Creating a wildlife haven one plant at a time

Sunday, August 23, 2015

Got Milkweed?

Then you have an ecosystem.  Usually we think of ecosystems as big areas like a forest, meadow or lake. But a single plant can play an important role in the survival of a single species or several species.

honeybee on butterfly weed (Asclepias tuberosa)

Most gardeners plant milkweed (Asclepias) to support monarch butterflies. The precipitous decline in their population is reason alone to be planting all the milkweed we can in our gardens as milkweed habitats across the country are dwindling quickly. Every year I plant more milkweed in the hopes that monarchs will come. But they don't always show up. Last year, I mourned the absence of these spectacular butterflies as none were seen in our garden during either their spring or fall migration. In previous years we've had up to 12 arrive at the same time, usually in fall when the winds favorably blow our way. Sadly, we haven't had any monarch caterpillars here since spring 2011.

Monarchs visiting in October last year

(For a list of native milkweed species that grow in Georgia here is a field guide)

Monarch butterflies may not be the most abundant insects found on milkweed but they are certainly the most familiar.  There are other insects, who are also dependent on milkweed plants and couldn't survive without it, while some insects simply use milkweed as a major food source.

Eastern Tiger Swallowtails on Asclepias tuberosa

Milkweed blooms provide nectar for an array of pollinators including butterflies [such as the Tiger Swallowtail, Painted Lady, Great Spangled Fritilary, Buckeye, Black Swallowtail, Pipevine Swallowtail, Pearl Crescent, Clouded Sulphur], honeybees, wasps, and bumblebees.

But, did you know that milkweed is also a vital host plant for several other insects?

There is another caterpillar, usually found in late summer, that eats the older leaves of milkweed and unlike the monarch caterpillars who prefer young, vigorously growing shoots, this caterpillar will even eat the leaves that are turning yellow and crispy. The milkweed tussock moth (Euchaetes egle) caterpillars are orange, black and white and are nothing but hair. Just check out those long black lashes!

milkweed tussock moth caterpillars
These tussock moth cats are communal feeders who hang out in groups of 10 or more on the leaves. Plants are often blanketed with more than 50 caterpillars. Should you be alarmed seeing so many caterpillars defoliating your plants? I say no. These caterpillars hatch in late summer and are not really competing with monarch caterpillars in my garden, who would hatch in spring or early summer during their northward migration. Any monarchs visiting our garden during the fall will most likely be one of the super generation monarchs and not be laying eggs at this time.

Milkweed Tussock Moth (Euchaetes egle) caterpillars on butterfly milkweed

If you look closely at the stems and tops of milkweed you will probably find little yellow round things. These are not eggs but milkweed aphids, also known as Oleander aphids (Aphis nerii), which were introduced from the Mediterranean region where Oleander is its native host.

milkweed aphids (Aphis nerii) on butterfly weed

Like other aphids, milkweed aphids, tend to have a negative reputation, mostly because they feed by sucking the phloem of the plant, which can sometimes cause damage when in large numbers. I recently learned that scientists have failed to find any male milkweed aphids and therefore believe all the adult aphids are female. They produce without mating, a process called parthenogenesis, from the Greek meaning "virgin creation". The females don't lay eggs but deposit nymphs that are clones of the adult females. When conditions get too crowded on a single plant some nymphs are created with wings so they can fly off to establish new colonies on other milkweed (host) plants.

milkweed aphids, some with wings

Teeny tiny ants are often seen running around furiously on the foliage and pods of our milkweed. This is because the aphids secrete large amounts of watery honeydew attracting ants to the milkweed.

ants searching for honeydew on milkweed

Like other insects that feed on milkweed, the aphids are toxic to most predators because they ingest the toxic cardiac glycosides from the milkweed plant. Their yellow coloring is a warning to predators not to eat them.

Syrphid fly larvae eating milkweed aphids
But there are several predators and parasites that can tolerate the glycosides and help keep the aphid populations in check. Milkweed aphids are food for lady beetles, especially in their larva stage who devour large numbers of aphids daily.

Syrphid fly (aka Flower Flies or Hover Flies) larvae are insect predators too and crawl all over the milkweed foliage eating dozens of aphids each day. And there are tiny aphid wasps (Trioxys, Diaeretiella, Lysiphlebus and Aphidius) that will lay eggs inside the aphids and when the wasp's larva hatch it feeds on the insides of the aphid. Aphids killed in this way are often referred to as "aphid mummies".

There are two types of Milkweed bugs, Large Milkweed bugs (LMB)  and Small Milkweed bugs (SMB), that are found in large numbers on milkweed. The Large Milkweed Bug (Oncopeltus fasciatus) is the most abundant in our garden with many stages present on the plant at the same time.

Large Milkweed bug with nymphs
Milkweed bugs are a true bug so you can call them "bugs" without being frowned upon by your entomologist friends. These bugs go through a simple metamorphosis (vs. complete metamorphosis of butterflies). They lay eggs in the crevices between the seed pods. Females lay around 30 eggs a day or 2,000 in a lifetime. A lifetime being about one month! Just like caterpillars, the milkweed bug nymphs grow through a series of molts, usually 5 instars which are a week long.

Large Milkweed Bug instar beginning to show markings

These bugs have a long proboscis which they use to pierce the seed pods to feed on the seeds. My experience is that they rarely reach the inner seeds and therefore there are still viable seeds for producing more plants. Keep in mind that milkweed plants also spread through rhizomes and will form healthy colonies.

