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Plant Industry - Plant Protection Section

Gypsy Moth Trapping Program

NCDA&CS has several different programs designed to detect and eradicate the gypsy moth.  Each year from mid-April to mid-June, roughly 18,000 traps are placed throughout the state.  These traps are monitored and removed between mid-July and mid-September, depending on weather and location.  The results from the statewide trapping effort are critical in determining the location of eradication treatments each year.

Traps are placed using a systematic grid system, with one trap every 2 kilometers (or 3 kilometers in the southern portion of the state).  This “base grid” gives us the ability to quickly detect infestations.

When a base grid trap catches several moths, a more detailed “intensive grid” is placed the following spring to determine if a population is reproducing and what its geographic extent is.  These intensive grids are usually one trap every 500 meters (0.5 kilometers); for very large areas, a density of one trap every 1 kilometer is used.

What are gypsy moth traps made out of?

A delta trap with several moths caught.
William A. Carothers, USDA Forest Service,

The majority of gypsy moth traps set by NCDA&CS are delta traps, which consist of wax-
covered cardboardhousing, a string, and an adhesive.  The string is saturated with the female sex pheromoneand is attractive to male gypsy moths, which have feathery antennae receptive to the pheromone. Once inside the trap, males are immobilized by the adhesive.

A smaller number of traps are milk carton traps, named for their resemblance to a waxy cardboard milk carton.  Milk carton traps are used in areas suspected of having a reproducing gypsy moth population because they can hold more male gypsy moths.  Milk carton traps also contain a pheromone string and a knock-down strip, which immobilizes the male gypsy moths.

Why is there a trap on my land?

A milk carton trap. William A. Carothers, USDA Forest Service,
Trap locations are predetermined prior to trap set.  This ensures that traps are not too close together or too farapart.  Often, traps cannot be placed at the exact predetermined location because of terrain or accessibility.  In any event, NCDA&CS personnel always make an effort to inform landowners when traps are set on their land.  If the landowner is unavailable, NCDA&CS personnel leave information about the trap.  Please click here for information that is distributed when a trap is set.

What if gypsy moths are caught in the trap?

Gypsy Moth
Photo courtesy of

It depends.  If only one or two moths are caught, and the surrounding traps had no moths, NCDA&CS will continue to trap the area at the “base grid” density, watching for the following years’ results.  However, if multiple moths are caught in one trap and the surrounding traps also had moths, NCDA&CS will place a more fine trapping grid (“intensive grid”) the following year to determine if there is a reproducing population. 

NCDA&CS, in cooperation with the Gypsy Moth Slow-the-Spread Foundation, Inc and the US Forest Service, uses a complex computer algorithm to determine potential problem areas based on the spatial pattern of gypsy moth trap catches from this year and previous years.  For more information on the Decision Algorithm, please visit the STS Decision Algorithm website. 


All treatment actions on state and private land are free of charge to the landowners.  For information on gypsy moth treatments, please click here


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NCDA&CS Plant Industry Division - Plant Protection Section
Plant Pest Administrator - Phillip L. Wilson
Physical Address: 216 West Jones Street, Raleigh NC 27603
Phone: 919) 707-3753 | FAX: (919) 733-1041