They’re baaaack: Gypsy moths in King County to be sprayed by the WSDA

gypsy mothKing County is a welcoming community, but not for Lymantria dispar, more commonly known as the gypsy moth. These voracious moths are responsible for the defoliation of tens of millions of acres of deciduous and coniferous forests across the U.S. In Washington State, the Department of Agriculture (WSDA) carefully monitors for the presence of the gypsy moth, and this year has found both European and Asian gypsy moths in several locations, including Seattle and South King County.

WSDA is determined not to let the gypsy moth gain a foothold in our state, so when they find isolated populations, they eradicate them, typically using a substance called Bacillus thuringiensis kurstaki or Btk. Btk is a naturally occurring bacteria which experts believe is the safest and most effective eradication method for the gypsy moth. According to WSDA, numerous studies have shown Btk to be very low risk to human health. Btk impacts caterpillars alone and isn’t toxic to mammals, birds, fish, or other insects such as bees, lady beetles, spiders or ants.  Btk also doesn’t harm water supplies. Btk is certified for use in organic agriculture.

In recent years, control efforts in King County have included aerial and ground spraying in several Seattle neighborhoods, Tukwila, the Eastside and other areas of the county. This spring, a 130 acre area in Capitol Hill and a 640 acre area in Kent will be sprayed, along with other areas in Pierce and other western Washington counties.

Public Health agrees that the risk of Btk to human health is very slight. Despite widespread use, persons in the general population, children, and people with immune system disorders exposed to Btk through aerosol spraying have not been shown to experience infections. Health surveillance after spraying over large, populated areas has showed no increased use of health care for asthma, respiratory disease, or skin reactions and no worsening of asthma in children with moderate to severe asthma. A small number of persons have reported symptoms including skin rash, irritation of the eyes, nose and throat, and hay fever-like symptoms after exposure to Btk, though whether the people were impacted by Btk or other spray components is not known. To report an illness you think may be associated with gypsy moth spraying, call the Washington State Department of Health toll free at 1-877-485-7316.

As a general precaution, Public Health – Seattle & King County recommends all persons in spray areas minimize exposure to Btk. Persons who are more susceptible to infections or respiratory irritation should pay particular attention to minimize exposure. This includes people with an underlying illness such as leukemia, AIDS or other immune system deficiency, people receiving radiation or chemotherapy treatment, and people with asthma, emphysema or allergic sensitivities.

Residents in the spray area will be receiving postcards from WSDA regarding spraying plans and from Public Health – Seattle & King County with health information. Spraying usually takes place in the early mornings, and several sprayings are likely to be required. Learn more about past and present spraying, sign up to receive an alert when spraying is about to begin, and find contact information to WSDA at

For more information go to:

Public Health:

Washington State Department of Health:

Washington State Department of Agriculture (WSDA):

WSDA on Btk: