Cicadas

They are called periodical cicadas. They only come up from the ground once every 13 years and sing in trees. Thats their mating. they will be around long enough to lay their eggs in tree branches then they will die and the eggs will fall to the ground and burrow down, about 30 days. And wait 13 more years.  They don't sing at night, they only sing during the day. Sounds like alien space ships. I copied and pasted some info:

There are many interesting aspects of a periodical cicada emergence, including the length of time they spend underground, their massive numbers, their visual appearance, their amazing songs, and the variety of reactions people have to the cicadas. One of most amazing things you can witness during a cicada emergence is to watch cicadas emerge from the earth as nymphs, crawl up a tree, shed their skins, spread their wings and become adults.

Step 1: The nymph grabs hold of a leaf

Periodical cicadas will typically emerge over a period of several days. If you discover that cicadas have emerged in your yard by finding their skins (exuvia) or adult cicadas, chances are good more cicadas will emerge later that night.
Nymphs will crawl around until they find a place to grab hold of with their tiny tarsal claws. Usually they find part of a tree branch or leaf. Sometimes they find a car tire, a brick wall or a barbecue.
Step 2: The back of the cicada splits open, and the cicada pushes itself out.
The skin of the nymph splits open along the middle of its back, all the way up to its head. The cicada then pushes itself out back-first. You’ll notice that the cicada is white in color with two black spots on its back. At this point the cicada’s body is very soft — until a cicada’s body has hardened, we call them teneral, which means soft or tender in Latin.
Step 3: With its abdomen anchored in the nymph skin, the cicada curls back, freeing its legs and spiracles.
The spiracles are the holes through which the cicada breathes. You’ll notice fine white strands connected to the nymph skin — those were once connected to the spiracles.
Step 4: The cicada curls forward, grabs hold of its former skin, and frees its abdomen
step 5: The cicada crawls away from its old skin and prepares inflate its wings
Step 6: The cicadas wings fill with fluid and expand
The cicada inflates its wings using haemolymph, a blood-like fluid also used to transport nutrients in a cicada’s body.
Step 7: The color of the cicada darkens and its body hardens
Once the cicada has expanded its wings, the cicadas will turn their final color and their bodies and wings will harden. Once the body and wings are sufficiently hardened, they are able to fly and sing.