Get It Growing: Watch For Buck Moth Caterpillars During Spring

Daniel Gill, Merrill, Thomas A.  |  2/27/2007 4:03:09 AM

Get It Growing News For 03/16/07

By Dan Gill
LSU AgCenter Horticulturist

The buck moth caterpillar can be found feeding on trees in spring – particularly oaks such as the live oak and water oak. Populations vary around the state from year to year, but this is an excellent time to start checking your oak trees for signs of infestation.

Checking is especially important if you had a problem with them last year.

These large, black-spined caterpillars that occur in the spring actually began 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, emerged from underground, where they spent the summer in the pupal or resting stage. Once they emerged the male and female moths mated, and the females laid clusters of 80 to 100 eggs on small twigs in the canopy of oak trees.

The eggs begin to hatch generally from mid- to late February to early March. As the feeding caterpillars grow and develop, they shed their skin several times. When shedding 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 climbing has led to the mistaken idea that these caterpillars originate on the ground and crawl up into trees.

By 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. 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. A caterpillar sting can be very serious to individuals allergic to insect venom. Those who are highly allergic to insect bites or stings should seek immediate medical attention if stung by a caterpillar. But for most of us, although the sting is painful, and the area will stay tender for several days, it is not a serious health threat.

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, leaf loss 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 only receive a moderate amount of damage each year are not seriously affected.

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

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

A couple of relatively nontoxic pesticides may be used on early stage caterpillars. Bt (Bacillus thuringiensis) attacks only caterpillars and is harmless to wildlife and people (but do keep it away from your butterfly gardens). Spinosad is another good choice.

Pyrethroids (such as bifenthrin, permethrin, cyfluthrin in various brand names) also can be used by home gardeners to control this caterpillar and are recommended if spraying is done late in the season.

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 spraying 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.

When you see a mass of caterpillars on the trunk – where you can reach them – take an old shoe and smash them. Just be careful not to come into contact with them. It’s not a pleasant job, but it’s fast-acting, extremely effective and environmentally friendly. Best of all, it keeps the caterpillars from reaching the ground, where they can start another cycle.

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.

Ideally, however, it is far better to have your tree sprayed before these pests come down to ground level. 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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