Bug of the Month April 2011: Inchworm

Looper
Location: Fairfield, California
March 28, 2011 7:09 pm
Hi,
Every spring and summer I find these in our garden and would love to know what type of insect it is. Most recent find was on 3-26-11 on a Japanese maple, but I have found them on Lantana and also just hanging out on on the fence. I never see any feeding damage on the plants the looper is on. Thanks!
Signature: Sharon

Dear Sharon,
At the moment, we are only going to be able to provide you with a very general Family identification, which you may already know.  This is an Inchworm or Spanworm or Measuringworm in the family Geometridae, and browsing through BugGuide will reveal many similar looking caterpillars.  Inchworms are also sometimes called Loopers, though not all Loopers are in the family Geometridae.  The Inchworm gets its common name because of its manner of locomotion, which your photo beautifully illustrates.  Most caterpillars have five pairs of prolegs, but Inchworms have only two pairs, which results in the caterpillar walking forward with the fore part of the body in a typical manner, and then looping the rear portion of the body to catch up, causing the larva to appear as though it is measuring distance as it moves.  Your second photo demonstrates the marvelous camouflage ability these caterpillars have for mimicking small twigs.  We are not certain what species of Inchworm you have submitted, but we suspect the species found on the Lantana might be different from the individual you found on the maple.  Many Inchworms look very similar and they are difficult to distinguish from other members of the family.  Since it is the end of March, it is time for us to select a Bug of the Month for April, and we love your photos so much, we have decided to give your Inchworm that honor.  With the dormant trees beginning to produce tender leaves in many parts of the country, young caterpillars will start appearing as well to feed on those leaves.  The vast majority of our caterpillar submissions occur in the fall when large fully developed Caterpillars leave their host plants to find places to pupate, but sharp eyed observers will be able to find Caterpillars in the spring as well.

Hi Daniel!
I am absolutely thrilled (can’t stop smiling) that you have chosen my submission as worthy for BOM! I am a “wannabe” entomologist, to the point that I lead the introduction to entomology for my county’s Master Gardener training class. I am a certified Master Gardener and photography is another of my hobbies. I hope to culture this inchworm through to its adult stage (to help in the identification). I have tried before, but my captive conditions do not seem suitable for success. Perhaps a larger terrarium with native soil will help.
And thank you for the lesson on inchworm definition (vs. caterpillar), I will share this information with my Master Gardener peers and trainees! Thank you, again!
Cheers!
Sharon Leos