There is a Fava Bean plant in our sidewalk bed that is covered with aphids. It looks awful! There are LOTS of other Fava Bean plants in the front yard without aphids. One plant has them. Why not pull it out? Well, there is good reason....
On closer look one will find an entire ecosystem in action. All of it existing on one plant. First to show up were the aphids. They started sucking the juices out of the plant and excreting a syrupy substance on the leaves. Then, lots of different aphid-eating insects appeared and went to work gobbling them up. At one point little yellow eggs appeared on the undersides of some leaves. I had seen adult ladybugs among the other hungry insects so I waited to see if the eggs belonged to them. Ladybug larvae eat aphids in large quantities so that plant would be a perfect spot to lay your eggs if you were a ladybug!
Sure enough, little prehistoric looking creatures appeared all prickly in orange and black dots. Those colors are these babies protection. Even though they look prickly they are actually quite soft-bodied. In nature the colors orange and black represent something that is inedible. The Monarch butterfly is the best example of this. They taste horrible to birds so many, many other butterflies use those same colors for protection even though they might be quite tasty.
So, if you see these little larvae do not be alarmed. Be happy! They are important helpers in your garden. Each day I transfer some to the fruit trees in the back garden to eat the aphids appearing on the new leaves. It's working!