1. Gypsy moth populations cycle up and down dramatically even without treatment. In bad years the caterpillars are ubiquitous and offensive; they can even make a mess underfoot. But no known treatment, including Btk (a variety of Bt), eradicates them. Unfortunately, they'll be back.
2. Gypsy moth caterpillars attack many kinds of trees but are especially fond of oaks. In a bad year they can defoliate large expanses of forest. Fortunately a single defoliation does not kill a healthy tree; it will most likely re-foliate right away.
   
3. Aerial spraying an urban neighborhood is neither a cost-effective nor equitable use of taxpayer money nor, as mentioned above, will it eradicate the moths. But homeowners can take many actions on their own to control gypsy moths on their property. (Here's an older but thorough reference.)
4. Btk is non-specific. It kills "good" and "bad" caterpillars indiscriminately. Moreover any kind of spray can trigger allergic or asthmatic reactions in sensitive children or adults.

Homeowners should weigh the pros and cons of aerial Btk spraying. You can start with these contrasting articles, one biased against Btk, and one biased for Btk.

Brief FAQ ("Frequently Asked Questions") about spraying in Madison

How do I know if I am in a Btk spray zone?
The city mailed you a letter if you are in a spray zone for 2009. You can also find all Dane County spray zones here.

How do I opt out of being sprayed?
You must inform the City Forester in writing (email will do, but a phone call will not). Be aware that the City Forester and her staff generally make an effort to dissuade homeowners from opting out.

When must I elect to opt out of being sprayed?
The deadline for opting out in 2009 has passed. It was 3:00pm on February 20, 2009.

When will Btk spraying occur in 2009?
Spraying of the Regent Neighborhood, Shorewood and Hoyt Park spray zones occurred early in the morning on Thursday 21 May 2009. If you are in or near a spray zone, watch or listen for small yellow planes, flying low and early. (You can subscribe to email updates on the spray schedule here.)

Where can I get more information about the spray program?
Detailed information on the program is available at the Wisconsin DNR website. This includes maps of all spray zones in Wisconsin and email and telephone contacts.

How much city tax money goes to the Btk spray program?
The city of Madison allocated about $29,000 in 2008 and again in 2009 for Btk spraying.