Maier, C.T.; Lemmon, C.R.; Fengler, J.M.; Schweitzer, D.F.; Reardon, R.C.; Caterpillars on the Foliage of Conifers in the Northeastern United States. Morgantown, WV. USDA Forest Service. Forest Health Technology Enterprise Team Connecticut Agricultural Experiment Station. FHTET-2004-01. March 2004. 151 p.
Moths and butterflies (Order Lepidoptera) whose caterpillars consume the foliage of northeastern conifers have an enormous
diversity of life styles. Most species have one or two generations per year. They develop through four life stages: the egg, the caterpillar or the larva, the pupa (chrysalis in butterflies), and the adult (moth or butterfly). In Lepidoptera, the caterpillar and the adult usually are markedly different in appearance and function. The caterpillar principally feeds and grows, whereas the adult mainly reproduces and disperses. The transformation from the caterpillar to the adult moth or butterfly
takes place during the pupal stage. Most of the species that are restricted to conifers spend the winter as an egg, a caterpillar, or a pupa; very few species pass the winter as an adult.
Lepidoptera differ in the duration of their life stages. In the Northeast, the stage that exists during the late fall and winter typically lasts the longest because development slows or stops during periods of low temperature. Eggs that are laid during the spring and the early summer usually hatch in 1 to 3 weeks. After hatching from eggs, caterpillars feed for variable amounts of time, but most reach full size within 1 to 3 months. Most caterpillars molt or "shed their skin" four to six times. Between molts the caterpillar is considered an instar, with the number of the instar increasing with age. Caterpillars can grow because the body covering or cuticle increases in size with each successive molt. Pupae that do not delay development normally yield adults in 1 to 4 weeks.
In general, caterpillars restricted to conifers eat species in only one to a few genera. Perhaps, the most restricted in diet are the tiny caterpillars that exclusively mine needles to obtain food for development. Most of the needleminers eat trees in only one genus and sometimes in only one species of that genus. Among the larger caterpillars on pines, certain species of Macaria (Family Geometridae) and Zale (Family Noctuidae) are restricted to one or more pines, Pinus species. A narrow diet also can be found among caterpillars that eat other types of conifers. Even among the conifer feeders, however, a few species will eat the majority of native species growing within their distributional range.
In New England, where our sampling was concentrated, there are 16 native species of conifers in three plant families. These families and species are:
Pinaceae (firs, pines, spruces, and relatives)
Balsam fir, Abies balsamea
Eastern larch, Larix laricina
White spruce, Picea glauca
Black spruce, Picea mariana
Red spruce, Picea rubens
Jack pine, Pinus banksiana
Red pine, Pinus resinosa
Pitch pine, Pinus rigida
Eastern white pine, Pinus strobus
Eastern hemlock, Tsuga canadensis
Taxaceae (yews)
Canadian yew, Taxus canadensis
Cupressaceae (cedars, false cedars, and junipers)
Atlantic white-cedar, Chamaecyparis thyoides
Common juniper, Juniperus communis
Creeping juniper, Juniperus horizontalis
Eastern red-cedar, Juniperus virginiana
Northern white-cedar, Thuja occidentalis
We generally do not list non-native food plants of caterpillars mentioned in this guide, although exotic conifers found in plantations, in yards, or along roads may be suitable food. We did not collect caterpillars on Canadian yew or creeping juniper, and infrequently sampled those in natural stands of black spruce, jack pine, and red pine. In addition, we did not sample or list native food plants that are absent or scarce to the north of southern New Jersey or Delaware. Examples of these include shortleaf pine, Pinus echinata, pond pine, P. serotina, loblolly pine, P. taeda, Virginia pine, P. virginiana (Pinaceae), and bald cypress, Taxodium distichum (Taxodiaceae).
The monarch butterfly life cycle is divided into 4 main stages: egg, caterpillars, chrysalis, and butterfly.
Since Caterpillars grow approximately 3000% during this stage of monarch metamorphosis, the caterpillar life cycle phase is subdivided into 5 stages, known as instars.
1st Instar Monarch Caterpillar
2nd Instar Monarch Caterpillar
3rd Instar Monarch Caterpillar
4th Instar Monarch Caterpillar
5th Instar Monarch Caterpillar
Next Instar Signs?
The measurements listed below are rough estimates of caterpillar instar sizes but caterpillars will vary in size depending on genetics, and how much milkweed they eat.
