preferably a low level, and kill it. Take the pheromone to use on your large dino. Find another rhyniognatha and shoot it with the net. Using a magnifying glass and your sword, get the health really low, get on your dino and use the pheromone in the large dinos inventory. Wait a bit and your dino will get infected with the rhyniognatha’s larvae.