Tuesday, June 28, 2016

MD Herps - Copperhead (Agkistrodon contortrix)

The copperhead (Agkistrodon contortrix) is one of Maryland's most notorious snakes.  Like most venomous snakes, it is both widely feared and misunderstood. This, unfortunately, not only causes the unnecessary death of copperheads, but also a variety of other snakes that are misidentified as such.  In this post, we'll get to know this infamous snake, and learn methods of living alongside these maligned reptiles.

A copperhead snake. Notice the dark hourglass patterns with their "waists" over the spine. 
COPPERHEAD ID CHECKLIST:

  • colored in shades of reddish-brown and tan, bearing a striking resemblance to fallen leaves
  • patterned in dark hourglass-like bands with the skinny "waist" of the hourglass over the spine
  • scales are keeled and not shiny
  • head is broad, with the "cheeks" being very distinctively wider than the "neck"
  • no rattle (though will sometimes shake the tip of its tail)
  • vertical pupils
  • relatively stocky, fat body

NATURAL HISTORY

Of the 27 different species and subspecies of snakes in Maryland, only two are venomous to humans - the copperhead and the state-rare timber rattlesnake (Crotalus horridus). Both the copperhead and the rattlesnake are pit vipers, a group of venomous snakes that have a heat-sensing pit between their nostril and eye on either side of their head.  In general, this feature gives this group an exceptional ability to hunt warm-blooded prey at night.  Overnight, the plants, stones, and soil cool down without the heat of the sun, but warm-blooded animals, such as rodents, remain hot.  The pits are sensitive to the infrared light emanating from warm objects, essentially highlighting mammals in in the darkness.

Notice the pit between the eye and the nostril of this copperhead. 
While adult copperheads take a large number of rodents as part of their diet, juvenile copperheads have an additional adaptation - the tips of their tails are a striking yellow-green.  The young copperheads will lay camouflaged in the leaves and wiggle their tails like a squirming grub.  This acts as a lure, which attracts lizards and frogs as prey for the small snakes.  This diet high in cold-blooded prey is fairly unusual among pit vipers. As the copperheads mature, their tails darken, and they turn to a diet mainly of mice and voles, though they will continue to eat amphibians and reptiles when available.  They have even been known to eat birds, smaller snakes, and large insects, such as cicadas! Like all of Maryland's snakes, however, children, dogs, and cats are far too large to eat, and are off the menu.

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A juvenile copperhead, wiggling its yellow-green tail. Image public domain via Wikimedia Commons
Copperheads hunt by using their keen sense of smell to locate areas where prey frequent, then set up camp, lying motionless in the leaf litter for days, or weeks, until food comes within striking range. Prey is subdued by a hemolytic venomous bite that destroys red blood cells.  While dangerous to small animals, the venom of copperheads is actually weak among vipers, and is typically not fatal to humans.  Regardless, all bites should receive medical attention to treat pain and prevent damaging complications due to swelling or secondary infections.  While adult humans generally experience non-fatal, though unpleasant, effects of copperhead bites, such as pain and nausea, they can be more dangerous to children and pets due to their smaller body size.

Bites from copperheads, however, are fairly rare.  The copperhead's venom has evolved to allow it to capture prey, not fend off large animals.  Its main defense against disturbance by humans is to sit motionless and allow its near-perfect camouflage to render it invisible.  If further provoked, it will often try to slither away, rather than bite.  Most bites occur when they are accidentally stepped on, or when humans are trying to handle or kill them.  One of the best ways to prevent copperhead bites is to not try to kill copperheads!

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A copperhead's camouflage is near-perfect!  Image public domain via Wikimedia Commons.
Another common misconception about copperheads involves their habitat.  Folk knowledge places copperheads near bodies of water, but copperheads are just as likely to occupy wet habitats as they are dry environs. The association of copperheads and water possibly stems from confusion between copperheads and water snakes and water moccasins, both of which prefer wet habitats.  Water moccasins are not found in Maryland, but are close relatives of copperheads.  In fact, in the southern states, copperheads are sometimes called "highland moccasins" or "dry-land moccasins" due to their habit of living in much dryer areas than their cousin.

