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Archive for August, 2012

This, my third post about the Giant Swallowtail butterfly (Papilio cresphontes), will focus on the larvae.

Papilio cresphontes giant swallowtail young larva Dictamnus albus

Larva or bird dropping?

The young larvae are a shiny dark brown with cream-colored patches–they look like warty bird droppings. As they get older, the larvae develop scale-like markings about their heads and look like tiny snakes when viewed from the front. These disguises help to protect the larvae from predators—young larvae appear unpalatable and older ones resemble frightening adversaries. The larvae also can ward off potential predators by thrusting out their osmeterium, a pair of bright red, retractable horn-like structures. In older larvae, the osmeterium emits an unpleasant stench that repels potential invertebrate predators like spiders and ants. The osmeterium’s likeness to a snake’s tongue may frighten larger predators like birds. The Dragonfly Woman has a nice video on her blog of a larva extending its osmeterium.

Eastern Garter Snake Thamnophis sirtalis sirtalis

Older larvae mimic snakes like this Garter Snake

After molting through five stages, the larvae ultimately reach a stout 2 to 2 1/2” (51 to 64 mm) long. They then seek out a nearby vertical stem or other surface on which to pupate. In northeastern North America, the Giant Swallowtail overwinters as a pupa.

In Florida’s warm climate, where Giant Swallowtail butterflies are common, there are two or three generations each year. There, the larvae often feed on citrus trees like sweet orange and are called Orange Dogs. They’re considered pests because they can defoliate young trees.

Update on the larvae in my garden

Papilio cresphontes giant swallowtail larvae eating Dictamnus albus

Bulking up on Gas Plant

In my August 19 post, I wrote that I had found three Giant Swallowtail eggs on the Gas Plant (Dictamnus albus) in my garden, followed by two larvae about a week later. As of today, I’ve counted six larvae scattered on the leaves of the Gas Plant. Five larvae are about the same size—5/8” (16 mm) long. The sixth larva, which I discovered yesterday, is smaller, only about 1/4” (6 mm)  long. I suspect that the small larva may be the offspring of an adult female that visited my garden unseen several days to a week after the adult I saw on August 3.

The larvae often sit on the tops of the Gas Plant leaves, clearly visible bird-dropping imitators. Occasionally, one will appear restless, and will travel back and forth over the leaves for several minutes before settling down again. I’ve read that they feed mostly at night, but I occasionally have seen a larva munching on the Gas Plant leaves during the day. If I touch them with a twig, they arch their backs and thrust out their bright red osmeterium.

Papilio cresphontes giant swallowtail larvae red osmeterium

Red osmeterium deters predators

I’ll continue to monitor the larvae on my Gas Plant and hope to post occasional updates on their development.

Giant Swallowtails moving north  

I first thought the Giant Swallowtail butterfly that visited my garden on August 3 was a rare sight. Since then, I’ve learned that lots of people in my area and farther north have seen Giant Swallowtails this year and that sightings in the north have been increasing for about five years. This northward movement may be due to changing weather patterns, decreased pesticide spraying, or some other as yet unknown reason. Whatever the reason, we northerners have had the treat of seeing these large, beautiful butterflies close to home.

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In my previous post, I wrote about a Giant Swallowtail butterfly that visited my backyard in early August, an unusual sight for my area. I sought to learn more about this butterfly species.

Adult butterflies seek out areas that contain their larval host plants, those specific plant species that females lay their eggs on and that their caterpillar larvae feed on. Per butterfly field guides, various members of the Rue (Rutaceae) family are the host plants of the Giant Swallowtail. The better known members of this family are citrus trees like sweet orange (Citrus × sinensis). That’s why the Giant Swallowtail is so common in Florida. Farther north, native members of the Rue family include Prickly Ash (Zanthoxylum americanum) and Common Hop Tree (Ptelea trifoliata). (more…)

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It’s always exciting to see a new species of plant or animal, especially one that’s considered rare in your area. This happened to me earlier this month, when a Giant Swallowtail butterfly (Papilio cresphontes) visited my northern New Jersey backyard. This large, attractive butterfly is common in Florida, but becomes less abundant farther north.

Giant swallowtail or Papilio cresphontes dorsal

Giant Swallowtail

(more…)

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