Northern Pink-striped Oakworm Moth



Northern Pink-striped Oakworm Moth, male
Photo by Brad Sylvester, copyright 2012.
Do not copy.

Some days I go out into my yard looking for a new species to chronicle in this blog. On other days, I just happen to run across interesting species serendipitously. On June 8th, I was out building a new shed when my son called me over to look at a moth that he found sitting on a piece of plywood we had lying on the lawn. It turned out to be a Northern Pink-striped Oakworm Moth (Anisota virginiensis virginiensis).

Moth or Butterfly?

It was one of the most colorful moths I had ever seen. Remember the checklist of butterfly versus moth traits I used to help identify the skippers (Hesperidae Family) last July? This one is not nearly as tricky as the skippers.

Northern Pink-striped Oakworm Moth
(Anisota virginiensis virginiensis)
Photo by Brad Sylvester, copyright 2012
Do not copy.

It has broad, feathered antennae, a large head, a thick, hairy body, and holds it wings flat and swept back while at rest. The bright colors and the fact that it was out and about during the daytime are the only traits which might suggest butterfly, but the others are far more accurate indicators. So we can be sure that it is a moth.

There are many, many species of moths and I certainly don't know them all or even a large percentage by sight. This one was knew to me, but was reminiscent of the Rosy Maple Moth. The Rosy Maple Moth is member of the taxonomic Family Saturniidae (Saturn Moths or Giant Silkworms and Royal Moths). Therefore, I started looking for a match at the Family level.

In reviewing images of the Rosy Maple Moth, I saw several photos of its larval form at bugguide.net and in my Audubon Field Guide. I recalled having seen a very similar early instar caterpillar on some oak leaves very near where this caterpillar was found. Perhaps then, instead of a Maple Moth it was some kind of Oak Moth. Using the search term "Oak Moth Saturnidae," I was able to find the Pink-striped Oakworm Moth (Anisota virginiensis), which has three sub-species.

Sub-species of Anisota virginiensis

The sub-species are most easily differentiated by the regions in which they live. In New Hampshire, we'd expect to find the sub-species Northern Pink-striped Oakworm Moth (Anisota virginiensis virginiensis). The Southern Pink-striped Oakworm Moth (Anisota virginiensis pellucida) lives from South Carolina to Florida and west to Louisiana according to Bugguide.net. While the Texas Pink-striped Oakworm Moth (Anisota virginiensis discolor) is found, as you may have guessed, in Texas.

Sexual Dimorphism

We know the species, and because the species, like human beings, is sexually dimorphic (the males and females look different), we can tell that the specimen I found in my yard is a male. Size is a key differentiator. The female is significantly larger than the male, but without one of each sex to compare, and without a tape measure handy, this is difficult to determine.

Hyaline Area

The lower wing edge is clearly
visible through the transparent
window of the hyaline area of
the male's forewing.
Photo by Brad Sylvester,
copyright 2012. Do not copy.

The other key trait used to determine the moth's sex is that males have a large clear "window" on the forewing (the larger wing on each side). You can literally see right through this part of the male's forewing. This is called a hyaline area. The female has no such clear patch.

Starvation Diet

Normally, I'd include dietary information in the Quick Facts section, but this one's pretty interesting. The larva of the species, called simply the pink-striped oakworm, eats oak leaves. If present in large numbers they can do consider damage to a tree's foliage. When they metamorphose into adult moths, however, do not eat at all according to butterfliesandmoths.org. Once they pupate, they begin to slowly starve to death as the stored fats retained from the caterpillar stage are used up.

Diurnal or Nocturnal?

I've already said the specimen of this moth that I found was out during the daylight hours, and I've identified it as a male. Males frequently fly during the day, seeking females by scent. Females, on the other hand, fly at night to find oak leaves suitable for egg-laying and can be attracted by light traps.

Quick Facts about the Northern Pink-striped Oakworm Moth:

Where does it live? Anisota virginiensis virginiensis ranges from Nova Scotia to North Carolina in the East and from Minnesota to Manitoba in the West.

Where does it go in winter? The Northern Pink-striped Oakworm Moth pupates in late fall and overwinters in the pupa just below ground according to butterfliesandmoths.org.

Habitat: Pretty much anywhere that oak trees are found from deciduous forest to city parks.

When is it here? Anisota virginiensis virginiensis does not migrate and is present here all year round. Its flight season, however, runs only from June to July in New Hampshire according to Bugguide, but as one goes farther south there may be two or even three generations each year depending upon how far south one goes. Of course, these are likely the Southern or Texas sub-species.

Lifespan: Up to one year, but perhaps only a few months in warmer climates.

Notes: Eggs are laid in bunches on the underside of oak leaves. According Forestryimages.org, they are spherical and yellow, laid in batches of several dozen at a time. Each egg is individually attached to the leaf.

