We see them all spring and summer, and they sort of make you smile, these busy little beetles, all pretty and friendly. Except, how friendly are they? Back in the early 1980s, a local municipality always had us treat the aphids in the trees that overhang the city pool. One year, they opted instead to purchase ladybird beetles and release hundreds into the trees to control the aphid using a natural method.
In theory, it was a great idea. Those hungry little meat-eaters ate aphids by the thousands, and within a few weeks had the situation well in hand. In fact, they completely eliminated their food supply, and not willing to go hungry, they began biting the children in the pool! We were then reluctantly contacted to "see what we could do" about the problem of angry ladybird beetles attacking the kids.
Voracious predators, most species are fantastic at search-and-destroy methods versus aphids and mites, both of which can cause your plants extreme stress and death. Provoked, they can deliver a nasty pinch to a human as well, but it's not very common.
Once we see the larvae chomping away on the aphids, leafrollers, and other damaging insects, we explain that they're doing a good job, organic solutions, yadda yadda yadda. Sometimes, however, their presence is too little, too late. If the tree is truly stressed from a late-summer aphid attack, the hearty beetle may be unable to catch up to the aphid population, and a well-timed systemic injection can then kill the aphid just as the larvae pupate, meaning the aphid will die before the majority of ladybird beetles emerge as adults.
So if you see this battle-hardened larvae on a leaf on your tree or your garden, let it continue fighting the good fight in the perpetual eating contest that defines this predator.