Large Milkweed Bug piercing milkweed seed pod

LMBs also suck sap from the plant so they too are toxic to predators. The bugs are gregarious and in large numbers intimidating to predators. An inexperienced bird may try to eat them but will soon learn that orange and black are warning colors.

Some adults may also feed on nectar and I do notice them occasionally on blooms using their long proboscis like a butterfly.

Large Milkweed Bug on fennel blooms

So, you may be wondering what role these bright bugs play. Well, back in the day, before humans started destroying milkweed habitats, these insects would help regulate populations of milkweed.

Single-handedly, milkweed plants support a group of insects, who are dependent on this plant. Perhaps not all these insects are desirable to every gardener, but my experience is that mature milkweed plants come back each spring with vigor. Our view on insect-plant relationships is often skewed by a few insect "pests" on a relatively small number of crop plants. My approach in our garden is to let nature do its thing, thus creating the biodiversity in the garden that is essential to make it grow productively and keep the balance between plants and insects healthy. And you can enjoy watching life on your own little milkweed ecosystem.

Sunday, August 16, 2015

Swallowtail Madness

Simply spectacular, swallowtail butterflies have a certain allure. Perhaps it's because they are such large butterflies which naturally demand your attention. Maybe it is their elegant tails that gracefully trail their expansive wings as they gently float by. Or simply that their movements flow so easily and look effortless. Whatever the reason they are here to be noticed.

Count them...5 swallowtails on joe-pye weed
Swallowtails adorn blooms in our garden from spring through autumn but the height of summer is when they are most plentiful. In fact, they are everywhere. They are constantly taking my breath away when I see them, especially en masse. I often look out the window and count twenty or more swallowtails covering the Joe-pye weed plants. Watching them flit and flutter through flowers is like watching a ballet where the whole garden is their stage.

They are often seen gracefully emerging from the woods, which is home to many of the host plants for the swallowtail species found in Georgia. They are in search of high energy nectar and they have come to the right place.

Joe-pye weed, butterfly milkweed, monarda, verbena, ironweed and swamp hibiscus are blooming right now and they are magnets for swallowtails. Earlier in the summer buttonbush and devils walking stick were calling to them (read more on Not All Plants Are Created Equally).

Spicebush Swallowtail on Swamp Hibiscus

Spicebush Swallowtail on Swamp Hibisucs

Eastern Tiger Swallowtails (Papillo glaucus) are one of the most recognizable butterflies. Not surprisingly since it is the state butterfly for 5 states (Delaware, Georgia, North Carolina, South Carolina, Virginia) but also because of their unmistakeably eye-catching yellow wings. But can you identify the male from the female?

The female is the showier of the two with her shimmery blue tones on her hind wings.

Eastern Tiger Swallowtail (female)
The male is unquestionably handsome in his own right. Without the distraction of the striking blue chevrons the tiger stripes that give this butterfly its name really stand out.

But the female is tricky because there is another form. She also comes in black which is a mimic of the Pipevine Swallowtail (Battus philenor). This dark morph is often found in areas where Pipevine Swallowtails are abundant. The pipevine plant contains aristolochic acid, which is toxic to some animals making the pipevine caterpillar and butterfly distasteful and hence a butterfly to mimic.

Eastern Tiger Swallowtail (female, dark morph)

Eastern Tiger Swallowtail (female, yellow)
To make things even more confusing, this female tiger swallowtail was spotted in our garden which looks like a blend of the dark and yellow forms.
Eastern Tiger Swallowtail, female (dark & yellow form combo)

Spicebush swallowtail (Papilio troilus) has been another predominant swallowtail in our garden this year. This woodland loving butterfly is a sensation. The hazy aqua green on the hind wings of the male is incredible.

spicebush swallowtail on butterfly milkweed

The undersides of the wing look very similar to other black swallowtails with two bands of orange spots. The differentiating marking is the third spot which is replaced with a blue dash.

Spicebush Swallowtail (third spot is replaced with blue dash)

Eastern Tiger Swallowtail (dark morph)

Despite the tell-tail signs I still sometimes struggle differentiating the dark swallowtails from one another, especially if I don't have a chance to inspect the underside. Is it a female tiger swallowtail in her dark form, male or female spicebush swallowtail? You give it a try.

The spicebush swallowtail will lay its eggs on Spicebush (Lindera benzoin) or Sassafrass (Sassafras albidum). We have both, and this season is the first time we've seen the caterpillars.

In the early instar stages the caterpillar looks like bird droppings sitting on a leaf. By the third or fourth instar the caterpillars are too big to pass as poop so they curl themselves up in the leaves to protect themselves against insectivorous birds and other predatory insects during the day. At night, the caterpillars emerge from the leaves to feed. Wrens are known to bite through the center of a folded spicebush leaf to eat the caterpillar, but if a predator were to see the caterpillar they would think twice before attacking this snake mimic.

In previous years we have enjoyed watching Black Swallowtails (Papilio polyxenes), Pipevine Swallowtails (Battus philenor) as well as Zebra Swallowtails (Eurytides marcellus) find refuge in our garden. This year those swallowtail species haven't been as common as the Tiger and Spicebush Swallowtails. Some years just seem to be more friendly to a certain specie(s) of butterflies than others.

So as we patiently wait for the monarch butterflies to find their way to our garden during their fall migration we will continue to be mesmerized by the allure of these beauties.

Swallowtail butterflies on butterfly milkweed