Biological pest control predatory midge "Feltiella acarisuga", and a ladybird "Stethorus punctillum". The bug "Orius insidiosus" has been successfully used against the two-spotted spider mite and the western flower thrips ("Frankliniella occidentalis"). Predators including "Cactoblastis cactorum" (mentioned above) can also be used to destroy invasive plant species. As another example, the poison hemlock moth ("Agonopterix alstroemeriana)" can be used to control poison hemlock ("Conium maculatum"). During its larval stage, the moth strictly consumes its host plant, poison hemlock, and can exist at hundreds of larvae per individual host plant, destroying large swathes of the hemlock. Not all biological control agents are directed at
What Is and What Should Never Be descending riff [of "What Is and What Should Never Be"] is amazing: It's like a bow is being drawn back, and then it releases. The rhythm of the vocals is almost like a rap. It's insane — one of their most psychedelic songs." This was also one of the first songs recorded by the band for which Robert Plant received writing credit. According to rock journalist Stephen Davis, the author of the Led Zeppelin biography "Hammer of the Gods: The Led Zeppelin Saga", the lyrics for this song reflect a romance Plant had with his wife's younger sister. "What Is