Friday, May 29, 2015

Aquatic Life Dazzles in May‏

Mink on rock in Chesnut Creek
For me wetlands have always been very special places.  I am not quite sure why that is although we all have our favorite habitats.  I spent a lot of time while young roaming along a creek in GA and these memories have stayed with me until now.  The animals of aquatic habitats are generally more limited in their distribution than terrestrial species and show many special adaptations in life cycles.  

Twelve spotted skimmer
Dragonflies are very primitive insects and highly predaceous both as aquatic larvae and adults.  Despite their ability to migrate long distances as adults, they are required to find wetlands to breed.  Two distinctive odonates in our farm ponds are the male twelve spotted skimmer and blue dasher, both of which are more colorful than the females.  

Blue dasher dragonfly
Males set up territories along the shorelines and await the arrival of females.  The aquatic larvae subsequently emerge and metamorphose into the radically different adults.  Such a metamorphic life style allows the adults and young to avoid competition for food.  But it is a difficult process fraught with danger.  
I found a dragonhunter soon after it emerged from the larval skin and it was bright green!  This tiny T Rex of dragonflies eats other odonates.  The green color is quite unusual and is thought to be the color of the copper based blood pigment, hemocyanin, showing through the transparent cuticle of the still developing body and wings.

This time of year there are quite a few dark insects with white markings flying near the New River that are a strange type of critter called a fishfly (Nigronia) related to the dobsonflies. They have an aquatic nymph, the hellgrammite, familiar to fishermen as a good bait and for their ability to bite hard!  This aquatic predator may live for three years before emerging as an adult which lives only a short time, during which it mates and lays eggs.  

Female bullfrog
A very obvious aquatic amphibian predator is the bullfrog, well known for its loud call and willingness to eat anything that will fit into its mouth.  This is a female, which is obvious from the small size of the ear drum (about the diameter of the eye).   Males have larger ear drums, the better to hear their male competitors for territories and females.   Bullfrogs remain near ponds and their tadpoles mature in water, but there is little competition between the life stages since the young are mainly herbivorous.  

Rainbow trout
An aquatic predator that likely eats tadpoles is the rainbow trout, which is an introduced or exotic species in the east since it originated in the western US.   It is widely planted in streams because of its status as a game species, despite the damage it does to native stream ecology.  This includes competition with the native brook trout.  It is interesting how differently managers view trout compared to exotic species of plants which are often ruthlessly exterminated.  

Northern water snake
An aquatic snake that eats fish and amphibians is the northern water snake, a very wide spread generalist. The queen snake that can occur in the same streams has a very different diet specializing on recently shed crayfish.  This type of extreme limitation in diet is quite remarkable and raises the question of why this would happen.  Apparently a specialist can become so efficient at feeding on one group of prey that are not eaten by other snakes that it occupies an alternative niche and thus avoids competition.  

Queen snake
The queen snake has also become even more aquatic than other fresh water snakes- I found that its skin is more permeable to water and likely also to oxygen than any other snakes, including sea snakes.  So it is a most unusual species despite its normal external appearance.

A top predator in our streams and lakes is a large weasel, the mink.  They are semi-aquatic, foraging in water and on land nearby.  They are quite ferocious and will kill prey even larger than themselves.  Our neighbors tell stories of their attacks on chickens.  I see them in our yard often but their lives are shrouded in mystery for the most part.

So enjoy the remarkable fresh water species in our lakes, ponds, streams and rivers.  Their lives are fascinating and reveal the extreme variation in life cycles which can occur as species adapt to exploit the environment and minimize competition and predation.

Bill Dunson 
Galax, VA and Englewood, FL 

Wednesday, May 27, 2015

Butterfly Beauty and a Beastly Habit‏

I recently was walking along the edge of a local river and encountered the inevitable goose poop along the shore.  While humans may go YUCK when they see animal dung, our beautiful butterflies go YUM !  An all vegetable diet is often low in essential salts such as sodium, which is rich in animal excrement.  So butterflies such as these tiger swallowtails commonly "puddle" on dung and sip up the salts which they need.  So if you are looking for butterflies, follow a horse!

