Thirteen years ago I went and sat in a field full of Common Milkweed (Asclepias syriaca). The photographs I took of insects visiting the fragrant blossoms ended up being the subject of my first children’s book, Milkweed Visitors. The number and diversity of invertebrates in that patch of milkweed was astounding. Over a decade later I find milkweed flowers alarmingly free of insect visitors. I first noticed this several years ago, and unfortunately the trend has continued. An occasional honey bee or bumblebee, perhaps a swallowtail butterfly or a red milkweed beetle or two can be seen, but nowhere near the number or variety of insects that you found just a few years ago.
Recent studies show that insect populations are declining dramatically not only in milkweed patches, and not only in North America, but in many parts of the world. A global index for invertebrate abundance showed a 45 percent decline over the last four decades. (Yale School of Forestry and Environmental Studies). Researchers say various factors, from the rampant use of pesticides (in particular, neonicotinoids), the spread of monoculture crops such as corn and soybeans, urbanization, and habitat destruction contribute to this decline.
This phenomenon affects everything from pollination to the documented decline in bird populations that feed on flying insects. However, thus far, only the decline of honey bee populations has received widespread public attention, in large measure because of their vital role in pollinating food crops. The rest of the insect world has been widely ignored. Insects play a major role not only in pollination but as predators of insect pests and as food for birds, amphibians and bats. Who knows how many plant species live in symbiotic relationships with highly specialized insects.
Given the importance of insects for agriculture, biodiversity and the health of ecosystems, one hopes that studies regarding the decline of insects will increase in the near future. We can all contribute to a greater understanding of what is happening by participating in “citizen science” projects which undertake monitoring of specific insect species. A list of such projects and how to get involved can be found at https://xerces.org/citizen-science/.
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Milkweed, a perennial plant that can adapt to adverse soil conditions, has recently been recognized as a viable source of fiber for fill for jackets and comforters. Winter coats insulated with a compressed layer of milkweed fluff are have been shown to be as effective at retaining body heat as those filled with down or polyester, and a Canadian company is now manufacturing and selling them.
Although historically considered a “weed,” milkweed came into its own during World War II, when overseas supplies of the insulating fiber from the kapok tree were cut off and milkweed fluff was harvested for use in life jackets. The U.S. government launched a program that enlisted the help of children: if they could fill up a large onion bag of milkweed fluff, they would receive fifteen cents. This incentive proved very popular, and the U.S. was able to stuff over 1.2 million life vests with milkweed fluff. However, after the war, the rising use of synthetics lessened interest in all natural fibers, and milkweed went back to being considered a less than desirable weed.
Recently milkweed populations have been declining, in part due to herbicides and loss of habitat. However, with the growing interest in this plant as a source of commercial fiber it is now being planted as an agricultural crop, with some Vermont and Canadian farmers devoting acres of farmland to its growth. This, of course, is a boon to monarchs, as milkweed leaves are the sole source of food for monarch larvae. Not only is milkweed being cultivated, but the farmers growing it are making an effort not to harvest the plants until monarchs have migrated in the fall. A win-win situation for all concerned.
Congratulations to those of you who guessed correctly, and thank you to everyone who participated in this week’s Mystery Photo. I find patterns in nature both intriguing and beautiful — they will be the subject of more Mystery Photos! When photographing these Common Milkweed (Asclepias syriaca) seeds, I discovered that there were other creatures attracted to them besides myself – hence, today’s blog post:
LARGE MILKWEED BUGS SIPHONING MILKWEED SEEDS
Only two to four percent of Common Milkweed flowers eventually produce mature pods. Each pod contains an average of 226 seeds (all from one flower). Resembling overlapping fish scales, the seeds are arranged in a way that allows the wind to successively, from the top to the bottom of the pod, catch their silk parachutes and disperse them.
