So you’ve created the perfect butterfly garden. You’ve got nectar available spring through fall (or winter if you live in a warm climate!). You’ve planted your garden with lots of native species that are attractive butterfly host plants, and included vertical, textured surfaces for the pupae you hope will soon populate your garden. Sounds like butterfly paradise, right?
Not necessarily. Butterflies have a lot of natural enemies, and they suffer a lot of mortality at every single life stage. This makes sense- a female butterfly might lay between 20 and 100 eggs in her lifetime. If they all survived to adulthood we’d be overrun (this might not be that bad, actually…). Predators, diseases, and parasites are all part of a natural, healthy ecosystem. It’s how nature keeps population size in check. In the case of butterflies we typically think of the threat from predators like birds, spiders, or lizards. But chances are good that mortality at other life stages actually plays a more significant role in the survival of most butterfly species.
Eggs are tiny, inconspicuous, and fragile. They can easily be trampled by larger animals, eaten inadvertently by larger herbivores, or succumb to fungal infections. Caterpillars can be eaten by predators, become infected by fungus or pathogens, drown, dry out, or become infected by parasitoids. Pupae can be knocked loose from their hold, be crushed, or succumb to fungus, pathogens, or parasites. Animals at all life stages can be destroyed by severe weather, including heat, cold, sun, rain, wind, or other abiotic forces like fires.
Out of all of these threats, the one I personally find the most fascinating is the threat posed by parasitoids. Like a parasite, a parasitoid spends a significant portion of its life cycle living inside or attached to the body of another organism. Parasitoids, however, typically consume and kill their host. Charles Darwin found the existence of parasitoid wasps so troubling that he once wrote in a letter that “I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars.” His concern was justified- many parasitoids are notorious for consuming their living host from the inside out, rendering the host organism little more than a zombie incubator for its parasitoid master. In many cases they start by consuming the non-essential organs so that the host lives as long as possible, only progressing to the essential organs when they are just about to emerge. Once the parasitoid is finished growing it detaches (if it’s external) or burrows out (if it’s internal) from the host body and continues on its merry way, ready to mate and find a new host for its eggs.
Parasitoid species are many and varied, and they attack many other organisms besides butterflies. Read about a cool parasitoid wasp that targets the Hemiptera, or true bugs here!