|honeybee on butterfly weed (Asclepias tuberosa)|
|Monarchs visiting in October last year|
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|
|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|
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|
|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.