* By number of species: This is the most common way to think about "largest." Here, the bacteria (also known as prokaryotes) are the largest group, followed by the insects (which belong to the arthropods). So, insects would likely be the second largest.
* By total biomass: This considers the total weight of all individuals in a group. While bacteria are extremely numerous, their individual size is small. In terms of total biomass, plants (Kingdom Plantae) are likely the largest group, with bacteria coming in a close second.
* By taxonomic rank: You could consider the "largest" group based on how they're organized. The domain is the highest taxonomic rank, so Bacteria would be the largest group, followed by Archaea (another domain).
Therefore, without a specific definition of "largest," it's impossible to give a definitive answer.
To get a more accurate answer, you need to clarify what criteria you're using to define the "second largest group."
