Monday, February 9, 2015

Slug Caterpillars of Maryland

                       



                  SLUG CATERPILLARS

                         of MARYLAND
                                       
Recently revised in January 2020 with updated information and rankings. 

As any Maryland nature photographer who’s ever ventured afield knows, there is no creature large or small, which fuels more passion and fascination than members of Family Limacodidae…Slug Caterpillar Moths.
The diverse beauty of these tiny obscure creatures is surpassed only by the covert solitary roles they play in the Web of Life.  
This synopsis was compiled as an introduction to the different species one would most likely encounter within Maryland’s woodlands. 
This account is by no means scientific. It is just one photographer’s compilation of specimens discovered and photographed during many years of searching. 

Since some slug caterpillar species are more likely to be seen than others, I’ve listed them in the order of commonality…at least as applied to my rate of success in finding them. 
Before we meet each member face to face, a brief discussion about the Family in general seems in order. 
Limacodidae for the most part, are solitary creatures. For that reason it’s quite unlikely to find more than one individual occupying a single leaf. They seem to prefer dispersing soon after birth to stake their own claims.
(The only exception to this rule that I've observed will be discussed later.)

Summer and Fall
Maryland‘s slug caterpillar season typically begins in July and lasts through mid-October. The peak time is from late August to mid-September. During this prime time, most of the tiny caterpillars have realized their largest potentials for growth and are easiest to find.
Early in the season they are really tiny…appearing to the naked eye as minuscule specs on the leaves that will become their feeding grounds for the coming months as they develop and grow.
             
                                                   
Size Matters


This comparison photo, taken during the first week of August, illustrates just how tiny these early instars really are.
…not to worry though. By the time September rolls around, this same little guy will likely have quadrupled in size and he (or she) will be as easy to spot as an old penny.

Turn Over an Old Leaf
Like most caterpillars, it’s certainly no secret that slugs prefer hiding on the undersides of the leaves. While great for them, this behavior makes it much more difficult for us nature-types to find them.
It's also been proven that slugs (like most caterpillars) prefer old, mature leaves over new growth, where the chlorophyll they crave is more potent. 
       
                  
                                 
As illustrated in the photos above, the topside of a group of oak leaves yields no indication of what lies beneath. Searching the underside of one of the leaves reveals all.
Through experience, I’ve incorporated an effective method to use for this painstaking style of searching.
I've  learned the hard way never to grab onto individual leaves. I prefer to carefully snake my arm through the canopy of leaves and firmly grasp a crotch in the branch…then twist the entire branch to reveal the undersides of all its leaves.
Not only is this method a huge time-saver, but it eliminates the possibility of getting a thumb full of hurt from a pissed off Saddleback or other stinging critter. (That is something no one wants to do more than once.)

To find a pearl…you have to shuck a LOT of oysters.
This axiom certainly rings true when seeking slug cats in the wild.
Too often one can consume hours of searching between discoveries.
It helps to narrow search criteria to capitalize on the best possibilities for success. For me, this translates into keying almost entirely on oak.
While cherry, sycamore, walnut and other tree species will also host slug caterpillars…just about every member of MD’s catalog of Limacodidae species lists oak among their preferred trees of choice.
I take this acquired knowledge a step further and concentrate mostly on low-level scrub oak or oak saplings. This narrows the search area even more... surmising that I’m much more likely to find that obscure needle in a smaller haystack.
In areas of the forest where you know the slug caterpillars you seek are present but there aren't many oak trees, you can also search the leaves of witch hazel...particularly when that's the dominate tree species within a particular region.
I've also learned recently that most of the caterpillars I've found (including slugs) are on trees and foliage along roadsides or forest edges adjacent to open fields. 
Why this is true is unknown. 
My theory is that is has something to do with the flight patterns of the adults depositing their eggs.
(Could it possibly be that it's easier for gravid adults to fly around in open areas...or perhaps that the open fields and roadsides provide more sunlight for incubation?)
It could also be that edges provide more diversity in foliage from which to choose.
For whatever reason, this scenario seems consistent enough that I've modified my search criteria. I rarely spend much time within the deep-wooded areas of the forest these days.

