The FINANCIAL - Caterpillars with venomous spines appeared in eastern Virginia counties

Caterpillars with venomous spines appeared in eastern Virginia counties

Caterpillars with venomous spines appeared in eastern Virginia counties

The FINANCIAL -- VDOF’s forest health team has received reports of the puss caterpillar in a few eastern Virginia counties. The "hairs" of this caterpillar are actually venomous spines that cause a painful reaction if touched.

The caterpillars eat oak and elm leaves, but they can be found in parks or near structures. If you find the caterpillar, leave it alone and let its natural enemies control their populations— there are a number of other insects that will prey on them at different stages of their life cycle.

Micks (1956) reported a parasitization rate of 20% in a population of Megalopyge opercularis in Galveston, Texas. There are similar rates of parasitism in Central Florida (DW Hall, unpublished data).

There are at least two ichneumonid wasp (Hymenoptera: Ichneumonidae) parasitoids of Megalopyge opercularis:

Hyposoter fugitivus (Say)
Lanugo retentor (Brulle)

Hyposotor fugitivus attacks and kills young larvae (Khalaf 1977). Lanugo retentor oviposits through the wall of the cocoon and is parasitic externally on prepupae or pupae (Khalaf 1975, Khalaf 1981). Full-grown Lanugo larvae make their own cocoons inside the Megalopyge cocoons and when mature, the adult wasps chew their way out of both cocoons making holes of 2-3 mm diameter. The holes in the Megalopyge cocoon are often, but not always chewed through the operculum.

The family name Megalopygidae and genus name Megalopyge are derived from the Greek roots Megalo (large) and pygidium (rump) - probably because of the shape of the caterpillars. The specific epithet, opercularis, is derived from the Latin word operculum (Borror 1960) and refers to the lid (door) on the cocoon. The name “puss caterpillar” is likely in reference to the caterpillar’s resemblance to a cat with its soft fur and tail.

The southern flannel moth was originally described by J. E. Smith (1797) and named Phalaena opercularis (common name, waved yellow egger moth). For a historical account of the southern flannel moth’s taxonomy see Heppner (2003). In addition to the name “puss caterpillar”, its caterpillar has been called “Italian asp,” “possum bug,” “perrito” (Spanish for puppy or little dog) (Bishopp 1923), and “woolly slug” (El-Mallakh et al. 1986).

The southern flannel moth is the most common of the five species of megalopygids found in the southeastern United States.

The southern flannel moth is found from New Jersey to Florida and west to Arkansas and Texas (Covell 2005). It is common in Florida but reaches its greatest abundance in Texas from Dallas southward in the western central part of the state (Bishopp 1923).

Adults: Adults are small moths with wingspans of 2.4 to 3.6 cm (approximately 1 to 1.5 in) (Covell 2005). Females are larger than males. The front wings are yellow with some black along the costal margins and waves of white hair-like setae (scales) on the basal 2/3 of the wings. Khalaf (1984) demonstrated that the hair-like setae are actually deeply divided scales and that the undivided bases of the scales are typical of wing scales of other moths. The black color is more pronounced in males. Hind wings of both sexes are uniformly creamy-yellow. The common name “flannel moth” is due to the thick coating of fur-like setae on the bodies which is predominantly orange on the thorax.
Larvae: The number of instars is uncertain and may be variable. Bishop (1923) stated that there are probably five or six instars. and gave the following approximate lengths for the first four and last instars: 1st instar: 1.5 mm, 2nd instar: 2.3 mm, 3rd instar: 3.1 mm, 4th instar: 3.6mm, mature larva: 2.54 cm (1 inch). Davidson (1967) reported similar dimensions. It seems that there may have been a misidentification of later instars by these authors based on the huge size difference reported between the fourth and final instars. Khalaf (1975) reported that there are 8 to 10 instars.

Full-grown larvae, including the ones in Figures 13 to 15 reared by the author on winged elm, Ulmus alata Michaux, were much larger and measured approximately 3.5 cm (1.4 inches) in body length and 4.0 cm (1.6 inches) including the tail.

The integument of first and second instars is yellow but becomes pale greenish white to white in later instars. Larvae become progressively more “hairy” with each molt. All instars have rows of verrucae (raised sclerites with radiating setae [Gordh and Headrick 2001]) that bear hollow spines each of which has a venom gland at its base (Foot 1922). The spines are obscured by the long soft setae in the late instars. Late instars have a hairy tail. The color of late instars is somewhat variable.

