UMass Garden Calendar Photo Contest
Ever take a great garden photo and think “this would be perfect for the UMass Garden Calendar?” We're holding a photo contest for the 2019 UMass Extension Garden Calendar, so have your camera handy and keep an eye out for contest-worthy pics! The deadline for submitting pictures is April 1, 2018. Submission details are at https://ag.umass.edu/landscape/publications-resources/garden-calendar/garden-calendar-photo-contest.
Fantastic and Self-Defended Caterpillars
The immature insects that are frequently referred to as caterpillars primarily include species in the Lepidoptera (butterflies and moths) and Hymenoptera (specifically, sawflies) families. A gardener becomes well acquainted with the caterpillars of many of the sawflies, moths, and butterflies when trying to determine “who” has been munching on the leaves of their prized plant(s) in the landscape or just by being in the right place at the right time. While some of the larval sawflies can be serious pests of landscape trees and shrubs, we'll focus here on a handful of species of butterflies and moths that have been spotted and reported in Massachusetts in August and September. According to Caterpillars of Eastern North America by David L. Wagner, close to 13,000 species of butterflies and moths occur north of Mexico, with approximately 5,000 of those occurring east of the Mississippi River. The few species discussed here are natives found in Massachusetts and they employ fascinating mechanisms for self-defense.
Looking Like Bird Droppings and Hidden Osmeteria
The above title may sound like a really good insult, but mimicking the droppings of a bird allows some species of caterpillar the luxury of hiding in plain sight. What self-respecting predator wants to eat bird excrement anyway? The very young caterpillars of the eastern black swallowtail (Papilio polyxenes) are bird dropping mimics. They are mostly black with a white “saddle” or marking that lends itself to providing the aforementioned camouflage. Older caterpillars of this species, also referred to as parsleyworms due to their favored host plants, are arguably more attractive. As seen in these photos, these caterpillars are mostly green with black stripes and yellow spots. Caterpillars of this species often feed on cultivated carrots, dill, and parsley. This insect is one of the most common and most studied swallowtails in North America. It is found in southern Canada, the eastern and mid-western USA, further west to the Rocky Mountains, and into northern Mexico. Because this insect shares the same palate for certain cultivated items such as herbs found in our gardens, there are some who may view these gorgeous caterpillars as pests. They have tachinid fly and hymenopteran (wasp) parasitoids as natural enemies. The adult butterfly is one of our largest and arguably one of our most attractive insects. When at all possible, resist the urge to kill or remove parsleyworms. These caterpillars are typically not in large enough numbers to truly cause a problem. If you do grab a mature parsleyworm caterpillar, be prepared for the osmeterium. This is a brightly colored, often orange-yellow organ that the larva will protrude from its first abdominal segment in a defensive display. The osmeterium is not harmfule but is often coated in a smelly chemical deterrent that the insect attempts to coat the assailant with in self-defense.
A perhaps more convincing bird dropping mimic, the caterpillars of Papilio cresphontes are the immature stage of the giant swallowtail butterfly. This insect is widely distributed throughout the United States and much of North, Central, and South America. Host plants include members of the Rutaceae (citrus) family, including but not limited to prickly ash (Zanthoxylum spp.), torchwood (Amyris spp.), and hoptree/wafer ash (Ptelea trifoliata). The caterpillars pictured here were collected from wafer ash on 9/21/17 in Amherst, MA. These caterpillars may partially defoliate small, potted plants but are otherwise not problematic. They may be considered minor pests in certain Citrus spp. crops. The adult butterflies of this species sip nectar from flowering plants such as azalea, Japanese honeysuckle, goldenrod, and swamp milkweed but can be common to many flowering plants. The adult butterfly is quite the attractive swallowtail; however, these caterpillars can be appreciated as well. Commonly referred to as the orange dog caterpillar (or orange puppy depending on who you ask), these larvae possess iridescent
sapphire-blue spots and defense-related patterns: bird dropping-like markings coupled with what some call snake-mimicry. Scale-like markings, like those of a snake, can be seen on more mature caterpillars near the thorax. But perhaps the most impressive defense mechanism of all is the bright red osmeterium that the caterpillar will exude when irritated. This structure may look like the forked tongue of a snake, but it is again a gland that contains a mixture of chemicals that produce a putrid smell but is not harmful. This pungent aroma has been described by some as similar to that of “rancid butter”. The aroma is certainly unpleasant and surprisingly strong in this particular species.
Irritating Hairs, Spines, and Warning Coloration
The caterpillars of the hickory tussock moth are easily recognizable. Unlike the two species discussed above, they are occasionally able to strip trees of their leaves, perhaps due to the larger number of eggs laid together. Lophocampa caryae is native to southern Canada and the northeastern United States. There is one generation per year. Overwintering occurs as a pupa inside a fuzzy, oval shaped cocoon. Adult moths emerge approximately in May and their presence can continue into July. Females will then lay clusters of 100+ eggs together on the underside of leaves. Females of this species can fly; however, they have been called weak fliers due to their large size. When first hatched from their eggs, the young caterpillars will feed gregariously in a group, eventually dispersing and heading out on their own to forage. Caterpillar maturity can take up to three months and color changes occur during this time. These caterpillars are essentially white with some black markings and a black head capsule. They are very hairy, and should not be handled with bare hands as sensitive individuals can have skin irritations or rashes (dermitis) as a result of interacting with hickory tussock moth hairs. By late September, the caterpillars create their oval, fuzzy cocoons hidden in the leaf litter where they overwinter. Hosts whose leaves are fed upon by these caterpillars include but are not limited to hickory, walnut, butternut, linden, apple, basswood, birch, elm, black locust, and aspen. Maple and oak have also been reportedly fed upon by this insect. Several wasp species are parasitoids of hickory tussock moth caterpillars.
The caterpillars of the giant leopard moth (Hypercompe scribonia) seem to be the embodiment of the phrase: "GO AWAY". This species is native to New England with a large geographic range from southern Canada to Florida. One could argue that they are in their own way
beautiful. Sharp, stiff bristles or spines provide physical protection, especially when the caterpillar is disturbed, which causes the insect to roll into a defensive position. Once curled up, as seen in these photos, the red rings between the segments of the body become visible. The spiracles, or external respiratory openings, of these caterpillars are also red in color. These bold markings suggest to the onlooker that this caterpillar is also chemically protected (meaning they would be distasteful or potentially poisonous if consumed by a predator). These larvae feed on both woody and non-woody plants, including but not limited to cherry, willow, oak, plantain, sunflower, violet, and dandelion, although the feeding damage they cause does not warrant management. As was the case with this individual found in Hampshire County, MA on 9/23/17, the nearly fully-grown caterpillars of this species are frequently encountered by people raking leaves or busy with fall cleanup of landscaped areas. These caterpillars overwinter in sheltered areas such as leaf litter, under logs, or beneath loose bark.
If you are interested in learning more about the caterpillars of butterflies and moths, the aforementioned field guide, Caterpillars of Eastern North America by David L. Wagner is a beautifully illustrated text with great information. Online resources abound, including the Lepidopterists’ Society (www.lepsoc.org), the North American Butterfly Association (www.naba.org), the Massachusetts Butterfly Club (www.naba.org/chapters/nabambc/index.asp), and the Butterflies and Moths of North America (www.butterfliesandmoths.org).
Tawny Simisky, UMass Extension Entomologist