This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
Flowers - Delicate pink, veined with a deeper shade, fragrant, bell-shaped, about 1/3 in. across, borne in loose terminal cymes. Calyx 5-parted; corolla of 5 spreading, recurved lobes united into a tube; within the tube 5 tiny, triangular appendages alternate with stamens; the arrow-shaped anthers united around the stigma and slightly adhering to it. Stem: 1 to 4 ft. high, with forking, spreading, leafy branches. Leaves: Opposite, entire-edged, broadly oval, narrow at base, paler, and more or less hairy below. Fruit: Two pods about 4 in. long.
Preferred Habitat - Fields, thickets, beside roads, lanes, and walls. Flotuering Season - June - July.
Distribution - Northern part of British Possessions south to Georgia, westward to Nebraska.
Everywhere at the North we come across this interesting, rather shrubby plant, with its pretty but inconspicuous little rose-veined bells suggesting pink lilies-of-the-valley. Now that we have learned to read the faces of flowers, as it were, we instantly suspect by the color, fragrance, pathfinders, and structure that these are artful wilers, intent on gaining ends of their own through their insect admirers. What are they up to?
Let us watch. Bees, flies, moths, and butterflies, especially the latter, hover near. Alighting, the butterfly visitor unrolls his long tongue and inserts it where the five pink veins tell him to, for five nectar-bearing glands stand in a ring around the base of the pistil. Now, as he withdraws his slender tongue through one of the V-shaped cavities that make a circle of traps, he may count himself lucky to escape with no heavier toll imposed than pollen cemented to it. This granular dust he is required to rub off against the stigma of the next flower entered. Some bees, too, have been taken with the dogbane's pollen cemented to their tongues. But suppose a fly call upon this innocent-looking blossom? His short tongue, as well as the butterfly's, is guided into one of the V-shaped cavities after he has sipped; but, getting wedged between the trap's horny teeth, the poor little victim is held a prisoner there until he slowly dies of starvation in sight of plenty. This is the penalty he must pay for trespassing on the butterfly's preserves! The dogbane, which is perfectly adapted to the butterfly, and dependent upon it for help in producing fertile seed, ruthlessly destroys all poachers that are not big or strong enough to jerk away from its vise-like grasp. One often sees small flies and even moths dead and dangling by the tongue from the wicked little charmers. If the flower assimilated their dead bodies as the pitcher plant, for example, does those of its victims, the fly's fate would seem less cruel. To be killed, by slow torture and dangled like a scarecrow simply for pilfering a drop of nectar is surely an execution of justice mediaeval in its severity.
In July the most splendid of our native beetles, the green dandy (Eumolpus auratus) fastens itself to the dogbane's foliage in numbers until often the leaves appear to be studded with these brilliant little jewels. "It is not easy," says William Hamilton Gibson, "to describe its burnished hue, which is either shimmering green, or peacock blue, or purplish-green, or refulgent ruby, according to the position in which it rests." But it is not golden, as its specific name would imply. It confines itself exclusively to the dogbane. To prevent capture, it has a trick of drawing up its legs and rolling off into the grass its body so cleverly matches.
From the silky coma on which the small seeds float away from long pods to found new colonies, from the opposite leaves, milky juice, and certain structural resemblances in the flowers, one might guess this plant belonged to the milkweed tribe. Formerly it was so classed; and although the botanists have now removed its family one step away, the milkweed butterflies, especially the Monarch (Anosia plexippus), ignoring the arbitrary dividing line of man, still includes the dogbane on its visiting list. We know that this plant derived its name from the fact that it was considered poisonous to dogs; and we also know that all the tribe of milkweed butterflies are provided with protective secretions which are distasteful to birds and predaceous insects, enjoying their immunity from attack, it is thought, from the acrid, poisonous character of the foliage on which the caterpillars feed.