Wednesday, August 29, 2012

Riverside Ramble

  A river runs through our Pennsylvania mountains.  A lovely river... the West Branch of the Susquehanna River.  The banks of the river are fun to explore.  Won't you join me on a late-summer riverside ramble?
The riverine setting, along with the unique flora and fauna of the riparian habitat, provides a great place to ramble.  There is so much to see!

I especially enjoy the community flourishing on the shoreline and the low terraces which are periodically exposed during times of low water.
 With a cursory glance, the river bank looks scruffy and overgrown, but personally I think it has a beauty all it's own... rivaling a garden.
   Let's take a look at the plants in this fantastic riverside garden.  My favorite is the Purple Aster... lookin' good there in the foreground (photo above) against the muted lavender of the Joe-pye Weed, the white of the Boneset and the yellow of the Sneezeweed.
Yup, Sneezeweed.
The brilliant red of the Cardinal flower is also there in the mix. 
Cardinal Flowers attract many hummingbirds and swallowtail butterflies.  Here is a photo of a Spicebush Swallowtail as it flutters on a Cardinal Flower. 
Here an Orange Sulfur Butterfly is nectaring on this Boneset.
   The floodplain is bustling with butterflies, beetles, and other buzzing beings.  This insect horde seems to find the riverside garden very attractive, but not all streamside plants benefit these insects.  Some plants "eat" them.  The minute, carnivorous Round-leaf Sundews grow between the stones in the more open areas.  The sundew's leaves are covered with stalked beads of glue which act like flypaper and ensnare insects that make contact.  Upon catching an insect the "tentacles" encircle the insect and digest it.
The Round-leaf Sundews add to the garden's beauty and intrigue with their sparkling jewels of sticky glue.
   Other members of this riverside community are bushes and birches and rushes.
There are sedges and grasses... like this Yellow-eyed Grass.
 Wow! all this... and we've only gone a stone's throw, from the yard to the water's edge.  There's much more thriving on the gravel bars up and down the river.
O boy, don't get me started... it's a long, crooked river.

Saturday, August 25, 2012

An Extraordinary Cricket Song, Part II

   Tree cricket songs add to the pleasant night sounds during these summer evenings.  Additionally, tree cricket songsters put on a surprising performance if a person has the opportunity to observe them singing.
tree cricket song amplified by hole in leaf
   At dusk, and on into the night, we've been hearing some plaintive tree cricket songs emanating from our fence row.  The source of those melancholy, intermittent trills are Narrow-winged Tree Crickets.  Their song is a medium pitched trill of a few seconds duration followed by a short pause.  With some careful searching I found numerous tree crickets in the trees... singing from between the leaves of our young Walnut trees.
tree cricket singing through hole in leaf
   Tree crickets raise their wings almost perpendicular to their body while singing. Their sounds are produced by rubbing one forewing aginst the other. One wing has a file and the other has a scraper. As these pass over each other they cause the wings to buckle (vibrate) and produce the sound pulse. 
  Most of the cricket photos I have are of singing crickets, but here is a picture of a Narrow-winged Tree Cricket (Oecanthus niveus) at rest.  Here is a link to a website with some information about crickets and a recording of a calling Narrow-winged Tree Cricket and here is another tree cricket website.
 As I mentioned, in our backyard, the tree crickets sing from between the walnut leaves.  I meant that literally.
The Narrow-winged tree crickets seem to prefer singing with their wings aligned in the gap between the edges of two leaves.
This unusual position is no accident.  The crickets are using the leaves to amplify their songs.  
Leaves amplifying a tree cricket song
This is accomplished by using the leaves as an acoustical baffle. As the cricket's wings vibrate they produce sound waves off the front and the backsides of the wings (dipole sound source).  The leaf baffle helps prevent the front sound waves from interfering with the back waves (destructive interference) which avoids cancellation of some of the precious volume of sound these small creatures can produce.
   These little acoustical engineers, the tree crickets, also like to sing through a hole in a leaf.
one secret to a tree cricket song
I suspect the Narrow-winged Tree Cricket is an opportunist... making use of any suitable and properly sized hole that some other creature made.
However, there are some species of tree crickets that chew their own holes which they use as amplifiers.        Most of the time the Narrow-winged Tree Crickets that I have observed just avail themselves to any convenient and suitably sized gap in the leaves.
   The many leaflets on the walnut trees provide exactly what the crickets need for their sound system. Perhaps for that reason,  I have found few tree crickets on the other trees and bushes in our fencerow. Another possibility is the fact that the walnut's low branches overhang the driveway where I can conveniently observe the tree cricket's nightly performances.
I did find a tree cricket singing through the "v" at the base a grape leaf.
Notice the contortions the tree cricket puts itself through while calling... in order to position itself the most advantageously with its chosen sound baffle.
   Those efforts are especially noticeable when the tree cricket uses the edge of a single leaf for its acoustical effect.
   I can hear the tree crickets songs way out across the yard, but when close at hand they can be difficult to hear.  I believe this is because of the directional nature of their "sound system".
   Ordinarily, the various night sounds of the katydids and crickets all blend into a pleasant din that one simply ignores.  However, when one picks out a distinctive call and ponders what extraordinary efforts the songster employed to broadcast that song out into the night...
... each cricket call is an extraordinary song. 
  Those songs are calls for mates, but they call me as well.  A cricket's song calls me to search for the singer in hopes of witnessing an outstanding performance of acoustical ingenuity. 
I think knowing the crickets and their trills is a thrill.