Bill Dunson

Do butterflies sunbathe?‏

Red admiral sunbathing on New River Trail

The red admiral is a beautiful butterfly with a very wide distribution around the world.  It appears to be able to move northward rapidly in spring and deal with cold mornings.  It was 48 F on our back porch this morning in VA and I saw this red admiral apparently sunbathing on the New River Trail at mid morning.  It held its wings partially open so that sun and heat would reflect down on its dark body.  This allows it to raise its body temperature and fly earlier than it would otherwise be able to do.

Bill Dunson
Galax, VA

Sunday, May 24, 2015

Springtime Odes and Leps‏

Carolina saddlebags
As springtime temperatures wax and wane, insect life begins to increase and we are treated to the gradual re-awakening of an insect horde.  Two of my favorite groups of insects, the dragonflies (odonates or "odes" for short) and the butterflies (lepidopterans or "leps" for short) provide a lot of excitement during this early time of year.  It is very rewarding to see old friends from these insect groups reappear and colonize their habitats.  

One of the most easily recognizable of the dragonflies this time of year is the Carolina saddlebags.  The large dark reddish patches at the bases of the hind wings and the red abdomen of the male are very distinctive.  The purpose of these markings is not obvious and they would seem to make the insect a target for predators.  But this is a very agile flyer which is not easy to catch.  

Lancet clubtail dragonfly
A nearby dragonfly, the lancet clubtail, is very drab and less noticeable.  In fact this well camouflaged species is often found perched on the ground or low vegetation.  These are both very aggressive predators on insects as adults and as aquatic nymphs.

Red admiral butterfly on fringed phacelia
One of the most beautiful butterflies is the red admiral.  It is migratory and found also in Africa, Eurasia and Central America. The purpose of the bright colors of the inside of the wings is not clear since the caterpillars feed on nettles and are not likely to be toxic to predators.  Since the butterfly is an erratic and rapid flyer, perhaps these are simply flash colors involved in species recognition.

Light blue azure
A common butterfly in May is the light blue azure, which is one of several members of the spring/summer azure complex.  The difficulty of separating these azures reminds us that evolution continues to occur even now and the distinctions we try to make between individual species are not always clear in the real world.  

Female white morph orange sulphur
Another confusing group is the sulphurs.  The individual shown
is probably a white morph orange sulphur, but the distinction between it and the clouded can be difficult in the field. To add additional confusion a third identification challenge was flying in the same area, the duskywing skipper. This appears to be a Juvenal's duskywing that is nectaring on a geranium flower.  They are as dark and murky in color as the typical butterflies are bright. 

Male Juvenal's duskywing

Pipevine swallowtail
A challenge in butterfly identification that I deal with daily is a group of similarly colored large butterflies I call the "black and blues." They are involved in a mimicry complex based on resemblance to the toxic pipevine swallowtail and can be difficult to separate.  

Female black tiger swallowtail
One commonly seen member is the female black tiger swallowtail; all males are the yellow morph as are many females.  Proportionately more black females are seen to the south where the pipevine swallowtail is found.  The "tails" of the swallowtail are likely false heads to divert the strike of predatory birds away from the vulnerable head region.   Although the mimicry is assumed to be Batesian, in which the toxic pipevine is mimicked by the tasty black morph tiger swallowtail, tiger caterpillars do feed on black cherry trees which contain compounds of cyanide.  

Male spicebush swallowtail
Similarly another mimic, the spicebush swallowtail feeds as a caterpillar on spicebush and sassafras, both of which contain toxic and potentially toxic chemicals.  

So perhaps some day when more information become available, the relationship among these similarly colored butterflies may be found to be more complex than assumed now.  

