Friday, March 31, 2017

Leggy Bugs--Inchworms

Inchworms are caterpillars in the Geometridae family of Lepidopteran larvae, which I wrote about in “Leggy Bugs—Caterpillars (Lepidopteran Larvae, which Become Butterflies and Moths)”. They have front and back leggy sections and long middles—caterpillars' version of canines' dachshund.

Wisegeek’s “What Are Inchworms?” has an overview and an image for introduction for these critters. They're leggier than adult insects, but seemingly shortchanged compared to caterpillars in my previous article. (I used the picture as a basis for my blog image.)

For a more extensive introduction to inchworm and animal categorization, Bug Guide's website for “Family Geometridae - Geometrid Moths” is a good place to start.

Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Lepidoptera (Butterflies and Moths)
Superfamily Geometroidea (Geometrid, Swallowtail Moths)
Family Geometridae (Geometrid Moths)

Although inchworms are caterpillars, their locomotion is so odd that they deserve an article all their own. Their family, Geometridae, pertains to “earth” and “measuring”. Their physiology is more specialized than the caterpillars I wrote about previously. The Bug Guide explains:
the lack of prolegs in the middle of the body necessitates the peculiar method of locomotion, drawing the hind end up to the thoracic legs to form a loop, and then extending the body forward.
An excellent video of inchworm locomotion on a flat surface is “Inchworm Walking”. The caterpillar thrusts its front section forward, pulls the rear section up to the front legs, forming a loop, then repeats the motion. Its movement makes me think of a pelvis-shape strong enough to thrust out a very long torso and head. And yet, when fully extended, the head and front “arms” are strong enough to hoist the body and legs back to immediately behind the front end. The movement also seems like something a small, self-propelled slinky might make.

From Encyclopedia.com’s "Inchworm" description of inchworm movement:
inchworms lack appendages in the middle portion of their body, causing them to have a characteristic looping gait. They have three pairs of true legs at the front end, like other caterpillars, but only two or three pairs of prolegs (larval abdominal appendages), located at the rear end. An inchworm moves by drawing its hind end forward while holding on with the front legs, then advancing its front section while holding on with the prolegs.
The Bug Guide’s “Superfamily Geometroidea - Geometrid and Swallowtail Moths” provides most explanations and descriptions at the subfamily level.

Inchworms, unlike general caterpillars, metamorphose into only moths. Sciencing’s “Inchworm Life Cycle” explains:
The thousands of moth species in the family Geometridae are often referred to as inchworms when in the caterpillar stage. … This group of moths has a complete metamorphosis: They go through four stages during their life cycle.
More website resources:
Additional videos featuring inchworms and their movements, some with interesting sways:
  • "Inchworms"
    Ability to lift their front of the body at an angle as though bending from hips.
  • INCREDIBLE INCHWORM
    Acrobatic inchworm with hoisting its body almost totally vertical on horizontal surface and other seemingly gravity-defying surface grippings.
  • Inch worm Highway
    Inchworm walking the front legs forward, then dragging the rest of the body and rear legs forward. The body forms a loop as the rear section stops just behind the front legs.
  • Inchworm
    Another great example of locomotion, this inchworm being brown-patterned.
  • The Happy Inchworm
    Animation that shows motion as push from behind, pull from front, and no separate leg movement. This video is more for entertainment, although some commenters object to the violent outcome.

Leggy Bugs articles:

Saturday, March 25, 2017

Leggy Bugs—Caterpillars (Lepidopteran Larvae, which Become Butterflies and Moths)

Butterfly and moth caterpillars have fewer legs than the leggy bugs I wrote about last month (“Leggy Bugs--Centipedes and Millipedes”).

One nice image I found was helpful with identifiers. View a nicely captured example of movement at "Close-up Caterpillar Footage".

My image shows a caterpillar with two possible paths to adulthood of butterfly or moth. The pupa stage is chrysalis or cocoon. A butterfly emerges from a chrysalis, and a moth emerges from a cocoon. Their antennae and body shapes differ. Butterflies are active in the daytime, while moths are active at night.

North Carolina State University's "Lepidoptera" site succinctly describes the order that butterflies and moths belong to:
The name Lepidoptera, derived from the Greek words "lepido" for scale and "ptera" for wings, refers to the flattened hairs (scales) that cover the body and wings of most adults.”
The site includes basic information about the caterpillar life cycle and the adult stages as butterflies and moths. It also discusses animal classification terminology, noting that Lepidoptera is a category (order) under Insecta (class). It also summarizes subcategories (families) of lepidoptera. One family, Geometridae, includes inchworms. (Their locomotion is so weird to me that I'm going to save writing about them in my next article.)

I’ve always wondered about caterpillars having many legs, yet emerging as butterflies or moths after complete metamorphosis, with only six legs. For differentiation between complete (four-stage) and incomplete (three-stage) insect metamorphosis, visit the Pacific Science Center Exhibits “Metamorphosis” site.

Another curiosity for me is that “caterpillar” is their larval term, whether they emerge as either of the flying insects. Swithzoo’s "Caterpillar" site explains: “The caterpillar's six front legs transform into the adult insect's legs, the other 'prolegs' disappear, wings grow, and the insect emerges as a beautiful moth or butterfly.”

Purdue’s “Is It a Moth or Is It a Butterfly?” elaborates on the caterpillar’s prolegs and other characteristics:
Caterpillars have a well-developed head and a cylindrical body, which is made up of 13 segments. Each of the three segments behind the head has a pair of legs, just like adult insects. But caterpillars also have some additional, fleshy, leg-like appendages - called prolegs - on other segments. Prolegs have tiny hooks at the end that function to grasp things such as the stems and leaves of plants.
The Library of Congress site “How can you tell the difference between a butterfly and a moth?” provides loads of helpful, short, section titles about these insects (wings, anatomy, behavior, cocoon/chrysalis, …).

Backyard Nature's site "Caterpillars” shows an image that indicates the site’s focus on these animals’ voraciousness—webpage title imaged as leaves chewed into contours of “CATERPILLARS”. Visit for close looks and reads about these leggy bugs.

More resources:
  • GardeneGateeNotes “Cocoon versus chrysalis
    This site shows a cocoon and chrysalis side by side and provides a short, nuts and bolts explanation.
  • Diffen's "Butterfly vs. Moth"
    This site has a handy two-column table at the top, then more details and images. This site also includes a Related Comparisons section with links to pages comparing other related insects, other similar animals.
  • Easy Science for Kids "Butterflies and Moths"
    A table near the top shows differences between moths and butterflies, followed by basic text and a diagram (parts identified) for those who are just starting to look into these flighty insects.
  • Brittanica Kids site
    The main attraction is a helpful diagram of a butterfly and moth side-by-side and corresponding parts identifiers.
  • Kids' Inquiry of Diverse Species site for “Butterflies and moths
    This site’s format is question-and-answer, with basic and elementary approach.
  • Moths vs Butterflies
    Entertaining video (mostly narration) of basic contrasts between these flyers.

Leggy Bugs articles:
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