Monday, August 20, 2012

An Extraordinary Cricket Song

Our cat apparently thinks that listening to crickets sing is worthy backyard entertainment.
 Not only was Kitty listening to the cricket's song, but he was also watching the cricket as it sang from the crack between the stones.
I too, have watched crickets sing... and I'm impressed with their sound production techniques.  Field crickets, like Kitty was intently watching, have different methods of projecting their sounds than the elusive tree crickets I've been chasing with my camera.  Both kinds of crickets have impressive means of singing out for mates.
   I've recently been taking photos of crickets singing... like this tree cricket in the picture below.  The photo illustrates the remarkable things tree crickets do as they sing.  My next post will focus on tree cricket songs.
   On summer days and evenings when the air is filled with cricket sounds, I like to ponder the acoustical engineering feats of the various crickets.  I like to know "the how" of each cricket sound... then each cricket song becomes extraordinary.
An Extraordinary Cricket song, Part II

Saturday, August 18, 2012

Catalpa Springs

   We have a Catalpa tree growing on the riverbank in our front yard.  We enjoy the Catalpa's giant, heart-shaped leaves and, at times, the leaves' nectar "springs" make for great conversation.
Even the bees love Catalpa leaves... at least this time of year.
extrafloral nectaries on catalpa leaves
  Bees, yellowjackets, wasps, and ants are attracted to the Catalpa leaves because the leaves have extrafloral nectaries which produce nectar on the underside of the leaves.
The extrafloral nectaries are located where the leaf veins meet the midrib.
Extrafloral nectaries on a Catalpa leaf
The extrafloral nectaries are also located at the base of the leaf where the leafstalk branches out.
I like to think of these spots that seep nectar as "springs".

   The Catalpa's nectaries do a good job of attracting a variety of insects. The plan is to provide an attractant for the wasps, bees, etc... and in return, gain some protection against herbivores. In other words, providing "refreshments" for all these predators increases the chances of them finding caterpillars, or other pests on the Catalpa leaves... and with all these hunters milling around, it's more likely the pests will be killed or parasitized.  
 Yellowjackets are the most common visitor to our Catalpa.  We've all seen yellowjackets foraging at a picnic for anything... even grilled chicken.  Yellowjackets love meat... here is a photo of some yellowjackets feeding on a "grilled" dragonfly on my vehicle's grill.
 It follows, that, if there are plenty of these meat-hunting wasps visiting the leaves of the Catalpas, there will be increased chances of them capturing any leaf-munching caterpillars.
    Yellowjackets aren't the only visitors to the Catalpa's nectaries.  I've seen plenty of other kinds of visitors... like this iridescent bee.
I saw numerous ants on the Catalpa leaves.
A number of solitary wasps came to the "sweet spots".
I noticed a Lady Beetle scurrying up the midrib... from one nectar seep to another.
   From the looks of the picture below, even spiders may try to take advantage of the visitor-attracting nectar springs by lying wait nearby... just like they do on flowers
   The way I see it... it's astounding to see the Catalpa tree pit the wasps against the caterpillars.

Sometimes, our backyard entertainment is our Catalpa tree.

Monday, August 13, 2012

An Unfortunate Butterfly

We usually see butterflies flitting around the yard.  It's not every day we see one dangling lifelessly below a flower.
 This Cabbage White Butterfly fell prey to a crab spider that had been waiting in ambush on a burdock flower.
 I didn't have to look far to find another crab spider ready to ambush some unsuspecting insect as it visited the burdock's flowers.
 Crab spiders commonly hide in flowers... ready to ambush insects that visit. They simply wait for a meal to be attracted to the flower's nectar or pollen.
 In some flowers the spiders are even more concealed and camouflaged than on this burdock.
The strategy of letting the flower do the advertising seems to be a rather successful one...
... but for the butterfly, that means every flower visit holds some danger.