      
               MARYLAND SPECIES LIST

As mentioned earlier, this list of slug caterpillar species has been ranked in the order of occurrence and commonality to Maryland woodlands. This list does not represent all of the species found within Maryland’s boundaries. These are only representative of the ones I’ve been able to find. 
The lower numbered ones will be the most prevalent during a given outing, while the higher numbers represent species which are more rare.
Again, I would like to stress that the information provided is not to be construed as scientific fact…but rather as chronicled results from my own experiences.

                       #1 Saddleback Caterpillar (Acharia stimulea)

My first introduction to this fascinating little creature was years ago, and I was that excited kid left alone in the candy store. At that time, it seemed surreal. It hardly seemed possible that something this bizarre in appearance was actually alive! 

Now, I seem to be finding them everywhere, on a variety of trees and shrubs.
A. stimulea ranks #1 on my list because it is a very common species here in Maryland and beyond. 
Saddlebacks also rank high on the “poison meter”, as they can deliver a painful sting to the careless. 


Saddleback Caterpillar with Braconid Parasites

                                       Saddleback Cluster on Aspen

The Saddleback is also the only slug species I've ever observed clustering as a group, even long after the brood had hatched. While most slug species immediately disperse, Saddles seem to prefer back-to-back coverage throughout their earlier instars. 


            
                                       
                     #2 Yellow-shouldered Slug (Lithacodes fasciola )
                                          A Shoulder to Cry On

L. fasciola is another very common Maryland species. It's too often a time-waster, happened upon while searching for something else. 
Many of the Yellow-shouldered specimens I’ve encountered have been infested with Braconids or other parasites. This vibrant individual seemed to justify the time I spent photographing it. Usually, I just ignore them and move on. 
Yellow-shouldered Slugs  typically feed on the leaves of sycamore, oak and other woody trees. Their coloration ranges from olive to lime green, with random iridescent specks of yellow.

                            
                                  #3 Crowned Slug (Isa textula)
                                               A Crowned Jewel

Photographically speaking, Isa textula ranks among the most prized of all of the slug caterpillar species found in Maryland. It’s unique design and textures beg to be captured.
Fortunately, Crowned Slugs are very common and are likely to be encountered on just about every summer and fall outing. On a good day in prime habitat, it’s possible to happen upon a dozen or more of these fanciful creatures. 
Sadly though, they all seem to look exactly alike. 
(…so if you've seen one, you've seen ‘em all.)


                             #4 Skiff Moth (Prolimacodes badia)
                                                Colorful Skiff

While P. badia may be highly variable in color, it’s shape is truly unique and identifiable.
Skiff Moth larvae have been known to feed on a variety of tree species. Their unpredictable coloration, commonality, and their propensity to remain completely motionless, helps to rank the Skiff high on the list of targeted species for bug photographers.
I seldom pass on the opportunity to photograph one of these amazing creatures.

                                   Skiff Moth with Crowned Slug

This image helps attest to the Skiff’s diversity in color and pattern.
Every one is unique. This particular Skiff Moth happened to be sharing its leaf with a Crowned Slug. During the ensuing photo session, the Crown awoke and began “racing” across the leaf…as fast as a tiny slug could.
(If you look closely, you can see a bit of slug-trail behind it.)


                              #5 Smaller Parasa (Parasa chloris)
                                               The Classic Slug

Parasa chloris is an amazing little creature and is more common in Maryland than I’d first thought.
In 2014 alone, I found over a dozen of these guys, representing various stages of development…while previous years had revealed only a few.
This particular specimen was an inch long.
..that's HUGE!
In photographing them, you can pretty much count on P. chloris waking up early during the session and moving around.
…so shoot quickly!


                     #6 Purple-crested Slug (Adoneta spinuloides)
                                            Colorful Kielbasa

The Purple-crested Slug has an elongated body shape. It’s coloration is variable, but usually contains red-maroon splotch patterns along its back. 
A. spinuloides is similar in shape to the much rarer Long-horned Slug (Adoneta bicaudata), which sports elongated appendages (horns) near its tail.
Purple-crested Slug Moths are wide-spread throughout the state.


