Monthly Archives: July 2018

Caterpillars are Taking off Their Skeletons at Hidden Oaks!

DSC_0268The race is on to see who will become a butterfly or moth first. There are Monarchs, Pipevine Swallowtail, and Tobacco Hornworm caterpillars at Hidden Oaks Nature Center in Annandale.

If you happen to visit at the right time, you may see the Monarchs and Pipevine Swallowtail butterflies being released. The Tobacco Hornworm moths will be kept at the nature center to exhibit as adults.


A natural wonder that typically enjoys great favor with humans, the monarch butterfly makes headlines across North America. As an ambassador insect, or one that represents a genre such as pollinators, these insects often are used to teach about life cycles. Ask any second grader, and she will tell you about the struggles of this tenacious insect that depends on one plant, milkweed, for survival.

As wild milkweed decreases, national organizations and neighborhood nature centers encourage people to plant milkweed varieties to support monarchs and other pollinators. With their widespread popularity, it’s no surprise children delight in observing monarch caterpillars being raised at Hidden Oaks.

monarch cat.-aHidden Oaks has championed monarch butterfly awareness and stewardship since 1996. Monarchs usually do not arrive in the Washington area before July, and this year the first batch arrived at the nature center on July 9. Journey North, an online science education project, records the first spotting of monarch eggs throughout the country. Normally, the D.C. area spots monarch eggs on milkweed after June 20. Recently, the date has been creeping earlier on the calendar, with this year’s mid-April sighting the earliest on record. The earlier arrivals may be due to warmer weather and a reduction of milkweed in wintering habitats.

Monarch 2017-aOften the monarchs winging their way through the D.C. area are the last of four generations produced over a calendar year. The last generation is physiologically different from the previous three. The last generation does not typically have the benefit of fresh milkweed and is generally in a nonproductive mode until after their diapause, or overwintering, in Mexico. The previous three generations, which can mate within a week of emerging from their chrysalids, have a life span of about six weeks. The fourth generation, which can live six to eight months, mates after spending months resting – with millions of other monarchs – in the Transvolcanic Mountain range about 60 miles northwest of Mexico City.

More about monarchs

Pipevine Swallowtail

The pipevine swallowtail begins life as a small, black and red caterpillar. This caterpillar has a strict diet, but is a little more flexible than the monarch. It feeds on many varieties of plants in the Aristolochiaceae family, commonly known as the pipevine family of plants. Aside from being delicious for the caterpillar, these plants also contain a toxin that is harmful to many animals, but the pipevine swallowtail is an exception. The caterpillars use this to their advantage and incorporate the toxin into their body where it becomes a defense against predators.

The toxin stays in the caterpillars’ bodies as they go through metamorphosis and turn into butterflies. When the butterflies are old enough to lay eggs, they choose the pipevine plant as their landing pad. This provides some protection to the eggs and ensures that they have something to eat the moment they hatch. Once they hatch, the young larvae remain together and feed as a group. This defense strategy confuses predators, since a group of caterpillars may look like too big of a bite. Once they are older and their bodies possess warning signs of bright orange spikes, they split from the group and feed alone. Pipevine swallowtails are found from the northeastern United States south and west to New Mexico and Arizona as well as in parts of California.

More about swallowtails

Tobacco Hornworm

Hornworms at WRTobacco Hornworm caterpillars are rather striking in appearance, starting out almost translucent, turning bright aqua blue, and then altering to a bright green with white stripes. The caterpillar also has a red “horn” at the posterior end. The caterpillars grow rapidly, starting at around a half-inch and growing to about three and a-quarter inches.

They grow this big because they voraciously munch on tomato plants, much to the dismay of farmers and gardeners. Although tomatoes are their preferred food, they will eat anything in the family Solanaceae, which includes tobacco, pepper, eggplant, and various ornamentals and weeds. The tobacco hornworms at Hidden Oaks have munched through many of the tomato plants, sometimes in as little as a day. After they’ve eaten their fill, they are ready to become moths.

hornwormsWhile the monarch butterfly hangs from a leaf or branch to create its chrysalis, the tobacco hornworm moth forms a pupal cell below the leaf litter or just under the top layer of soil. It is a dark reddish-brown, with a maxillary loop at the anterior (front) end and a pointed posterior (rear) end. Sometimes these pupae can spend an entire winter underground, with the moth emerging in the spring.

Once they have gone through metamorphosis, the adult moth emerges. The wings are mottled black, brown, and white, and fold under in a triangular manner to help provide camouflage. The hornworm is sometimes called a hummingbird moth due to its tendency to fly nimbly among flowers and hover over them to extract nectar with their proboscis.

More about tobacco hornworm

Visit Hidden Oaks to pick up a free packet of native swamp milkweed seeds to attract butterflies and other pollinators to your backyard or school. Share the joy and wonder with your family and friends by experiencing first-hand the variety of native butterflies, and marvel at the mysteries of caterpillars that scientists have yet to completely unravel.

Author Fiona Davies is the Volunteer Coordinator at Hidden Oaks Nature Center.

Sources: University of Florida, Grow Garden Tomatoes, Butterflies and Moths of North America, and GotScience Magazine.