First of all, when we say that these bugs use shields, you might assume that means they're born with a hard shell, but as larvae they actually start out just as squishy and vulnerable as a month-old banana. So, they have to quickly learn to overcome this little inadequacy by building crude shields out of their own dead skin and feces to wield against predators. Let's say that again: The tortoise beetle larva protects itself from danger by swinging around a poop shield.
Known in proper entomologist terms as the "Dude ... gross" strategy.
But even the advanced shit-on-a-stick approach to protection isn't always enough to safeguard the beetles, so some larvae came upon the brilliant idea to band together and join their shields to create an impenetrable barrier of +5 protection and +10 total gross-out. Their version of this phalanx strategy is known as cycloalexy. The guards keep their fecal shields turned outward, while the feeders inside the circle keep their shields held overhead. When something gets too close to their defensive barrier, it usually gets the crap beaten out of it by the bugs' crap cudgels.
The best defense is a good offense, and it doesn't get much more offensive than shit bludgeoning.