Yesterday while tagging in backyard garden at the Point, Lynn (the newest member of the Monarch team) spotted a Viceroy, which was perched on the same patch of blooming ivy where we had observed many Monarchs. I thought this was interesting because not only had the Viceroy obtained protection from predators by copying the Monarch's black and orange coloring, but he was further protected by hanging out with an entire swarm of Monarchs. But this Viceroy was also helping keep the Monarchs safe from predation! How did this work? Monarchs are poisonous to nearly all vertebrate predators due to a collection of heart toxins that the Monarch larvae acquired from their hostplant, milkweed. The Monarchs advertise their toxicity with their brightly colored wings. It only takes one bite of a Monarch to teach birds or other predators to avoid orange and black colored butterflies! And so, a bird who has learned to avoid Monarchs will also avoid Viceroys, who have evolved to copy the appearance of the Monarch to take advantage of that advertised chemical toxicity (Batesian mimicry). At least that is how the story went for many years. Recently, scientists have determined that many Viceroys are poisonous in their own right, especially those whose larvae fed on willows and poplars high in salicylic acid. So it now seems that the Monarch and the Viceroy are both mimicking one another! The Monarch gains more anti-predator protection by looking like a poisonous Viceroy, and Viceroy is protected by looking like a poisonous Monarch (Mullerian mimicry). See the original sources: Experimental studies of mimicry in some North American butterflies: Part I. The monarch, Danaus plexippus, and viceroy, Limenitis archippus archippus & The viceroy butterfly is not a batesian mimic
On the Monarch numbers front, yesterday was a very good day (387 Monarchs/hour). The beginnings of several roosts in the neighborhood around the Point were observed around 4:30 pm. You can now check out the day's Monarchs per hour rate at our website, MMP Data Page, which will be updated by approximately 6 pm EST daily.