                                    #7 Button Slugs (Tortricidia)
                            Red-crossed Button Slug (Tortricidia pallida)


                             Abbreviated Button Slug (Tortricidia flexuosa)

Tortricidia species are wide-spread throughout Maryland, but most commonly encountered in the higher elevations. Button slugs are usually the first slug moth caterpillars to begin showing up each summer. Like all caterpillars, they start out very tiny and progress through various size and color changes as they develop and grow.
Positively identifying individual encounters to actual species is a nightmare scenario best left to the experts. Their pattern and coloration varies too much from one individual to the next for neophyte naturalists to accurately identify particular species with certainty.
What I have observed, is that all Button Slug species seem to love oak, sycamore and witch hazel. My searches have revealed more specimens on these three trees than all others combined.
I've ranked them at #7...around half-way through the “rare matrix”, since finding these cute little guys can be hit or miss. They appear to be regional, in that one small patch of woods will have a bunch of them, while a few acres away seems to be button-free.

                             #8 Nason’s Slug Moth (Natada nasoni)
                                        Late Instar Nason's

Natada nasoni ranks among my personal favorites. 
Nason’s vivid colors and patterns fully manifest themselves during later instars. Juvenile specimens are drab-olive in color with much more subtle design.
In Maryland, I’ve found these mostly from Carroll County eastward to Harford County. They're always a welcomed find.  


                 #9 Jeweled Tailed Slug Moth (Packardia geminata)

           
                #10 Elegant Tailed Slug Moth (Packardia elegans)



These two similar specimens represent a “tale of two tails”…so to speak.
The only places I've found these tailed slugs is in a tiny section of remote woods within the Catoctin Mountains west of Frederick, and along a stretch of Deer Creek in Harford County. Each year, they appear most prevalent during a brief three week period in August. Both varieties seem to prefer oak and witch hazel. P. elegans also has an affinity for beech. 
P. geminata specimens are typically found a few feet off the ground.
At first glance, I thought that both were a variation of the ubiquitous Yellow-shouldered Slugs I see everywhere. Their elongated bodies and pronounced “tails” prompted further scrutiny.
They both deserve high marks on my rare meter, since I've only found them in random sections of woods during a very limited time frame.

                     
                      #11 Shagreened Slug Moth (Apoda biguttata) 
                                            
Shagreened Slugs are slightly elongated, olive green in color and sport a distinguishing pair of white (or yellow) “racing stripes” along the entire dorsal.
My first confirmed encounter with this particular species was during the summer of 2013…and I've found very few of them since.
In Maryland, they seem to rank very high among the “seldom seen” class.
Apoda biguttata is a welcomed find and a handsome addition to anyone’s life-list. 

           #12 Beutenmueller's Slug Moth (Isochaetes beutenmuelleri)
                                            Spun Glass...a Living Jewel

                                                  A Pair of Glasses

It’s no question that this crystalline, angelic life form deserves high marks on my list of slug caterpillars found within Maryland’s boundaries.
Before spotting one of these alien-looking creatures during the summer of 2014, I’d only seen Spun Glass Slugs gracing the pages of my guide books. I've since found quite a few more, and consequently, moved this species further back in the ranks of my "rare meter". 
I. beutenmuelleri prefers oak and beech, and is highly prized among moth and caterpillar hunters.
Later instars can be very difficult to photograph. They tend to wake up and start squirming around when disturbed. 
                                                             Spun Glass Dance

Also, avoid using flash as much as possible. There will be harsh flash-back from their glass-like bodies.

                        
                             #13 Spiny Oak Slug (Euclea delphinii)
                                               The Holy Grail


           Spiny Oak Discolored (possibly due to parasite infestation)

I’ve often referred to E. delphinii as the Holy Grail of Caterpillar Species.
He’s The Slug of 1000 Hours. At least it seems that way.
During my years of specifically searching for these elusive creatures, I've found a dozen or so confirmed specimens in Maryland.
Most were found in the high elevations of the Catoctin Range west of Frederick, and at Lost Land in Garrett County. A handful of others were found in Harford and Carroll Counties.


