If you’ve ever picked any part of milkweed, you couldn’t help noticing the deluge of copious white latex spewing forth. If any of the white sticky substance made contact with your skin, its gluey texture and tenacity was soon evident. Milkweeds latex deters herbivory through chemical and mechanical means. Imagine being a little monarch caterpillar freshly hatched from the egg, and your precious tiny mouthparts take their first bite of the world. Whoosh! White toxic glue inundates your mouth and you can hardly muster up the strength to open it again, let alone brave the tidal latex.
But wait you say, monarch caterpillars feed exclusively on milkweed plants, and have evolved various countermeasures to its toxicity and texture. True, yet many individuals perish due to immobilized mandibles and poisoning from especially toxic milkweed individuals. Up to 30 percent of natural monarch fatalities may be due to are older, they will bite the main vein, or midrib, of the leaf in several places to bleed mandibular miring. When the larvaeout the latex and then dine on the distal regions, which are cut off from the latex. Several other milkweed-eating insects have developed similar strategies.
Just like your mama feeding you flax oil by the spoon-full, if it doesn’t kill you, it will make you stronger. The caterpillars that do survive are able to concentrate the cardiac glycoside toxins in their tissues, thus rendering them poisonous and unpalatable to predators. The monarch larvae and butterfly, like most obligate milkweed feeders, are brightly colored to warn of their toxicity.
Pictured here is another common inhabitant of the milkweed patch, the large milkweed bug, Oncopeltus fasciatus. These insects also concentrate the cardiac glycosides in their tissues, and advertise their toxicity with bright red and black coloration. The large milkweed bug feeds gregariously on the immature milkweed seeds while they are still in the pods. With their sucking mouthparts, they inject enzymes into the developing seeds, which liquefies and predigests the contents until it is ready to slurp up. Interestingly, this species is so easy to rear in the lab, that it is the insect equivalent to the lab rat, with countless experiments being performed throughout the land. Some conspiracy theorists believe your next-door neighbors are experimenting on them in their basements.
Notice the yellow do-dads hanging off the feet of these lovebird milkweed bugs. These are masses of pollen, called pollinia. Pollinia are produced in lieu of loose pollen in certain plant families, such as the Orchid (Orchidaceae) and Apocynaceae (Dogbane and Milkweed family). These plants put all their eggs in one basket, by massing copious amounts of pollen in one masse, the pollinium.