Don’t Touch Buckmoth Caterpillars

Buckmoths (genus Hemileuca, several species) are found across southern Arizona, New Mexico, and Texas, and south through Sonora and Chihuahua, Mexico. Habitat varies from mesquite bosques to grasslands and plains, depending on the species. They feed on the leaves of palo verdes, mesquites, and other desert trees. The spines of the caterpillars can release a very painful toxin, so don’t touch them.

The following material is from a publication of the Arizona-Sonora Desert Museum which was derived from: Tread Lightly: Venomous and Poisonous Animals of the Southwest, by Rich and Margie Wagner. Rio Nuevo Publishers, Tucson, AZ. 2005. Reprinted with permission of ASDM.

Physical Characteristics

A number of caterpillars have developed an effective form of chemical defense that utilizes “stinging spines” on their bodies to ward off would-be predators. The most common of these are the buckmoth caterpillars, of which about 23 species are found in the Southwest. The full-grown caterpillars are about 2 inches long (5 cm) and are covered from one end to the other with bristles or urticating spines. The colors are variable and depend on the species. The fast-flying adult moths have a wingspan of about 2-3 inches (5-7.5 cm), and vary in color from relatively nondescript tan and brown to brilliantly colored yellow and orange on black. They are primarily day-fliers, and they do not have stinging spines. (Urticating: cause a stinging pain or sensation)


Juno Buckmoth (Hemileuca juno) caterpillars feed on the leaves of common desert trees, often in groups. When molested, the caterpillar usually stops feeding and remains motionless, counting on camouflage and the urticating spines for protection. Caterpillars occasionally drop off branches and land on people, or are brushed against by riders on horseback, resulting in envenomation by the urticating spines. Other buckmoth caterpillars, like those of the range caterpillar moth (Hemileuca oliviae), feed on grasses, and envenomations can inadvertently occur when a person is walking through the grass.


The life cycle of moths is somewhat complex, and the particular details are species-specific. Flights generally occur from September through December. The mating of most Hemileuca moths, such as the Juno or mesquite buckmoth, begins shortly after sunset on fall evenings. Males use their well-developed antennae to track and follow the pheromone trail given off by female moths. After mating, the female deposits eggs on branches in host trees, with the eggs usually laid in circles around small branches. The eggs over-winter and hatch in April or May into small larvae, or caterpillars, that eat and grow for about a month, molting through five instars before they migrate to the ground and form a pupa, or cocoon, in leaf litter. After metamorphosis, most of the cocoons will hatch into adults (in the fall again), although some Hemileuca cocoons have been known to lie dormant for four years.

Effects of venom

The spines of stinging caterpillars contain toxins that are produced in gland cells. Caterpillars do not have a stinging apparatus per se, but rather depend on intentional or inadvertent contact of the spines with the skin of a victim. After the spines penetrate the skin, they break off, releasing toxins that cause mild to severe pain and other compounds that induce an inflammatory dermatitis called erucism. Because the protein components of the toxins are considered “foreign” to the body, an allergic reaction may also occur. While hospitalization is rarely required for stings on the skin, spines that enter the eyes may cause potentially serious complications.

First Aid and Medical Treatment

Anyone attempting to remove a stinging caterpillar should be careful not to incur additional stings on the hands or elsewhere, particularly as the caterpillar drops off. Wash the area immediately with soap and water. Spines that remain in the skin can often be removed with adhesive tape. Baking soda applied as a paste with water may help decrease the pain, as may ice applied to the injured area. Acetaminophen or ibuprofen may be taken for pain. Benadryl® may help treat localized allergic reactions. As always, victims with severe allergic reactions should seek immediate medical attention, as should anyone with persistent symptoms or signs of infection.

The moths, themselves, are harmless.

Buckmoth caterpillars are especially abundant in New Orleans and tend to fall out of oak trees onto unwary people. (See video about “the attack of the buckmoth caterpillars”) There are several other stinging caterpillars; see this from the Florida Poison Information Center.

See also:


Sphinx Moths

Sphinx moth adult

Sphinx moth caterpillar

Sphinx moths (also called hawk moths and hummingbird moths) belong to a large family, Sphingidae, with about 1450 species. These are large moths with wingspans up to six inches.

Most common in the Tucson area is the White-lined sphinx moth (Hyles lineata) which has a wingspan of up to 5 inches and a body length of up to 3.5 inches. Its range extends from Central America, throughout the U.S. and into southern Canada. These moths are often mistaken for hummingbirds at first glance because they are about the same size and behave much like hummingbirds. They are fast flyers and can hover at a flower to sip nectar with their very long tongues; and they can fly side-to-side, and backwards. These moths are mainly nocturnal but may be about during daylight hours. The first generation adults appear in mid-May, with subsequent generations appearing throughout the summer. See good close-up photos of the adult moth and caterpillar here.

Life cycle:

Adults females lay eggs generally on the underside of leaves upon which they feed. The eggs hatch into the larval stage – caterpillars. The sphinx moth caterpillar, which can be up to 5 inches long, is generally bright green with dark spots, but it can also be almost completely black or striped yellow and brownish. It has a large (harmless) hook on its back end similar to a tomato “hookworm.” According to DesertUSA, the name “sphinx moth” derives from the behavior of the caterpillar. “When alarmed, these larvae rear up their heads in a threatening sphinx-like posture and may emit a thick, green substance from their mouths.”

To complete pupation, the caterpillars dig burrows. Pupation can last from two weeks to several months depending on species and conditions. The adults moths dig themselves out from underground and may mate soon thereafter. According to DesertUSA, “In the Sonoran and Chihuahuan deserts, there may be two broods, one in the spring and another in summer. In the colder Great Basin desert, only one brood is produced.” In some species, if pupation begins in the Fall, it will last all winter with adults emerging in the Spring.

The moths feed exclusively on nectar and seek out flowers which have large supplies. This includes the evening primrose (see my ADI primrose article and a photo of the long tongue of a sphinx moth.) Some species can be harmful to crops.

According to a study at the University of Arizona, the Tohono O’odham would harvest the caterpillars, dry and braid them and use them as food. The study says that the caterpillars are not poisonous, but warns that eating too many will result in an upset stomach. (It doesn’t say how many are too many.)