Singing insects are made up of Crickets, Katydids, Grasshoppers, and Cicadas. Each of these groups is further split into sections; for example, the Crickets are further divided into Field and Bush Crickets, Ground Crickets, Tree Crickets, Mole Crickets, and Trigs. Each of these sections is made up of numerous species. The Tree Crickets, which are up to about an inch long, are a particularly interesting group made up of two genera (Oecanthus and Neoxabea) in the United States and Canada. In the recording below, I am pretty sure that the long, melodious trill in the background (much like the song of the American Toad) is one or two species of Tree Cricket, while the louder "dee-did" is the characteristic call of the Common True Katydid (Pterophylla camellifolia). I've just started learning these insects, so if anyone disagrees with my assessments, please let me know. I apologize for the poor sound quality.
While some singing insects, such as Grasshoppers, call during the day, Tree Crickets call primarily in the evening and at night. Their purpose, as is the purpose in most cases of song in nature, is to attract a mate. Tree Crickets "sing" by holding their wings upright and rubbing together ridges on their forewings. Once a male has attracted a female and she approaches, the male begins to secrete a sweet liquid from the metanotal glands (also descriptively called "honey pots") on his back. The unsuspecting female climbs onto his back to eat this tasty treat, and as she is doing so, the male sneaks a spermatophore onto to the female. The longer she stays to consume this "love juice," the better chance there is that he will be successful in reproducing.
In the photo above, I have a Tree Cricket in the genus Oecanthus in the palm of my hand. Several of the species in this genus can be told apart from one another by the number and organization of black spots at the base of their antennae. By clicking on the photo to expand it, you can see black spots, but I can't tell for sure how many are present. Possibilities for this species include Snowy Tree Cricket (Oecanthus fultoni), Four-spotted Tree Cricket (Oecanthus quadripunctatus), Davis's Tree Cricket (Oecanthus exclamationis), and Narrow-winged Tree Cricket (Oecanthus niveus).
Above is a member of the other genus of Tree Cricket; this is a Two-spotted Tree Cricket (Neoxabea bipunctata), the largest tree cricket in North America. Two-spotted Tree Crickets are found throughout most of the eastern half of the United States. Be sure to click on the photo above to expand it for more detail.
I am just beginning to learn about singing insects, but I am quickly becoming obsessed with them. Much of the information in this post is from The Songs of Insects, a wonderful and beautiful book by Lang Elliot and Wil Hershberger that can also be found online at http://www.musicofnature.com/songsofinsects/index.html.
Now I just need to learn how to find and recognize more of these incredible creatures!