Instar 1 Monarch Caterpillar Body Length- 2mm to 6mm (<.2 inches)
The hatchling first emerges, only to turn back around to devour its nutrition-laced eggshell, or chorion. Soon after, it will feed in a circular pattern on top of the leaf, as its mandibles (jaws) are too small to cut the sides of a leaf.
See Instar 1 caterpillar feeding pattern on milkweed leaves
A hatchling monarch caterpillar is so small it can barely be seen by the naked eye. With magnification, you can also see tiny dark hairs on the caterpillar, called setae.
Even magnified, it won‘t resemble the vibrantly-colored caterpillar you’re familiar with because:
- The head is fully black.
- The telltale stripes are absent from the tiny gray caterpillar
- The filaments (antennae-like structures on the front and back of the caterpillar) are baby bumps.
Caterpillar Life Cycle Instar ONE duration: approx 1 to 3 days
Raising Tip: If you’re interested in getting a closer look at 1st instar caterpillars, try a handheld magnifying glass.
The entire monarch caterpillar life cycle lasts
approximately two weeks, but can take more or less time depending on temperature and light conditions it’s exposed to.
More heat/light= faster caterpillar life cycle
Less heat/light= slower caterpillar life cycle
Instar 2 Monarch Caterpillar Body Length- 6mm to 9mm (.2 to .4 inches)
The monarch caterpillar stripes become fully visible, but the black stripes are often so thin,
the caterpillar appears very light in color. Some monarch enthusiasts affectionately refer to them as blondes.
During the first two instars, a monarch caterpillar eats very little and will still be munching (slowly) away on its first leaf.
During the second instar, you’ll notice the distinctive yellow and black facial markings appear (see instar 3)
Caterpillar Life cycle Instar TWO duration: 1 to 3 days
Raising Tip: If you'e wondering when to transfer monarch caterpillars from a sealed food container to a mesh cage, the short answer is when you can easily see them. For most, that's monarch caterpillar instar 2 or 3:
More info on transferring baby caterpillars to a new habitat cage.
Instar 3 Monarch Caterpillar Body Length- 10mm to 14mm (.4 to .6 inch inches)
During
instar stage 3, the fast-growing caterpillar is able to eat through the entire leaf.
As the caterpillar develops, it becomes more sensitive to sound and will violently jerk its head back when disturbed…or if you ‘HOOT’ like an owl 🦉
Caterpillar Life Cycle Instar THREE duration: 1 to 3 days
Instar 4 Monarch Caterpillar Body Length- 13mm to 25mm (.6 to 1 inch)
The black stripes of the caterpillar get thicker and more prominent as the caterpillar continues to grow.
The very hungry caterpillar becomes just that and starts mowing mown multiple milkweed leaves. 🌿🐛
Caterpillar Life Cycle Instar FOUR duration: 1 to 3 days
Raising Tip:
9 Ideas for when you run out of milkweed?
Instar 5 Monarch Caterpillar Body Length- 25mm to 45mm (> 1 inch)
The filaments will grow longer throughout the caterpillar’s development. Even though they are antennae-LIKE, these are not the actual antennae of the adult butterfly and they will be shed when the caterpillar pupates.
The caterpillar filaments are sensory organs that can guide the sight-challenged caterpillar to milkweed, or to the perfect place to form it’s chrysalis:
Long Filaments of a 5th Instar Caterpillar
The caterpillar antennae are much smaller, and located near the mandibles (jaws) of they caterpillar. They help find milkweed through scent.
Caterpillar Life Cycle Instar FIVE duration: 3 to 5 days
Signs a Monarch Caterpillar is about to Molt to the next Instar?
- When a caterpillar molts (sheds its skin), it also loses its head capsule. Check out a pre-molt before and after head capsule photo
- Raising Butterflies? If a caterpillar crawls on to a mesh cage wall, its typically positioned facing down when it’s preparing to molt.
Freshly Molted Monarch
Raising Monarch Caterpillars Tip:
Moving pre-molt monarchs by hand can hurt or even kill them. If you’re concerned a wayward caterpillar won’t find it’s way back to milkweed after molting, simply move your floral tube rack (filled with milkweed cuttings) close to the caterpillar so it can easily crawl to milkweed after it’s graduated to the next instar.
More info on setting up milkweed stem cuttings to feed monarch caterpillars throughout the monarch caterpillar life cycle