UF/IFAS Okeechobee County Extension Service

458 Highway 98 North

Okeechobee, FL 34972-2578

Phone: (863) 763-6469

E- mail:  dfculbert@ifas.ufl.edu

April 6, 2006

Feature Article - for release the week of April 9, 2006

Dan Culbert - Extension Horticulture Agent

Don’t horse with the tents

While not a common critter found in this area, the Eastern Tent Caterpillar occasionally is found on some Florida trees.   They can thrive on several kinds of deciduous trees, but are especially fond of wild cherry, an infrequent weedy tree seen on roadsides and along pasture fencerows.

What is noticed is a clump of webbing in the tree limbs that is filled with masses of caterpillars.  In landscapes, this means that leaves will be eaten, and the area below the tree will be “rewarded” with lots of waste pellets from their hungry habits.  But that’s not all.

Recent research from UF/IFAS Animal scientists gives us another reason to be on the lookout for these critters: mares that eat these caterpillars may lose their foals. Information for this column comes from Extension Horse Specialist Dr. Saundra TenBroeck and Extension agents Mike Sweat and Rebecca Jordi.

The Eastern Tent Caterpillar

Eastern Tent caterpillars (Malacosoma amercanum) can be found in many deciduous trees, but they seem to prefer wild cherry, apple and crabapple.  Other trees know to support this featured creature include several Rose family relatives that are temperate fruit trees: cherry, peach, pear, and plum.  Other plants known to host tent caterpillars include the hawthorn, maple, oak, beech and poplar, especially if found growing next to the preferred host plants.

A Branch of Black Cherry, showing leaves and fruit.  Photo by: Kitty Kohout, Wisconsin State Herbarium

Adult moth of the Eastern Tent caterpillar, Malacosoma amercanum.  Photo: Mark Moran

Tent Caterpillars gain protection from theses masses of silk, but leave the "nest" to eat.  Photo: Robert L. Anderson, USDA Forest Service

Adult moths lay eggs in webs that are found in the crotch of tree limbs.  The eggs hatch in spring, and then begin their feeding frenzy.  These caterpillars do not feed within their webs, but congregate there during the night and in rainy weather.

The Eastern tent caterpillar larvae are covered with long, soft, light-brown hairs. There is a white stripe bordered with reddish brown down the back; along each side is a row of oval blue spots and brown-and yellow lines.

The caterpillars become fully grown - about 2" long - in four to six weeks. They feed in the trees and as they develop, they drop off.  As they crawl around on the ground, they can also chew up grass, clover and other vegetation.  They are known to travel as much as several hundred feet, crawling and feeding on the ground for about two days before climbing a tree or post and pupating.  

Each spins a white cocoon, and in about three weeks, it emerges as a light-reddish brown moth.  Adults seek a mate and continue their circle of life.  There is only one generation each year, with about nine months spent in the egg stage.

Caterpillars can be active for several weeks.  The specific month depends on geographic location.  March seems to be the month for Alachua County; north Florida counties will see caterpillars in April.  More northern states will experience these crawling critters at later times of the spring and early summer. 

Caterpillars may cause Abortions

The ground crawling phase of tent caterpillar’s development is the one that can pose a danger to horses which may inadvertently consume them.  It is believed that Mare Reproductive Loss Syndrome (MRLS) is caused by horses that eat Eastern Tent caterpillars.  Within 2 - 10 days of consuming the caterpillars, pregnant mares may abort, or their foals may be born weak and septic. (Note to horse owners and vets: other possible clinical signs may include uveitis, pericarditis, oral ulceration and laminitis.)

The University of Florida’s College of Veterinary Medicine has confirmed one case of MRLS and has two other suspect cases.  All occurred in Alachua County this spring, the first time this affliction has been reported in this state.  In 2002, Kentucky lost 1/3 of its foal crop, a loss valued at more than $300 million dollars.  Dana Zimmel, IFAS Extension Equine Veterinarian strongly recommends that all abortions and foal deaths occurring during periods of caterpillar activity should receive a post-mortem evaluation.

