Thursday, June 20, 2024

A red admiral alights in the Agassiz neighborhood of Cambridge on July 11, 2021. (Photo: Tianzhu Xiong)

Because of the name, you might think the red admiral butterfly (Vanessa atalanta) is somehow associated with the sea or sailors or seafaring. The red admiral butterfly has nothing to do with the ocean. It was originally called red admirable, presumably because it was a butterfly with many qualities to be admired, and that term became shortened to red admiral.

Red admirals are one of the most common butterflies in the state (and in the entire world). You can find them in North and South America, Europe, New Zealand and Asia. In Massachusetts, you can spot them from May to October.

A red admiral in Groton on Sept. 21, 2021. (Photo: Robert Gessing)

One of the reasons red admirals are so common is that the caterpillars eat nettles – all kinds of nettles, but especially stinging ones. Nettles, those jagged-leaved plants with stinging hairs, grow around the world in almost every region, so these butterflies are found around the world in almost every region, too. Nettles grow in the wild, but they are weedy and also grow in urban and disturbed landscapes. For this reason, the red admiral is one of the most common city butterflies.

Adult butterflies do not eat; they only drink. So adult red admirals are attracted to wet things. They wick up water, minerals and electrolytes from sap, rotting fruit, bird droppings, wet soil and the nectar of plants, including milkweeds, goldenrods, asters, meadowsweet, wild bergamot and Joe-Pye weed.

Red admiral caterpillars are dark and spiky with yellowish markings along the sides. (Photo: Teá Montagna)

Red admiral butterflies migrate, so they do not overwinter in Massachusetts like some other butterflies. Each spring, migrants from the south return to recolonize Massachusetts. These migrants fly at high altitudes where high winds help propel them great distances. The population varies from year to year depending on how many butterflies return.

The first red admirals arrive in early May. They mate, and the female lays eggs on nettle plants. Tiny spiny caterpillars emerge from the eggs. They eat nettles and grow and grow. Unlike monarchs, which are toxic to predators, red admirals are a tasty treat. So they camouflage themselves for protection from birds and other predatory creatures: They fold over a leaf to make a shelter that hides them from predators; later, underneath a leaf, each caterpillar hangs upside down and metamorphoses into a hanging chrysalis. The chrysalis looks like a dead leaf.

Red admirals have orange bands on the fore and hind wings. (Photo: Tom Murray)

A second generation of red admirals appears in early July. A third generation appears in late August through October. Some butterflies from this third generation migrate south to southern Texas.

Male red admirals are quite territorial. A red admiral will chase away any other male that enters its oval territory (often about 16 feet long by 24 feet wide). Males fly around the perimeter of their territory up to 30 times per hour. They chase away intruders 10 to 15 times per hour. If you see two red admirals fluttering and looping around each other, they are not playing or dancing. One butterfly is probably chasing the other away, for female red admirals will mate only with male red admirals that can maintain a territory.

A red admiral rests near Tufts University in Somerville on Sept. 1, 2020. (Photo: Jeanine Farley)

Every once in a great while, red admirals migrate in enormous numbers. In 1990, for example, Massachusetts spectators could count hundreds of red admiral migrants per hour. The same thing happened that year around the western shore of the Caspian Sea in Russia.

If you want to attract red admirals, try putting out a plate of fruit, or grow nettles or nectar flowers in your garden. These butterflies also like salt, so if you are sweaty, one might even land on you!

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Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.