The Web of Life: July 2013

Monarch butterfly, adult female. It nectars on a variety of flowers

Monarch caterpillar, It feeds only on milkweeds

Monarch butterflies capture our hearts with their beauty and intrepid globe trotting. We have learned that the caterpillars need milkweeds to grow into the magnificent winged creatures. As a consequence, many gardeners gladly grow these plants in their yards and welcome the arrival of the travelers. They eagerly follow the appearance of the tiny caterpillars, their growth and final metamorphosis.

This leads many to learn more about these plants, their toxicity and the other visitors attracted by the overpowering sweet aroma of the flowers. Some gardeners don’t see them as weeds anymore but as nice additions to their butterfly gardens. Did you know that there are more than 100 species of milkweeds or Asclepias in North America? Did you know that monarchs are not the only ones that depend on milkweeds? Many other insects do. The whole story is infinitely more complex than just milkweed plant/monarch butterfly. A patch of milkweed plants is a community with many herbivores taking advantage of it, followed by carnivores, not to mention numerous pollinators.

Some of the members of this community depend exclusively on milkweeds while others benefit from these plants, but have other food choices. Pollinators and predators, fall in the second category.

Let us take a look at those that are dependent on milkweeds, those which need these plants to complete their development from egg, through immature or larval stages to adulthood. Some eat leaves; others go for stems, roots or seeds. Their tastes can be highly selective, feeding on only one or at most two species of milkweeds. Others, like the monarch butterfly, have broader tastes and accept most species of milkweeds or even some related plants. It is the growing insects that are dependent. The adults, in turn, may not need milkweeds, but they frequent these plants to lay their eggs on them.

Milkweeds have developed an assortment of defenses, such as sticky latex, hairy leaves and powerful toxins, against the cadre of hungry feeders. The eaters, in turn, have gradually found ways to overcome every one of these barriers. Milkweeds respond by producing more latex, hairier leaves, and stronger toxins. In this eternal arms race nobody wins, but nobody loses either. Like a carefully choreographed ballet, the equally matched enemies continue this dance of life and death affecting each other and in turn influencing the other members of the community.

Delicate cycnia (Cycnia tenera)

Its caterpillars feed on milkweeds

The best known, of course, is the monarch butterfly. Let us not forget its close relatives, the queen and the soldier butterflies. It is worth mentioning that a few other relatives live in South America and Africa. They are all fairly flexible and can resort to more than one species of milkweed.

Milkweed tussock moth caterpillar
feeding on common milkweed

Among the moths dependent on milkweed, the delicate cycnia (Cycnia tenera), with a very appropriate name, relies only on common milkweed and swamp milkweed. The milkweed tussock moth (Euchaetes egle) has broader tastes and can live on several species of milkweed.

Red milkweed beetle (Tetraopes tetrophthalmus)
feeds on common milkweed

Moving on to other dependents we find beetles. We are most familiar with the milkweed longhorned beetle, often found on common milkweed. If we translate the scientific name of the most familiar one, Tetraopes tetrophthalmus, we would call it the four-eyed four-eyes, although it is known as the red milkweed beetle. The peculiar eyes of all the Tetraopes beetles are divided by the base of the antennae, hence the name. But it gets more complicated because instead of just one species there are at least 14 related and similarly looking species of four-eyed milkweed beetles. Each species sticks to only one or at most two species of milkweed. For instance, the red milkweed beetle feeds only on common milkweed, the red-femured milkweed borer on showy milkweed, and the blackened milkweed beetle on swamp milkweed.

The list goes on and on. It includes beetles of several families. For the sake of briefness see images of a few of them.

Swamp milkweed beetle larva (Labidomera clivicolis)
feeding on milkweed

Dogbane beetle. Larva feeds on dogbane or milkweed

Milkweed stem weevil (Rhyssomatus lineaticollis)

Larvae of several species feed on milkweeds

Small milkweed bug (Ligaeus kalmii)

Large milkweed bugs (Oncopeltus fasciatus)

Let us take a look at the milkweed bugs. The most familiar ones are the large milkweed bug (Oncopeltus fasciatus) and the small milkweed bug (Lygaeus kalmii). Curiously, despite their names, they are not entirely dependent on milkweed. They have been seen feeding on other plants, and even on other insects, in the case of the small milkweed bug.

Milkweed aphid (Myzocallis asclepiadis)

feeding on common milkweed

Several kinds of aphids attack milkweeds. Two of them are dependent on common milkweed. They are Aphis asclepiadis, and Myzocallis asclepiadis; no common name for these either.

All these and many more feed on milkweeds, some on only one species, others on several or many.

When we nurture monarch butterflies by planting milkweeds we are doing more than aiding the butterflies. We are helping the entire milkweed community or series of communities. The members of such communities or ecosystems interact with each other and, in turn, with a wide arrangement of other participants of this intricate play, such as neighboring plants and soil organisms. By preserving the habitat of monarchs, we are also preserving biodiversity. All species are important and we need to respect these communities and learn more about them.