Date found in my yard: June 8, 2012

Taxonomy of the Northern Pink-Striped Oakworm Moth:

Kingdom: Animalia (Animals)
Phylum: Arthropoda
Class: Insecta (Insects)
Order: Lepidoptera (Butterflies and Moths)
Family:Saturniidae (Silkworm Moths and Royal Moths)
Genus: Anisota
Species: Anisota virginiensis
Sub-species: Anisota virginiensis virginiensis

Butterfly or Moth? The Skipper Family (Hesperiidae) is a Little of Both

A member of the Grass Skipper family drinking nectar
Photo by Brad Sylvester, copyright 2011, all rights reserved

As we learn new skills, we keep them sharp by putting them to use. So let’s use our butterfly or moth checklist on this fellow.

First, it has a dull brownish color which would tend to make it a moth. It holds its wings upright when at rest which says butterfly. It is active in the daytime, which says butterfly, and the antennae are not feathery, but they end in a club-like thickening. The body is thick and hairy which says moth, and the head is oversized for a butterfly which says moth again. What do we do when our checklist of butterfly versus moth indicators is split down the middle?

While none of the checklist indicators are 100% accurate, because of some rare exceptions, the most accurate is the antennae structure. So, to start with, we’ll operate on the assumption that it’s a butterfly, but to be sure, let’s start at the Order level of Lepidoptera which includes both butterflies and moths since we’re certain that it’s one or the other.

There are two ways to start narrowing it down.  We can thumb through the butterfly and moth pictures in our field guide until we find a picture that matches or comes close. Using that method we find that the closest match is the silver-spotted skipper, but there are some distinct pattern and color differences which rule out this particular species, but there are enough shared traits that we start to focus on the skipper family which contains many different species, although my Audubon Field Guide details only a few.

My other favorite source is bugguide.net. From the main page, I click the butterfly picture on the graphic selection plate at the top left. That brings me to Papilionoidea (Butterflies excluding Skippers). Whoops. Let’s back up.  Near the top of this page there’s a complete taxonomic trail leading to Papilionidea. By choosing the next rung up the ladder, Order, we get to Lepidoptera (Butterflies and moths). About halfway down that page we get to Identification. Ah-ha! There are three listings: Moths, Butterflies, and Skippers. Although skippers are butterflies, they are a separate group with their own taxonomic family (Hesperiidae).

From there, I’m reasonably confident that it belongs to the sub-family of Grass Skippers (Hesperiinae). However, I can’t make a positive identification at a lower level than that. I can rule out many Grass Skippers, but I can’t pin it down. I think it is probably a Little Glassywing Skipper (Pompeius verna), but may be a Northern Broken-Dash Skipper (Wallengrenia egeremet). It looks very much like a three-spotted Skipper except the short antennae disqualify it as does the range. It looks like a Eufala Skipper as well, but again the range is a disqualifier.

• ·         NHPTV list of Skipper species that live in New Hampshire

Grass Skippers feeding on flowers in July
Photo by Brad Sylvester, copyright 2011, all rights reserved.

To make matters worse, I believe that I actually photographed as many as three separate Skipper species all flitting among the same flowers. I’ll detail the other two another day. There’s an old saying: Discretion is the better part of valor. Well, that saying applies equally well in trying to classify animals or plants. Sometimes you just can’t be sure based on the available information. That’s ok. A partial identification which gives the reasons why you can’t go further is better than making assumptions or guesses based on incomplete data.

Our taxonomic classification for the creature photographed on this page is:

Kingdom: Animals

Phylum: Arthropods

Class: Insects

Order: Butterflies and Moths (Lepidoptera)

Superfamily: Skippers (Hesperioidea)

Family: Skippers (Hesperiidae)

Subfamily: Grass Skippers (Hesperiinae)

Genus: either Pompeius

              Or  Wallengrenia

Species: either Little Glassywing Skipper (Pompeius verna)

                     Or   Northern Broken-Dash Skipper (Wallengrenia egeremet)

Miscellaneous observations:

These Grass Skippers are one of the few buterflies that actually make a buzzing sound when they fly at speed. This may have something to do with the wing arrangement. The fore and hind winds separate out and may be held at different planes while at rest. This posture is somewhat common among skippers, although it was rarely displayed among the group in my yard.

Grass skippers showing two different resting wing postures
Photo by Brad Sylvester, copyright 2011, all rights reserved

Quick facts about Grass Skippers:

Diet: Caterpillars eat grasses and sedges. Butterflies drink nectar - in my yard these species were dining on cone flowers (as show in the top picture) and appeared to prefer Blazing Stars Kobold (Liatris Spicata) where they were feeding in a group of about 15 or more individuals.
Range: varies by species
Habitat: Since the caterpillars feed on grass and sedges, they prefer open areas. Individual species may be particular about the specific species of grass that they eat.