The milkweed community

Common milkweed, that singular plant found at the edge of forests or alongside agricultural fields, is the host plant of the majestic monarch butterfly. In mid-July, its magnificent pink flowers give off a pleasing scent. If you crouch down to get a better view of them, you quickly notice the diversity of insects hiding there – and this despite the plant’s toxicity.

A diversified and flamboyant community

Because of its toxicity, milkweed hosts a very special insect community. Those who choose to settle in there have succeeded in overcoming the plant’s defense mechanisms. Monarch butterfly caterpillars come to mind: they devour milkweed leaves at a remarkable rate and store the toxins in their tissues.

Besides the monarch, milkweed plays host to these inhabitants: the milkweed tussock moth, the small milkweed bug, the common milkweed beetle – and other species as well! Some have hairy bodies, while others are plump. But these insects that make milkweed their host plant have one feature in common: they all display flamboyant colors to signal their toxicity.

In search of nectar

Although milkweed tissues are the food source for certain insects, others, those belonging to the hymenoptera order, prefer to drink the plant’s sweet nectar. Bees and bumblebees are frequent visitors. And they’re incidentally responsible for a good deal of this plant’s pollination.¹

Discrete visitors, but effective!

Did you know that milkweed also receives visits from a number of nocturnal insects? Once night falls, a different community of insects gathers around the plant, including moths (primarily Tiger and Lichen moths (Arctiinae),  geometrid and noctuid moths).^1,2 Although less flamboyant, the milkweed’s night time visitors are every bit as important.

According to some scientists,^1,3 nocturnal insects achieve higher-quality pollination. In effect, each little “bag” of the milkweed’s pollen (called a pollinium) removed by a nocturnal visitor will be four times more likely to develop a follicle than if taken by a diurnal insect. However, that difference in pollination quality is largely offset by diurnal visitors’ more numerous visits to the milkweed’s flowers.^1,2 One thing is certain for nocturnal insects: they’ll be rewarded for their visits, because common milkweed produces a sweeter, more abundant nectar at night than during the day¹ – just what it takes to satisfy the most avid appetites!

Invite milkweed into your garden

This spring, why not create a place for milkweed in your garden? It’s amazing to see the range of insects that the plant shelters. And don’t forget that you can report all sightings of monarchs that have found refuge in your milkweeds on the mission-monarch.org site. It’s a concrete and fun way to help this endangered species.

References

1. Howard, A.F., Barrows, E.M. (2014). Self-pollination rate and floral-display size in Asclepias syriaca (Common Milkweed) with regard to floral-visitor taxa. BMC Evol Biol 14, 144, doi: 10.1186/1471-2148-14-144.
2. Jennersten O., Morse D.H. (1991). The Quality of Pollination by Diurnal and Nocturnal Insects Visiting Common Milkweed, Asclepias syriaca. Am. Midl. Nat. 125:18-28.
3. Bertin, R.I., Willson, M.F. (1980). Effectiveness of diurnal and nocturnal pollination of two milkweeds. Can. J. Bot. 58: 1744-1746.