This is what happened when the previously assumed tasty viceroy was found to be toxic due to its diet of willow.  Thus it is a Muellerian and not a Batesian mimic of the monarch.  Watch for some other members of the fascinating "black and blues," such as the red spotted purple and the female Diana fritillary butterflies.  

I find it both exciting and frustrating that it can be difficult to identify some of the intriguing insects that we encounter daily.  It should teach us that nature is complex and that our systems of categorizing species do not fully represent the range of variation that actually occurs, and that evolutionary change is continuing to occur.

Bill Dunson 
Galax, VA and Englewood, FL 

Thursday, May 14, 2015

Fabulous Flowers of Spring‏

Wake robin, a type of trillium
Although flowers do of course bloom throughout the growing season, the most famous displays of wildflowers occur in early spring before the deciduous tree leaves emerge.  This enables forest flowers to photosynthesize, grow and reproduce before most of the sunlight is blocked by dense tree leaves.  The degree to which this seasonal flush of flowering occurs depends on the type of forest canopy and its density, soil type, moisture, herbivory and other factors.   But in north facing (damp) slopes with rich soil, the floral display can be absolutely amazing.   

Fraser magnolia
Certainly the trees and shrubs can also produce striking blooms and one of my favorites is the Fraser magnolia.  It has an enormous single flower which is believed to be similar to the most primitive flower types.  All of the magnolias, including cucumber trees and tulip poplars, produce nectar and/or fruit which is very attractive to birds.  

Pink azalea
A flower that appears in groups of large single blooms is the spectacular pink or pinxter azalea, a member of the heath family in the genus Rhododendron.  The female stigma extends well beyond the male stamens, presumably a design to reduce inbreeding.  The corolla tube is fairly broad and of intermediate length so that large pollinators such as bumblebees and hummingbirds can access the nectar and still come in contact with the anthers containing pollen.

Fire pink
The design of the fire pink is somewhat similar in that it seems designed to attract hummingbirds and butterflies, with a bright red color and an enlarged tubular corolla tube characteristic of the genus Silene.  

Woodland phlox
In contrast woodland phlox has an extremely narrow corolla tube which would seem to exclude any pollinators that do not have long thin tongues, presumably butterflies or sphinx moths.  Yet bumblebees in our area of VA have learned to bite the base of the flower and steal the nectar without pollinating it.

The showy orchis, a type of orchid, attracts bumblebees with the bluish color of the hood (combined sepals and lateral petals) contrasted with the white lip.  The Wake Robin, a type of trillium, has an entirely different strategy for pollination by emitting the scent of rotten meat to attract flies.  The red buckeye flowers have no scent but are a brilliant red to attract hummingbirds.
Showy orchis

The viburnums have adopted a strategy of massing tiny white flowers together.  Two types in our yard are Maresii and Snowball which pose an interesting contrast since Maresii has many small flowers in the center of the inflorescence with enlarged infertile showy flowers around the outside to attract pollinators.  This same design is found in the wild witch hobble bush.  

Viburnum plicatum maresii
The Snowball variety has been artificially selected to have only the large showy flowers and thus cannot produce fruit since the showy flowers are sterile.  So clearly if you want to attract birds with the fruit, you should plant the types that have fertile flowers.
Viburnum plicatum snowball

The wide variety, color and shape of flowers truly is a remarkable tribute to the intensity of the reproductive drive.  We can enjoy these remarkable objects at a simple level of the beauty that we perceive, or delve further into their specialized evolutionary design which is primarily to attract pollinators.

Bill Dunson 
Galax, VA and Englewood, FL 

Red buckeye

Wednesday, May 13, 2015

Mink alert in Chesnut Creek

My wife and I were biking between Gambetta and the New River along the VA New River Trail and noticed a dark object on a rock in the middle of the creek.  On closer inspection this turned out to be a beautiful and seldom seen mink.  This aquatic weasel was fishing around the rocks and seemed not to mind our scrutiny.  So while biking and hiking keep your eyes open for unusual sights and sounds- as a "famous philosopher" once said- you never know what you are going to get !

Bill Dunson