Just as milkweed pods are opening and seeds are maturing, Large Milkweed Bugs (Oncopeltus fasciatus) in all stages of metamorphosis (there are five nymphal stages, or instars) congregate on milkweed pods to feed on the seeds. (Their eggs are laid on milkweed plants.) Like all true bugs, their mouthparts (rostrum) are not adapted for biting and chewing food, but are designed for piercing and sucking. The rostrum consists of two side-by-side tubes. The milkweed bugs use one tube to pump digestive enzymes into the tough milkweed seeds and the other to siphon up the softened plant material. Like other milkweed feeders, milkweed bugs obtain poisonous compounds from the milkweed plant that are used for defense, and their orange and black coloration warns predators of their toxicity.
If you would like to order milkweed seeds, you can find several options at http://www.xerces.org/milkweed-seed-finder/
The Clymene Moth, Haploa clymene, is noted for the striking upside-down cross pattern on its forewings. Because of this design, some people refer to it as the “Crusader Moth.” A member of the Tiger Moth family (as is the Woolly Bear/Isabella Tiger Moth), the Clymene Moth can be seen flying day or night. Typically they inhabit deciduous forests and fields adjacent to them where the black, bristly larvae feed on a wide variety of plants, including willows, oaks, and members of the Aster family. In contrast to its white forewings, the Clymene Moth’s hind pair of wings is bright yellow. Its long proboscis allows it to reach deep inside the nectar-bearing hoods of Common Milkweed.
According to the Vermont Center for Ecostudies, this spring and summer there’s been an estimated drop of 90% in the overall monarch population in eastern Canada – the most dramatic decline ever recorded. Vermont (and most likely New England in general) is experiencing much the same situation. The low numbers of monarchs are due to several factors that they have encountered along their migratory routes the past couple of years, including extreme temperatures, record drought, low nectar production by flowering plants and a scarcity of their host plant, milkweed. The cold temperatures and record amounts of rain this spring undoubtedly added to their stress.
Of all the insects I’ve found in milkweed patches over the years, the Hummingbird Clearwing is one of my favorites. It is a species of sphinx moth, named for its habit of hovering at flowers while it gathers nectar with its proboscis in a manner similar to that of hummingbirds. In fact, they are often mistaken for hummingbirds. The transparent wings, light brown thorax and dark chestnut abdomen are the field marks to look for. A diurnal moth, the Hummingbird Clearwing can often be found during the day in milkweed patches.
Milkweed is in full bloom right now, presenting the perfect opportunity for young and old alike to discover the multitude of butterflies, beetles, bees and other insects that are attracted to these magnificent flowers. If you visit a milkweed patch, don’t leave before getting a good whiff of the flowers’ scent – one of the sweetest on earth. How many of the insects you find are carrying milkweed’s yellow pollen “saddlebags” on their feet? You might want to check out my children’s book, MILKWEED VISITORS, which I wrote after spending the better part of one summer photographing the various insects I found visiting a milkweed patch. ( http://basrelief.org/Pages/MV.html )
This time of year you can often find many orange and black bugs on milkweed leaves. If they are black with an orange “X” on their forewings, they are small milkweed bugs (Lygaeus kalmii). This combination of colors, which many insects that feed on milkweed have, warns predators that, due to ingesting milkweed toxins, red and orange insects may be bad for their health. Adult small milkweed bugs feed mainly on milkweed seeds, but they also consume the nectar of a variety of flowers. In addition, they occasionally prey on insects, such as the ant in the accompanying photograph.
We think of monarch larvae as being impervious to the ills of milkweed, but they are very vulnerable when it comes to the sticky latex in the sap of their host plant. The mandibles of young monarch caterpillars are often glued together by this latex, preventing them from eating. Research shows that about 30 percent of monarch larval loss results from miring in this glue-like substance. One strategy young larvae use is to chew a near circle in a milkweed leaf, blocking the flow of latex to the enclosed surface area, which they then eat. If a monarch survives the first few stages, or instars, of its larval life, it uses yet another strategy to circumvent the latex. Older, larger larvae often cut through the midvein of a leaf they wish to consume, which dams the latex flow to the entire leaf beyond the cut. Look for limp leaves as you peruse a milkweed patch. If you find one, you may be rewarded with the nearby presence of a monarch caterpillar.