                                    Euclea delphinii in Garrett County

Spiny Oak Slugs prefer to remain hidden from view…sometimes sandwiched between two adjoining leaves or tucked under a fold. They prefer oak, but I've found them also on maple, tupelo, hickory and beech. Recent encounters on locust and dogwood were, most likely, individuals which had migrated from nearby hosts.  
These guys are quite rare, so the only advice I can give is to search…and search…and search again. You will find multitudes of other stuff to keep you busy, but don’t give up. 

                            #14 Hag Moth (Phobetron pithecium)
                                                Monkey Slug

I will preface this discussion by declaring that this Hag has been the monkey on my back for far too long.
It’s not often I’ll target a particular species so vehemently and with such conviction. For around 5 years, I've meticulously searched, trees, brush and roadside brambles to no avail. My hope to find one seemed an unattainable goal. 
How could this be? Others were finding them. Granted, not every day, but certainly often enough for me to question my methods.
Then during the summer of 2014, the drought was finally broken. I found not one, but TWO Hags…on consecutive trips. Since then, I've found only a handful of others. Monkey Slugs can be found on a variety of trees and shrubs. Unlike most slugs, Hags prefer to rest in plain sight on the tops of leaves.
(..now, if I could find a way to photograph them so they don’t look so damn ugly.)

                           #15 Long-horned Slug (Adoneta bicaudata)

As mentioned earlier, Long-horned Slug Caterpillars are similar in design to Purple-crested (A. spinuloides), but are considerably more rare. 
A. bicaudata deserves a high number on my list of Maryland slug caterpillar species, given how few I've been able to find.
Like most slug caterpillar species, Adoneta bicaudata can be found clinging to the undersides of oak leaves. 
This handsome specimen was found in Carroll County, Maryland in late October 2015. 
Slug caterpillar season typically ends much sooner and I consider myself lucky to have found this lifer so late in the season.
Lately, I've been finding late-summer Long-horned Slugs in the Catoctin Mountains, west of Thurmont.
Other encounters in Calvert and St. Mary's Counties suggest that A. bicaudata may be more of a southern species...predominant to the counties of Maryland's lower Eastern and Western Shores.

                         
                            #16 Stinging Rose Caterpillar (Parasa indetermina)
                                                            Stinging Rose (Yellow Phase)


                                                          Stinging Rose (Red Phase)

This elusive creature deserves top billing in my list of Maryland slug caterpillar species. Stinging Rose is a coastal resident, found along the briny shores of the Atlantic.
These two were photographed along the New Jersey coast, but reports of encounters along portions of Assateague Island suggests that they do exist in Maryland. So far to date, repeated searches have revealed no Stinging Rose caterpillars within Maryland boundaries...though I remain optimistic.
Search coastal bayberry shrubs along trails and roadside edges during late summer and early fall. 
Avid New Jersey caterpillar hunter David Moskowitz suggests hunting at night with an ultra-violet lamp to maximize the potential for finding these colorful living jewels. 


© Bob Cammarata 2015
bobcammarata.blogspot.com

No portion of this material may be copied or used without permission


          

8 comments:

  1. This has instantly become my bible for shooting cats! Tremendous job, Bob!

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  2. What interesting and informative articles and amazing images, Bob! Well done!

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  3. you wouldnt think i'd be all giddy at finally finding out about slug cats, buuutt, i saw footage of a skiff moth caterpillar online, but NO identifying information was given. I was on a quest !! How had i never heard of or seen this slug? i just about live in the woods, weather permitting; I've been hiking for 50 yrs and never saw or heard of slug caterpillars. What i'm saying is that i got only a visual on this critter and spent WEEKS trying to read all sorts of bug sites but still could not pin down this slug's i.d. Color me relieved. Jeez, i feel so much better now that that is solved. And yes, your site is the best --- esp like the occasional witty comment here and there. And why can't i find photos of the undercarriage of the skiff moth cat? the unidentified one on you tube was very red and gelatinous underneath. I want to study the whole bug, not just the top. Still not sure why as it's kinda gross. Thanks

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    Replies
    1. Slug cats are indeed quite intriguing and photogenic. Thanks for the nice comments!

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