University of Florida Extension ServiceUF/IFAS Okeechobee County Extension Service

458 Highway 98 North

Okeechobee, FL 34972-2578

Phone: (863) 763-6469

E- mail:

October 4, 2007

Quick Links:  Hosts & Life History   Damage  Management  References

 Feature Article - for release the week of October 7, 2007

Dan Culbert – Okeechobee Extension Horticulture Agent

An Early Fall?  

Over the past few weeks our office has had several calls about caterpillars chewing up local oak trees.  It took us some time to find information about the culprit, but we were able to come up with a name of this seasonal pest – the Yellow-necked caterpillar.

Unfortunately, once the damage is noted, it is often too late to do anything about it.  But there are some approaches that can help keep this “weasely worm” from being such a problem next year.  

A few years ago, our area had an infestation of another oak-eating caterpillar.  These critters were gray and pink in color, and are called the Pinkstriped oakworm. The caterpillar discussed today is a different species, Datana ministra.  It is not nearly as big, and when mature, is black with yellow stripes and a yellow ring around its neck.


Adult Yellowneck Caterpillar Moth.  Photo: Bob Patterson, Mississippi State University.


Pupa of Adult Yellowneck Caterpillar. Photo: Lacy L. Hyche, Auburn University


Egg mass on underside of leaf. Photo: Lacy L. Hyche, Auburn University


Young stage Yellowneck caterpillars. Photo: Univ. of Illinois


Typical red-yellow color phase of mid-stage yellownecked larvae showing defensive behavior pattern. Photo: Lacy L. Hyche, Auburn University

yellownecked caterpillar, Datana ministra  (Lepidoptera: Notodontidae)  

Full sized yellownecked caterpillar.  Photo: Gerald J. Lenhard



Hosts and History The Yellowneck caterpillar occurs throughout much of the US, but is more common east of the Rocky Mountains.  Oaks and hickories including the Pecan are common meals for this insect.  Other hardwood hosts in our area might include Elms, Maples and the River Birch. The insect will spend the winter and spring as a pupa in the soil. These shiny dark brown objects are about an inch long and ¼ inch around.  Adult moths begin to emerge in July.  Moths are tan to reddish brown, with four narrow dark lines across each front wing.  The edges of the wings are scalloped.  Their back wings are hidden at rest but will be yellowish-brown and 1½ inch wide. Female moths lay egg clusters of 50-300 on the lower surface of leaves.  Small larvae usually begin to appear in late July or early August.  The larvae feed together in colonies during summer and fall.

Newly hatched larvae have black heads. The young caterpillars are mostly red with patches of yellow on the back and alternating yellow or white lines along the sides. These early stage larvae rip off the lower surface of the leaf.  Skeletonized leaves turn brown, so small clumps of dead leaves canopy are early signs of caterpillar feeding.  

As they mature, entire leaves are consumed, leaving only a nub of the petiole.  By the time tree damage is noticed, the larger caterpillars will now have a black head with a bright orange to yellow collar or neck – this gives the insect its common name.  Yellow-necked caterpillars have a black body with 8 thin yellow to white stripes.  They are also identified by their sparse, long white or gray hairs. When they reach full size of almost 2 inches, they drop to the ground to pupate in the soil.  In other areas several generations per year may occur, but in Florida there is only one generation per year. Importance Colonies of caterpillars of different ages may be found through August into mid-October.  During development, larvae leave the foliage periodically and congregate on branches to rest and molt.  They travel and eat in groups of thirty to a hundred for protection.  When a possible predator (birds & other insects) disturbs these caterpillar colonies, they assume a characteristic U-shaped alarm position: the head and rear end are raised.   On large trees with ample foliage, only a few branches may be stripped by the time larvae reach full size. However, small trees with fewer leaves can be completely consumed by a single colony. Several consecutive years of severe defoliation will stress trees.  The health of a tree may deteriorate if other stress factors also occur, like drought, hurricanes, construction damage, and the like.  Landscape trees are more often bothered by these insects than hardwoods found in a forest setting.

Besides the loss of tree foliage, homeowners report that falling frass (dark pellets of caterpillar excrement) is a problem on sidewalks and patios.  Typically, feeding colonies defoliate one branch then move to another. 

>Management Predators, parasites, disease, and unfavorable weather usually keep caterpillar populations low.  Outbreaks are rare, and the factors that cause occasional outbreaks are not known.  Promote tree vigor and health to aid in the recovery from defoliation. Use an approved insecticide for high-value trees or extremely damaging moth populations. Because this insect feeds in groups, early feeding may controlled by pruning off infested branches by pulling off the caterpillars by hand.  This caterpillar is most numerous in late summer when its feeding causes little permanent damage to the tree.  There is also evidence that predator wasps may help keep populations of these caterpillars down.  In these cases, no control is necessary. Healthy trees usually survive and recover; however, defoliation can cause dieback of branches and twigs, loss of growth, or even tree mortality, if defoliation continues through several consecutive years. Early detection of the small caterpillars is a key management step that reduces the need for pesticides.  Bacterial and chemical insecticides are most effective if applied when the larvae are small.  The use of the least-toxic insecticide Bacillus thuringiensis k. is a possible choice for home landscape use.  Homeowner use of chemical insecticides on fully mature caterpillars will not be effective, and may kill predators that help to keep the numbers low.

Licensed Commercial landscape applicators that have access to power sprayers may wish to use a number of registered pesticides if the situation requires it.  Please check with the latest UF/IFAS recommendations, and follow ALL label directions.

I’ve placed more information on our Okeechobee web page,  If you need additional information on oak tree caterpillars, please email us at 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 3 PM on Tuesday afternoons.  GO GATORS!


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Barnard, Edward L. and Dixon, Wayne N.   Yellownecked Caterpillar – Insect of Hardwood Foliage (Bulletin No. 196-A)  Tallahassee: FDACS/Division of Forestry , October, 1983.

Culbert, Daniel F.   "What’s Chewing my Oak Tree?"  Okeechobee: UF/IFAS Florida Cooperative Extension Service, 9/21/05.

Hyche, Lacy L.  Yellownecked Caterpillar  Datana ministra.  Auburn: Auburn University Department of Entomology & Plant Pathology 4/2002.

Yiesla, Sharon. et. Al.   Yellownecked Caterpillar Datana ministra.   Urbana-Champaign: University of Illinois Selecting Trees for your Home Extension Service website, 2007.