They are information weapons against a tree pest.
According to the USDA and Vermont's Ag department,
The purple traps are coated with an adhesive that captures the insects when they
land and are baited with a lure to attract the pest if it is present. In
addition, the color is thought to be attractive to EAB, and is relatively easy
for humans to spot among the foliage.
What's the enemy?
[The]emerald ash borer (EAB), a non-native, wood-boring beetle that has
killed tens of millions of ash trees in the eastern United States and Canada.
Good news: "To date, EAB has not been detected in Vermont."
For more information, check out this site.
Or read this:
“The traps being placed around Vermont will help us discover if we have EAB
in Vermont early on which allows us to address this invasive pest immediately,”
said Jon Turmel Vermont State Entomologist. “Early detection is the best tool we
have to fight EAB...
The triangular purple traps do not pose a risk to humans, pets, or wildlife;
however, the non-toxic glue can be extremely sticky,” said USDA State Plant
Health Director, Mark Michaelis. “We want people to understand that the traps
don’t attract or pull beetles into an area, but rather they are a detection tool
to help find EAB if it is present in the area.”
These traps will be
monitored and remain in place throughout the summer during the beetles’ flight
season. The traps will be monitored throughout the summer and removed in the
fall. Results from the trapping will be available once the traps are removed.
If you see a purple trap on the ground, please call the USDA’s toll-free
num ber: 1-866-322-4512. The EAB hotline is staffed during regular business
hours and a message may be left at any time. Callers are asked to include a name
and telephone number.
(thanks to Warren King; image from takomabibelot)