Posts Tagged ‘ecosystem’

The Milkweed Community

May 13, 2015
Monarch butterfly on common milkweed © Beatriz Moisset

Monarch butterfly on common milkweed
© Beatriz Moisset

The monarch season is coming, and many gardeners throughout the country are getting ready to welcome the arriving butterflies with milkweeds lovingly cultivated in their gardens. They also brace themselves to battle whatever ills may affect the caterpillars. Milkweed bugs and milkweed beetles are seen with hostility. The “dreaded” tachinid flies, and “hated” stink bugs infuriate gardeners even more. Aphids are not welcome. Lady beetles and lacewings generate mixed feelings because they feed on aphids but they are not loath to snack on some monarch eggs or small caterpillars.

Spotted Lady Beetle larva (Coleomegilla maculata) © Beatriz Moisset

Spotted Lady Beetle larva (Coleomegilla maculata)
© Beatriz Moisset

It is important to take a look at entire ecosystems, not just single species as Carole says in “Saving the Monarch Butterfly

“The Monarch Butterfly is in deep trouble, and many passionate organizations have been created to save this single species. But a focus on protecting habitat instead of concentrating on a single species will provide lasting benefits for all species of wildlife and the native plant communities that support them, a far more worthy effort to many environmentalists and wildlife gardeners.”

So, let us take a quick look at some members of the milkweed community. Despite the formidable defenses these plants have, many species have coevolved with them and can use them as food. They incorporate the milkweed toxins and use them to deter their enemies. In turn, many predators have also coevolved and can eat the milkweed eaters. An entire food chain has developed this way.

Large milkweed bug, Oncopeltus fasciatus on common milkweed © Beatriz Moisset

Large milkweed bug, Oncopeltus fasciatus on common milkweed
© Beatriz Moisset

Milkweed longhorn beetles on common milkweed © Beatriz Moisset

Milkweed longhorn beetles on common milkweed
© Beatriz Moisset

Most monarch lovers are familiar with the brightly colored milkweed bugs and milkweed longhorn beetles. Bear in mind that these insects are represented by a fairly large number of species. That is, there are more than just one milkweed bug and one milkweed beetle. A few other beetles also feed on milkweeds, and several moths also do so, among them the tussock moth and the delicate cycnia.

Tussock moth caterpillar © Beatriz Moisset

Tussock moth caterpillar
© Beatriz Moisset

Sooner or later, those who raise monarch caterpillars are bound to meet two insects which will make them unhappy; one is a predator, the spined soldier bug, the other a parasite, the tachinid fly, Lespesia.

The spined soldier bug, Podisus maculiventris, is a good hunter of caterpillars and beetle grubs. It has a sharp beak with which it impales its victims. It injects some saliva which turns the inside of the prey into a smoothie and so it proceeds to drink this nutritious cocktail. The sight of a shriveled monarch caterpillar hanging from the beak of a stink bug causes great distress to the gardener.

Predatory stink bug, Podisus maculiventris on goldenrod. © Beatriz Moisset

Predatory stink bug, Podisus maculiventris on goldenrod.
© Beatriz Moisset

Podisus maculiventris juvenile (nymph) feeding on dogbane caterpillar © Beatriz Moisset

Podisus maculiventris juvenile (nymph) feeding on dogbane caterpillar
© Beatriz Moisset

The tachinid fly mentioned above goes by the name of Lespesia. It lays its eggs on caterpillars of a large number of species. The tiny fly larva digs inside and proceeds to eat its victim until it reaches full size. Then it comes out of the dying caterpillar and dribbles a sticky trail until it drops to the ground. Not a pretty sight.

Tachinid fly, Lespesia © Stephen Luk

Tachinid fly, Lespesia
© Stephen Luk

Tachind fly, Lespesia, Puparium and parasitized tent caterpillar's cocoon © Stephen Luk

Lespesia puparium and parasitized tent caterpillar’s cocoon
© Stephen Luk

Although these two insects on occasion kill some monarchs, we should not hate them. Actually, their diet is so diverse that it includes a number of pests. They are both used as pest controls for this reason and even sold for this purpose. Podisus is known to eat Mexican bean beetles, European corn borers, diamondback moths, corn earworms, beet armyworms, fall armyworms, cabbage loopers, imported cabbage worms, Colorado potato beetles, and velvetbean caterpillars. The tachinid fly is reported to feed on tent caterpillars, armyworms, cutworms and corn earworms.

Nature is far more complicated than it appears at first sight. It may seem paradoxical, but the spined soldier beetle and the Lespesia fly are indirectly the friends of monarchs, because they help cut down on pesticides. Moreover, we must remember that they have coexisted with monarchs for eons without driving them to extinction. The same can be said about the milkweed herbivores –beetles, bugs and moths. They haven’t driven milkweeds to extinction and they are not likely to do so. We are the ones that pose a threat to milkweeds and to monarch butterflies with our pesticides, habitat destruction and introduction of invasive species.

Let saving the pretty butterfly be the portal to saving the entire community, all the creatures that creep and crawl, the ones that jump or fly and even the ones that kill or get killed. Let us embrace the web of life in its totality, with all its beauty and ugliness.

Delicate cycnia © Beatriz Moisset

Delicate cycnia
© Beatriz Moisset

Additional readings
You may find this Flickr album interesting: Milkweed Visitors
More members of the milkweed community
The monarch butterfly as part of the food web: Monarchs and their Enemies

This article first appeared in Native Plants and Wildlife Gardens


Introduced species, discordant notes

July 18, 2010

I would like to recommend three books that illustrate the impact of the ever increasing numbers of human introduced species into habitats not their own; they analyze the effects of some of these introductions, describe measures used to control or prevent the consequences of such introductions, and make suggestions about what you can do.

+ Nature Out of Place: Biological Invasions In The Global Age by Jason Van Driesche and Roy Van Driesche, 2004
+ A Plague of Rats and Rubbervines by Yvonne Baskin. 2003
+ Bringing Nature Home: How You Can Sustain Wildlife with Native Plants by Douglas W. Tallamy and Rick Darke. 2007

These books show us that ecosystems are like symphonies. It takes millions of years of co-evolution to develop a fine tuned system, richly complex and delicately balanced. If you took a well crafted symphony and added a snippet of music from another composition, the introduction wouldn’t fit with the rest of the work. The composer could weave this introduction into the symphony by tweaking the alien fragment and the related parts until it all worked well together once again. It would take some time and effort but it can be done. However if a large number of musical fragments are introduced it becomes impossible to repair the piece. Likewise ecosystems have been dealing with introduced species all along; it may take many thousands of years, perhaps millions, but eventually the non-native species become part of the ecosystem. Unfortunately, in recent times, humans have been moving species around, intentionally and unintentionally, at unprecedented rates. The numbers of species invading new environments far exceed the pace of evolution; ecosystems suffer serious disruptions as a consequence.

Tallamy’s book, in particular, had a profound effect on me. I wish I could summarize its main premise in just one sentence; I will try: most land birds (and many other creatures) need insects and, in turn, insects need native plants in the immense majority of cases. In other words, introduced plants provide no food for native insects and as a consequence birds go hungry.
He presents abundant proof of this thesis, for instance, in one study done in Oxford, Pennsylvania “native plants supported 30 times more caterpillar biomass than alien plants supported.” Other work shows that the Asian reed Phragmites australis sustains 170 species of herbivores in its native land while it feeds only 5 species in North America. More than 300 years have passed since its introduction and it is still no good at sustaining native herbivores.
I can assure you that, if you are a gardener and a bird lover, you will never grow a non-native plant again after reading this book.