US: As in Alfred Hitchcock's film The Birds, the first signs of something strange and disconcerting about to happen in nature are barely noticeable - a dog snapping wildly at the air, a funny buzzing sound in the evening.
But people in Washington and other US cities know what it means and what is coming. An invasion of billions of locust-like insects is under way. For the next few weeks, outdoor concerts will be cancelled, wedding receptions kept inside and barbecues confined to garages as clouds of cicadas take over the suburbs.
It only happens every 17 years and this time it may amount to the "largest insect emergence on earth", according to Prof Keith Clay, a cicada expert at Indiana University.
The thumb-size insects with black bodies, yellow legs and translucent wings slumber underground for 17 years and then emerge for a three-week frenzy of mating before laying eggs and dying. The insects make a loud sizzling noise as they mate in trees, a din that can drive people crazy, but they are relatively harmless to humans.
They don't bite, nor do they strip away vegetation, as locusts do.
The insects "started emerging from the ground by billions" in Bloomington, Indiana, on Monday, Prof Clay told a news conference.
The highest density will be in Ohio, Indiana and Kentucky, but they will bring their cacophony as far north as Pennsylvania and New York.
The periodical cicada, known as magicada, is found nowhere else in the world. It is highly synchronised, coming out by the billion at the same time to lay eggs in tree branches, from which the larvae drop to the ground and burrow deep to feed on tree roots for another 17 years.
Why they have a 17-year life cycle is a mystery to scientists, who say their like will not be seen again until 2021.