• jjvanm

It’s an unusual time for caterpillars

Published January 1, 2022 in the McAllen Monitor


Story and photos by Anita Westervelt, Texas Master Naturalist, South Texas Border Chapter


As we jump into the new year and approach the coldest months of our Valley winters, I’m seeing some unusual activity – caterpillars – at a very un-caterpillar time of year. But then, I’ve tried my hand at some unusual plants this year, interspersing a few herbs in my butterfly gardens.


Texas Master Naturalists generally promote native plants in order to help preserve our ancient local habitat for the bugs, birds, butterflies, moths and critters that call the Rio Grande Valley home. Although herbs aren’t native to the Valley, they, like many vegetables, can be grown here and complement and enhance both the garden and the food we eat.


In the garden, herbs can supply nectar and pollen to butterflies, bees and other insects. In addition, some herbs are host plants for butterfly caterpillars, like the common rue plant (Ruta graveolens), where I found my first out-of-season caterpillar. A small, slender black bug on a plant stem caught my attention. On close inspection, it was a dark caterpillar. I quickly identified it via www.iNaturalist.org as black swallowtail butterfly caterpillar.


Black swallowtail butterflies also use herbs from the Apiaceae, or Parsley family, as host plants, which include the herbs dill and common fennel. Butler’s sand parsley (Ammoselinum butleri), in the Apiaceae family, also is a host plant. It is a short-lived native annual that appears in spring in Cameron and Hidalgo counties.



Black Swallowtail Butterfly Caterpillar on Butler's Sand Parsley. (Photo by Anita Westervelt)

The herb, common rue, on the other hand, is in the Rutaceae, or Citrus family. Texas torchwood (Amyris texana), Sierra Madre torchwood (Amyris madrensis) and colima (Zanthosylum fagara) are three native trees in that family of plants that host swallowtail butterflies; the nonnative orange, lemon, lime and grapefruit trees popular in Valley gardens also are larval plants to some species of swallowtails.


I’d not seen the caterpillar of a black swallowtail in its early instar stages before. It was quite colorful with white half-circles for anklets, white stripes and splotches, and orange spots around its body and little black spines. It soon molted and changed to a smooth body with bold white stripes and black markings dotted with orange.


Black Swallowtail Butterfly Caterpillar on Rue. (Photo by Anita Westervelt)

Later stage Black Swallowtail Butterfly Caterpillar on Rue. (Photo by Anita Westervelt)

A tiny western giant swallowtail caterpillar also appeared on the rue leaves. Giant swallowtail larvae look like bird droppings – a disguise to discourage birds.


Giant Swallowtail Butterfly Caterpillar on Rue. (Photo by Anita Westervelt)

A third unseasonal find was a caterpillar I’d not seen before but have plenty of the butterflies: a white peacock caterpillar. This caterpillar was black with orange and black spikes that looked like transmission towers. It was munching through a leaf of native wild petunia (Ruellia nudiflora). White peacock butterflies also use the native plants Texas frog fruit (Phyla nodiflora) and herb-of-grace, also called coastal water hyssop, (Bacopa monnieri) as larval plants.


White Peacock Caterpillar on native Wild Petunia leaf. (Photo by Anita Westervelt)

Once caterpillars go through metamorphosis and emerge as butterflies, they need nectar. It’s important to have blooming plants ready for them. Currently, pink mint (Stachys drummondii), a winter-blooming native annual, is producing an abundance of blooms, providing nectar for several species of butterflies, including a monarch that’s been hanging around. Scorpion’s tail (Heliotropium angiospermum) is another important native butterfly nectar plant that blooms through the winter.


Monarch Butterfly draws nectar from winter-blooming native Pink Mint. (Photo by Anita Westervelt)

Winter-blooming Pink Mint provides nourishment for newly emerged White Peacock butterflies. (Photo by Anita Westervelt)