From the Seattle PI:

About 3 p.m. Sunday, Bellevue firefighters were called to the 17100 block of Northeast Fifth Street after neighbors saw flames and smoke. "It appears that a glass bowl, partially filled with water and elevated on a wire rack in a sunny area of the home's deck, provided the right conditions to focus the sunlight and start a fire," Lt. Eric Keenan said.

They should have listened to the warnings from the ants.