Of Spreading Dogbane and Butterflies

Summer time for me is the season for fresh local fruit and ... wildflowers! Since this is a group devoted to the study of our local flora, I am confident that there are others who share my excitement about taking a hike to a new section of the woods in the cool of the morning hours and discovering yet another new wildflower. I get a sense of satisfaction from making a new notation in my Newcomb’s for that new wildflower sighting.

Lately, I have taken on the task of identifying butterflies in our area - great spangled fritillaries, little wood satyrs, orange sulfurs, etc. Unlike wildflowers, the challenge with identifying butterflies is that they just won’t stay still for this curious naturalist, which usually results in a chase. Anyway, wildflowers, especially ones in sunny areas, are generally aflutter with butterflies, each busily probing its host plant with its proboscis, or mouthpart, seeking nectar. So, to fully appreciate our wildflowers, it is prudent to learn who their pollinators are. Butterflies are among the many flying insects that happily take on this job.

One of the host plants which several of our local butterfly species depend upon is Spreading Dogbane, Apocynum androsaemifolium. Here in the Finger Lakes region, it blooms from late June to early August. This common native is a shrubby wildflower which grows to a height of 2-4 feet. It can be locally abundant, growing in colonies, and in sunny, dry areas such as roadsides, sandy areas, old fields and disturbed places. The delicate, light pink blossoms are about ¼", bell-shaped, and form in loose clusters on the ends of branches. The leaves are oval with a rounded point, alternate, entire, hairy beneath, and up to 4" long. Its distinct reddish stems lack a defined central stalk. The fruit are long, slender, and pointed pods, found hanging in pairs. (Ladd, 2001)

Dogbane is an old-fashioned term, referring to the fact that it was once used to treat a dog bite. “The only apparent connection between the American plant and dogs was its occasional use to treat people bitten by mad dogs.” (Sanders, 2003) However, “... they are certainly the bane of flies and various other smaller insects for whom they are a deathtrap.” (Sanders, 2003) Other insects with shorter mouthparts become mercilessly stuck in the flower’s interior area, which is barbed. These unwelcome pollen poachers are hopelessly trapped and die. It is common to see these dead insects dangling by their tongues from the flower. (Sanders, 2003)

Typical of dogbanes, the latex-like sap is poisonous and acts like a deterrent to most animals. It is mildly toxic to humans. When exposed to air, the white sap will dry into a soft rubbery substance. Since the leaves have an intensely acrid taste, this plant was once called bitterroot. (Sanders, 2003)

By design, dogbane flowers are adapted to attract butterflies, upon which the wildflower is dependent as a pollinator. A butterflies, such as a monarch, dips its proboscis into the blossom to collect the sweet nectar therein. The nectar serves as an attractant to lure the butterfly into the pollen-bearing region of the flower. (Sanders, 2003) The pollen brushes off onto the legs and other body parts of the pollinator, which is then transported to neighboring plants of the same species for fertilization, ensuring genetic variety. While this plant maybe poisonous to most mammals, it is highly attractive to butterflies and other insects. Even though school children are taught that milkweed is their only food, spreading dogbane is also the monarch butterfly’s host plant. They will feed on the leaves and make their chrysalises on the undersides of the leaves. [See editor's note, below.] Like monarchs and milkweeds, the toxins found in the latex sap of the dogbane provide a natural chemical defense against predators once it has been ingested by the butterfly larvae. (Sanders, 2003) Other butterflies, such as the Canadian tiger swallowtail, cabbage whites, hairstreaks, fritillaries, checker spots, and red admiral, also feed upon spreading dogbane. (Weber, 2002)

Should a colony of dogbane be located near an open hilltop, one may find numerous butterflies clustered at the top, in a behavior known as ‘hilltopping’. This involves mainly the males, actively cruising the singles scene, who congregate at the highest point of the surrounding landscape looking for a mate. Due to the butterfly’s limited distance vision and the fact that its host plants are naturally widely disbursed, hill tops serve as a singles bar. Since males are very territorial, early arrivals choose the most strategic spots to patrol, which is heartily defended, and chasing away rivals is all part of the action. The chances of successfully finding a mate increase significantly if everyone congregates in one area. A female will take a break from seeking a host plant upon which to lay her eggs long enough to fly uphill and mate. It is found that different species of butterflies dominate a hilltop at different times of the day, perhaps as a way of avoiding the distraction of other types of butterflies also seeking mates. Other insects, such as wasps and bees, also use this 'hilltopping' strategy. (Williams, 2005)

Another courtship behavior, ascending flight, occurs when a female is uninterested in the advances of an amorous male. This uninterested female signals that she is unready to mate by flying upwards; the male pursues. The resulting upward spiraling flight occurs when the male pursues the female, but does not take the hint that she is unready to mate. The same instinctive flight pattern occurs between rival males while defending their territories during intense mating activity. (Williams, 2005)

Butterflies gain needed sodium and other nutrients by eating soil and drinking from muddy puddles. In a behavior known as ‘puddling’, male butterflies will congregate at puddles and form ‘puddle clubs’. “It has been shown ... that the sodium accumulated during puddling is passed on, along with sperm, to a female at mating in a nuptial gift he helps by providing nutrients.” (Williams, 2005) These extra nutrients are used by the female for egg production. “Tiger swallowtails are notorious puddlers.” (Weber, 2002) Other sources of sodium are “carrion, animal excrement, sweat-soaked clothing, campfires, and urinals.” (Williams, 2005) So, while puddle clubs are stag parties for males, they also enable the male to contribute to reproduction in a more passive manner. (Williams, 2005)

Other behaviors include nectaring (when the adults feed on nectar, their primary food) and basking, which is when they warm themselves up by “spread[ing] their wings in sunny sites and act[ing] like small solar panels to collect heat.” (Weber, 2002)

Next time you are out hunting for that elusive wildflower, take the time to see who is fluttering in the neighborhood. Remember, wildflowers do not occur in isolation, but are part of a larger interconnecting ecosystem, in which they form a vital link. Without butterflies, there would be no spreading dogbane, and vice versa.

Sources:

Sanders, J. 2003. The Secrets of Wildflowers. Lyons Press, Guilford, CT
Ladd, D. 2001. North Woods Wildflowers. Falcon Publishing, Helena, MT
Weber, L. 2002. Butterflies of New England. Kollath-Stensaas Publishing, Duluth, MN
Williams, E. 2005. The Nature Handbook. Oxford University Press, NY, NY

 

Editor's note Jan. 2014.  Following up on a reader's question suggests that references to monarchs utilizing Apocynum may be a case of repeated references to an original, erroneous report.  Robert Dirig, Cornell, states the following:

"Here's a quote from a long essay on the Monarch that I wrote a few years ago:

Confined N.Y. females refused to oviposit on Spreading Dogbane (Apocynum androsaemifolium, Apocynaceae), nor would larvae eat it.  Literature reports of this plant as a Monarch larval host may be misidentifications, since dogbanes also contain milky latex and superficially resemble slender milkweeds.

I have never found a wild larva on either Spreading Dogbane or Indian Hemp. Female Monarchs also would not lay eggs on local Vincetoxicum/Cynanchum species, and larvae wouldn't eat them.  In the Northeast, they seem to be confined to milkweed hosts (Asclepias)."