Spanworms on Maine Cranberries

CRANBERRIES

Spanworms
Order: Lepidoptera || Family: Geométridae
NOTE: The terms spanworm, inchworm, looper, and geometer, are all synonymous.

Spanworms (Family Geométridae), many of which find cranberry foliage tasty, make up the second largest family of Lepidoptera in eastern forests. Many of them find themselves in cranberry beds by accident, having been deposited there by the wind. As a rule, they are masters of camouflage—mimicking foliage, sticks, petioles, and other plant parts. With but a few exceptions, all can be readily recognized by the possession of only a single pair of mid-abdominal prolegs. Being so endowed, they tend to loop rather than crawl, hence the term, ‘looper’. During three of the last 12 years (1999, 2001 & 2002), high spanworm populations were observed on Maine cranberry beds. The most problematic years were 2001 and 2002, with 33% of monitored sites surpassing the Action Threshold (AT) in 2001, and 19% of sites surpassing the AT in 2002. The key factor appears to be the weather. Each of the three high-spanworm summers were very hot and dry, just the way spanworms and many other non-aquatic insects like it. The summers of 1999, 2001 and 2002 had 17% below normal rainfall, 22% below normal rainfall, and 20% below normal rainfall, respectively. 2001 saw Maine’s 13th driest summer on record since 1895, and 1999 and 2002 tied for a ranking of 15, where 1 = the driest and 108 = the wettest. Many spanworm caterpillars first appear in early-season sweeps (late May to early June). Newly-hatched spanworms cling to the inside of the sweep net. Be aware of spanworm infestations during bloom. They may be quite clumped in patches throughout the bed.

Green Spanworm - Itame sulphurea (Packard): This spanworm hasn’t been found in very high numbers thus far on Maine cranberry beds, but is capable of doing considerable harm. The action threshold (AT), however, is different from all of our other spanworms (18 per 25 sweeps). Where it is often found in combination with other spanworms, though, I believe using an AT of 4.5 (or 9 depending on berry price) per 25 sweeps makes management easier and safeguarding the crop less risky. It is still seen in very high numbers on a few Massachusetts bogs, and in 1920 and 1921, it devastated the entire crop on a very large scale for many Massachusetts growers. [See also pages 27-28 of Cranberry Insects of the Northeast by A.L. Averill & M.M. Sylvia]

Horned Spanworm - Nematocampa resistaria: This peculiar-looking spanworm is unmistakable with its double set of dorsal white-tipped tentacles (‘horns’) on the 2nd and 3rd abdominal segments. Besides eating cranberry, it feeds on many softwood and hardwood trees and goes through two generations in our part of the country. So far, it has been found only occasionally on Maine cranberry beds.

Chainspotted Geometer - Cingilia catenaria (Drury): This spanworm is most often found in low numbers on Maine cranberry beds. It may be on the rise, however, and a very high population of moths were observed on a cranberry bed in Washington County in early October, 2004. Literature from an entomologist (Baker) from 1972 says that the species prefers blueberries, huckleberries, and small trees growing in pastures or cut-over areas. With blueberries in that list, this is a pest for us to be watchful for, and explains why it is also seen in New Jersey cranberries. [See also pages 32-33 of Cranberry Insects of the Northeast by A.L. Averill & M.M. Sylvia]

Spiny Looper - Phigalia titea (Cramer): The populations of this spanworm apparently cycle in forest stands, similar to other forest caterpillar pests, where it is typical to have several years of very low populations, followed by one or two years of extremely high populations that subsequently crash due to external factors such as viruses, fungi, lack of food, predators and parasitoids, etc. It was been reported on one Maine cranberry site in 2006, where numbers were quite high in distinct portions (patches) of the bed—highly characteristic of this spanworm—and left the infested area looking brown and burned. The larvae feed on the leaves of new growth. Some larvae nip the stem of new shoots, which then fall over. Its seasonal history has not been studied on cranberry. Over the last several years, though, it has become a significant problem for many Massachusetts growers so we may be learning more about this spanworm in the future. [See also pages 31-32 of Cranberry Insects of the Northeast by A.L. Averill & M.M. Sylvia]

Big cranberry spanworm - Eutrapela clemataria (J.E. Smith): Though only a few of these have been seen on Maine beds per season, they can be extremely destructive in small patches of a bed, resulting in fairly circular areas of damaged vines. They prefer to sever the flower buds and blossoms. Larvae appear in late June in Maine. They are dark brown with bumps across their back and grow to 2.5" in size. Spot-treating is usually the best approach if we should ever discover a problem with this particular spanworm.

Green Spanworm Itame sulphurea (Packard)	Chainspotted Geometer Cingilia catenaria (Drury)	Horned Spanworm Nematocampa resistaria
Found May 31st, 1999 in eastern Maine (and also in 2000 and 2001) (species not yet known)	Found June 1st, 1999 in eastern Maine (species not yet known)

If you have comments or questions about this page,
contact Charles Armstrong at: charlesa@umext.maine.edu

Putting knowledge to work with the people of Maine

Accessibility | Non-discrimination and Disability Resources | Non-disclosure | Contact
A Member of the University of Maine System
These pages are currently being maintained by the Pest Management Office, University of Maine Cooperative Extension. Page Last Modified: 05/15/08