We all have likely seen at least one monarch butterfly flying around the garden over the course of the summer, or perhaps we have spotted monarch caterpillars on milkweed plants. If you look closely at those milkweed plants, you might have seen a few other brightly colored insects on the plants as well.

Plants can be useful for generating chemical compounds ranging from flavors to pharmaceuticals. The milkweed seen outside is not too useful to us. Its main chemical claim to fame is a compound known as cardiac glycoside. This compound can make us and our pets sick if ingested.

Several plants produce cardiac glycoside—milkweed perhaps being the most well known. Some insects feed on these plants and are unaffected by the cardio glycoside; nature has given these insects a form of chemical warfare to be used against would-be predators due to the sequestering of cardiac glycoside in their bodies.

The images in this column show a few of these insects. Their bright markings say to predators, “Caution, do not eat me!”