Watch For Buck Moth Caterpillars Now

Daniel Gill, Merrill, Thomas A.  |  4/19/2005 10:28:56 PM

Get It Growing

Get It Growing News For 03/19/04

By Dan Gill
LSU AgCenter Horticulturist

The buck moth caterpillar can be found feeding on trees in spring, particularly oaks such as live oak and water oak. Populations vary around the state from year to year, and this is an excellent time to start watching your oak trees for signs of infestation – particularly if you had a problem with these pests last year.

The large, black-spined caterpillars that come out in the spring actually begin their life cycle in late November through December. At that time, the adult buck moths, which have black and white wings and rusty red abdomens, appear from underground where they spent the summer in the pupal or resting stage. Once they emerge, the male and female moths mate, and the females lay clusters of 80 to 100 eggs on small twigs in the canopies of oak trees.

The eggs generally begin to hatch from mid- to late-February through early March. As the feeding caterpillars grow and develop, they shed their skin several times. When this occurs, some of them lose their hold on the branches and fall to the ground. If they are not finished feeding, they will try to climb back up into the tree. This has led to the mistaken idea that these caterpillars originate in the ground and crawl up into trees.

Six to eight weeks after hatching (in April or early May), the spiny caterpillars grow to about 3 inches and have finished feeding. Masses or groups of the caterpillars (individuals in a group are siblings hatched out of the same egg cluster) begin to move down the trunk of the tree and look for a place to pupate in the ground. Once on the ground the group spreads out.

When the caterpillars wander around on lawns, sidewalks and porches – where you or your children may come into contact with them – a situation exists that can lead to problems.

The buck moth caterpillar produces a painful, burning sting when its spines are touched. The irritation is caused by fluid released from the caterpillar’s spines, which puncture the skin and let the irritating venom enter. The result is a swollen, red, burning area.

A caterpillar sting can be very serious to those individuals who are allergic to insect venom. Those who are highly allergic to insect bites or stings should seek immediate medical attention if stung by a caterpillar.

For most of us, however, the sting is painful, and the area will stay tender for several days, but it is not a serious health threat.

Buck moth caterpillars also can pose a health risk to the trees they feed on. Heavy feeding of caterpillars can strip most of the foliage from a tree – forcing it to grow a new set of leaves. Although not life-threatening, this can weaken a tree if it happens several years in a row. Any tree that is stripped of its foliage should be sprayed to control the caterpillars the next year. Trees that receive only a moderate amount of damage each year are not seriously affected.

This pest is most vulnerable to control when in the caterpillar stage. There is no practical way to kill the adults or pupa. Since the caterpillars hatch from eggs already in the canopy of the tree, the only way to kill them is to spray the tree.

To check on the current population in your tree, use binoculars to look for the black masses of caterpillars on the outer twigs and branches of the tree this month. If you see a number of clusters, consider having your tree sprayed.

It is far better to spray the tree, or have it sprayed, before the large caterpillars begin to migrate to the ground. Generally, spray applications made in mid-March allow time for all of the eggs to hatch but kill the caterpillars while they are small and still in the tree.

A relatively non-toxic pesticide that may be used on early stage caterpillars is Bt (Bacillus thuringiensis). This bacteria attacks only caterpillars and is harmless to wildlife and people (but do keep it away from your butterfly gardens). Acephate is another pesticide that can be used by home gardeners.

Older oak trees generally are too large for home gardeners to spray effectively with the equipment they have, so a professional company must be hired to do the job. Some companies will spray your tree with Bt if requested, but remember it must be done while the caterpillars are young and actively feeding.

It does little good to spray one tree if others nearby are infested, so you may want to talk to your immediate neighbors about a coordinated effort. You often will find that a company will be able to give you a better price per tree when several trees in a block are sprayed at one time.

If not killed while they are in the tree, the caterpillars eventually will begin to migrate down the trunk. When you see a mass of caterpillars on the trunk where you can reach them, take an old shoe and smash them – being careful not to come into contact with them. It’s not a pleasant job, but it’s fast-acting, extremely effective and environmentally friendly, and it keeps the caterpillars from reaching the ground.

If you are dealing with the caterpillars on the ground, sidewalks and porches or crawling up the sides of buildings, sweep or rake them into a dust pan and dump them into a bag. Place the bag on the ground, step on it thoroughly and throw it away. This gets the caterpillars away from people far faster than spraying and reduces the use of pesticides.

Once again, be careful not to touch the caterpillars in the process. I generally wear gloves. But I also keep in mind that ideally it is far better to have your tree sprayed before the caterpillars.

Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at A wide range of publications and a variety of other resources are available.


Contact:  Dan Gill at (225) 578-2222 or
Editor:     Tom Merrill at (225) 578-2263 or

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