Unlike most other moth larvae, megalopygid larvae have seven pairs of prolegs. Megalopygids have accessory prolegs on abdominal segments two and seven in addition to the normal complement of prolegs on abdominal segments three through six and ten. The accessory prolegs of all North American species of megalopygids, including the puss caterpillar, have no crochets (Stehr 1987, Wagner 2005).

Megalopygid larvae also have post-spiracular appendages (Figure 26) (=digitate sensilla of Epstein [1996]) on the abdominal segments that are hidden by the thick coat of setae. A defensive function was assigned to these structures by Hoffman (1932 [cited by Epstein 1996]) who reported that stimulation in the area of the “sensilla” resulted in the larva moving both the sub-dorsal and lateral spine-bearing verrucae toward the spiracles.

Occasionally, in outbreak years, puss caterpillars are sufficiently numerous to defoliate some trees (Bishopp 1923). However, their main importance is medical. In Texas, they have been so numerous in some years that schools in San Antonio in 1923 and Galveston in 1951 were closed temporarily because of stings to children (Diaz 2005).

The venomous spines of puss caterpillars are hollow and each is equipped with a venom gland at its base (Foot 1922). All larval instars, as well as exuviae, may sting but the toxicity of the stings increases with increasing size of the larvae (Davidson 1967).

Foot (1922) reported that some individuals react more severely to stings than others, and the severity of the sting varies with the thickness of the skin where the sting occurs The sting produces an immediate intense burning pain followed the appearance of a red grid-like pattern on the skin that matches the pattern of the venomous spines on the caterpillar. Swelling and sometimes also lymphadenopathy follow.

In addition to the characteristic localized symptoms, more general systemic manifestations may also occur including headache, fever, nausea, vomiting, tachycardia, low blood pressure, seizures and more rarely, abdominal pain, muscle spasms and convulsions (Diaz 2005, Eagleman 2008, El-Mallakh et al. 1986, Hossler 2010, McGovern 1961, Pinson and Morgan 1991).

The venom is not well-characterized but it has been shown to possess hemolytic activity, and there is evidence that it is proteinaceous based primarily on its precipitation by 75% saturated ammonium sulfate and the fact that it is inactivated by digestion with proteolytic enzymes (trypsin, pepsin, or chymotrypsin) (Picarelli and Valle 1971).

Eagleman (2008) has reviewed common treatments for puss caterpillar stings. Remedies that may be helpful in some cases include removing broken spine tips from the skin with tape, applying ice packs, use of oral antihistamine, application of hydrocortisone cream to the site of the sting, systemic corticosteroids, and intravenous calcium gluconate.

Natural Enemies (Back to Top)

Khalaf (1975) observed Chrysopa sp. (Neuroptera: Chrysopidae) feeding on eggs and early instars. Khalaf (1975) also observed an Anolis lizard eat a 4th instar larva (about 5 mm long) after which it displayed gulping motions and rubbed its mouth against the ground. Larvae are probably attacked by a variety of generalist predators, but reported observations are lacking. Older instars are likely well-defended from vertebrate predators by their venomous spines.

At least four species of tachinid flies (Diptera : Tachinidae) have been reported from Megalopyge opercularis (Arnaud 1978, Khalaf 1975, Micks 1956, Patton 1956). O’Hara (2013) has updated the tachinid names from Arnaud (1978).

Micks (1956) reported a parasitization rate of 20% in a population of Megalopyge opercularis in Galveston, Texas. There are similar rates of parasitism in Central Florida (DW Hall, unpublished data).

There are at least two ichneumonid wasp (Hymenoptera: Ichneumonidae) parasitoids of Megalopyge opercularis:

Hyposoter fugitivus (Say)
Lanugo retentor (Brulle)

Hyposotor fugitivus attacks and kills young larvae (Khalaf 1977). Lanugo retentor oviposits through the wall of the cocoon and is parasitic externally on prepupae or pupae (Khalaf 1975, Khalaf 1981). Full-grown Lanugo larvae make their own cocoons inside the Megalopyge cocoons and when mature, the adult wasps chew their way out of both cocoons making holes of 2-3 mm diameter. The holes in the Megalopyge cocoon are often, but not always chewed through the operculum.

Author: The FINANCIAL