Managing Tent caterpillars

While tent caterpillars can nearly defoliate a tree when numerous, the tree will usually recover and put out a new crop of leaves. In the landscape, however, nests can become an eyesore, particularly when exposed by excessive defoliation. The silken nests are built in the crotches of limbs and can become quite large.  

Removal and destruction of the egg masses from ornamentals and fruit trees during winter greatly reduces the problem next spring. In the early spring, small tents can be removed and destroyed by hand. Larger tents may be pruned out and destroyed or removed by winding the nest upon the end of a stick. 

There are several pesticides that can be used against tent caterpillars depending upon the sites to be treated.  As always, the label is the law. The use of the bacterial-based “B.t.” (Bacillus thuringiensis) insecticides are encouraged, as they are less likely to cause injury to non-target organisms.   Be aware that some products that are labeled for one kind of site (e.g. around the home landscape) may not be labeled for use around livestock (e.g. horse pastures).

And beware of new cherry leaves

Members of the Apple and Cherry-tree family also have another black mark:  when the leaves are young they often contain a high concentration of certain toxins (glycosides) that when digested, produces a cyanide compound.  When livestock eat enough of this kind of foliage, the animal’s blood has a reduced ability to hold oxygen, which may lead to suffocation and death. There are other plants and other times of the year that can harbor this danger – check with your livestock professional or our office if you need more information.

Bottom Line: horse owners should remove any Wild Cherries from around their pastures, be on the lookout for these hairy caterpillars, be ready to move livestock from infested areas, and prepare to use labeled insecticides if the tent caterpillar crawls your way.  

I’ve placed more information on our Okeechobee web page, http://okeechobee.ifas.ufl.edu.  If you need additional information on Black Cherry trees and Tent Caterpillars, please email us at okeechobee@ifas.ufl.edu or call us at 863-763-6469.   Local residents can stop by our office at 458 Hwy 98 North in Okeechobee, and visit our Okeechobee County Master Gardeners from 1 to 5 PM on Tuesday afternoons.  

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Trade names, where used, are given for the purpose of providing specific information. They do not constitute an endorsement or guarantee of products named, nor does it imply criticism of products not named. The Florida Cooperative Extension Service - Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research, educational information, and other services to individuals and institutions that function without regard to race, color, sex, age, handicap, or national origin.  Florida Cooperative Extension Service / IFAS / University of Florida.  Larry A.  Arrington, Dean Last update: 04/06/2006 .  This page is maintained by Dan Culbert  

references

Eastern Tent Caterpillar, Malacosoma americanum (F.).  Taken from Insects and Diseases of Trees in the South. 1989. USDA Forest Service - Forest Health Protection. R8-PR16. 98 pp.  Athens, GA: University of Georgia, CAES, 9/2/04. http://www.forestpests.org/southern/easterntentcat.html 

Gilman, E and Watson, D. Black Cherry Prunus serotina (ST-516).  Gainesville:  Florida Cooperative Extension Service, 10/94. http://hort.ufl.edu/trees/PRUSERA.pdf 

Jordi, Rebecca. Questions (Tent Caterpillars).  Callahan, FL: Nassau County Extension Service, 3/10/06. http://nassau.ifas.ufl.edu/horticulture/questions/tentcat.htm 

Mare Reproductive Loss Syndrome (webpage).  Lexington: University of Kentucky, College of Agriculture, Dept. of Veterinary Science,  3/1/06.   http://www.ca.uky.edu/gluck/mrls/index.htm

Moran, Mark   Eastern Tent Caterpillar Moth.  webpage in: Study of Northern Virginia Ecology.  Fairfax, VA:  Stratford Landing Elementary School, 4/06 http://www.fcps.k12.va.us/StratfordLandingES/Ecology/mpages/eastern_tent_caterpillar_m.htm 

Sweat, Mike.  Eastern tent caterpillar, Malacosoma americanum. In: BAKER AG NOTES. Macclenny, FL:  Baker County Extension Service, April 2006, p.4 http://baker.ifas.ufl.edu/ag/agnotes/April%202006%20Ag%20Notes.pdf