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 

No comments:

Post a Comment