Poison hemlock (Conium maculatum, family Apiaceae) is one of the deadliest plants in North America. This non-native invasive weed contains highly toxic piperidine alkaloid compounds, including coniine and gamma-coniceine, which cause respiratory failure and death when ingested by mammals.
It is native to North Africa and Eurasia including Greece and is the plant behind the “hemlock tea” that was responsible for Socrates' famous last words, "I drank what?" Not really; that’s fake news. But, his last words certainly weren’t, “pour a round for the house,” because we do know Socrates’ actual last words thanks to a witness referenced in Plato’s dialogue titled, Phaedo (Phaedo of Elis was one of Socrates’ followers). His final words were: “Crito, we ought to offer a cock to Asclepius. See to it, and don’t forget.”
Really? He ordered a chicken dinner for a friend?? Frankly, when I first learned this, I heard the sound of a deflating balloon in my head. In fact, the exact meaning behind Socrates’ last words has long been debated by scholars … which is why I like my fake news version better.
While photographing poison hemlock plants going to seed last season, I came across a number of plants heavily infested with Fennel Aphids (Hyadaphis foeniculi). Even more startling, Multicolored Asian Lady Beetles (MALB) (Harmonia axyridis) were grazing on the aphids with no apparent ill effects. I visited that same poison hemlock patch today and found that the aphid and MALB populations are even higher. I also observed green lacewing eggs perched on their stalks on the stem of a heavily infested poison hemlock plants.
It is apparent by the small numbers of herbivorous insects that will feed on poison hemlock that insects aren’t necessarily immune to the alkaloid toxins. However, fennel aphids are obviously able to handle the toxins without going the way of Socrates. And, they aren’t the only aphids that can sip poison hemlock sap. Others include: Pear-Parsnip Aphid (Anuraphis subterranean); Milkweed Aphid (Aphis asclepiadis); Foxglove Aphid (Aulacorthum solani); Hawthorn-Parsley Aphid (Dysaphis apiifolia); and Honeysuckle Aphid (Hyadaphis passerinii), just to name a few.
The common names for some of these aphids indicate they have an ability to detoxify some pretty serious plant toxins. Apparently the fennel aphid’s deactivation of the poison hemlock alkaloids is sufficient to make them vulnerable to predators including MALB and green lacewings. However, the aphid populations I observed today were much higher than last season calling into question the overall impact of the lady beetle predation.
Given that the biennial poison hemlock plants are producing seed and are nearing their annual decline and collapse, it would seem the predators may soon lose the plants supporting their bountiful aphid bistro. On the other hand, fennel aphids are capable of feeding on a number of other plants including their namesake host; they can be a serious pest of fennel. Thus, poison hemlock may serve as an early season reservoir for this aphid supporting the rapid development of high populations on other plants in the summer. Of course, it’s also possible the predator/prey dynamic will follow with the MALB-wolves trailing their aphid-sheep to new pastures.
My speculation may not withstand cooperative argumentative dialogue stimulating critical thinking. Perhaps underlying presumptions could be further drawn out over a nice chicken dinner washed down with a few cups of tea.