In truth, copperheads are not particularly picky about their habitat type - they can be found along rivers, in wetlands, on dry slopes and ridges, sandy woodlands, and hilly forest.  While many of these habitats tend to have a water source nearby, it isn't a always a requirement for copperheads. Copperhead habitats commonly feature rocky areas or dense woodpiles that can can provide shelter throughout the year or hibernation dens during the cold months. Good hibernacula can be few-and-far-between in some areas, and copperheads tend to hibernate together and with other species of snakes, including rattlesnakes and rat snakes.

Rocky areas, like this in the Catoctin Mountains, make good snake habitat. 
In spring, after emerging from hibernation, copperheads tend to bask around their winter dens before dispersing, sometimes long distances, in search of feeding grounds.  This is also the start of their first breeding season, the second breeding season beginning in fall.  Females who mate in the spring will give birth that season, but those who mate in fall will store the sperm and give birth the following year.

Mother copperheads show a remarkable amount of parental care for their young.  They do not lay eggs, but rather, carry their developing young inside them for several months, then give birth to fully-developed young snakes.  This allows the female to provide better protection and thermoregulation of her young than she would be able to provide for a batch of eggs. After they are born, the young stay with their mother until their first shed, giving them additional protection and a head-start to life.

Young copperheads are at risk from a large number of predators, including a variety of predatory birds, larger snakes, cats, opossums, and even large bullfrogs!  Many copperheads will die before they reach maturity at 2-4 years.  The oldest recorded wild copperhead was 18 years old, but they can live almost 30 years in captivity if provided good care.  Copperheads are sometimes cared for by educational, conservation, and research institutions, and their venom may have anti-cancer properties which are being explored.  As venomous snakes, they are not legal to keep as personal pets in Maryland.

COPPERHEADS IN MARYLAND

In Maryland, we have two distinctive populations of copperheads.  The northern copperhead (A. c. mokasen) is found throughout the state, except for the Delmarva peninsula. Its numbers are highest in western Maryland and decline eastward toward the coastal plain.  The second group of copperheads are an intergrade population between the southern copperhead (A. c. contortrix) and the northern copperhead.  They are found on the southern portion of the Delmarva peninsula.  Northern copperheads are generally darker than their southern cousins, and often have dark blotches between their hourglass markings, while southern copperheads tend to be lighter and without excess blotches. Intergrade copperheads have characteristics of both subspecies, being somewhat lighter and less blotched than northern copperheads, but darker and more spotted than true southerns.  Copperheads are rare to non-existent on the northernmost portion of the Delmarva peninsula.

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A typical northern copperhead (A. c. mokasen). Image public domain via Wikimedia Commons.
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A typical southern copperhead (A. c. contortrix). Image public domain via Wikimedia Commons.
LIVING WITH COPPERHEADS

Copperheads spend most of their time hidden from sight, either within rock crevices, under brush, or by sitting perfectly still and camouflaged.  Copperhead bites can be prevented in a few ways:

  • Take care when walking through brush, over logs, and in rocky areas, particularly if you are not using established trails, as copperheads can be very difficult to spot in undisturbed leaf litter
  • Check hand- and foot-holds carefully when rock climbing
  • Wear long pants when hiking, and wear protective clothing when moving brush or clearing debris in natural areas
  • Never try to handle or kill a copperhead if you find one
  • Carefully monitor pets and children when playing or traveling in areas where copperheads are suspected of living
  • Avoid known hibernation sites
What should you do if you find a copperhead?
  • In most cases, all you need to do is leave it alone and appreciate the opportunity to view one of Maryland's most cryptic snakes - don't try to touch or scare it, just let it do its thing. 
  • If the snake is in a location that requires it to be moved (in a home, garage, in a busy path, etc.) contact the Maryland DNR or visit this site to find a licensed wildlife control officer.  Do NOT try to handle or kill it. 
  • Sometimes snakes appear dead when they are sick or injured.  Even if a copperhead appears dead, do not attempt to handle or move it, and instead contact your county's Animal Control service for dead animal pick-up.  If you suspect the animal is sick or injured, contact a licensed wildlife rehabilitator.
  • In the case of a copperhead bite, seek medical attention immediately!  Even though copperhead venom is relatively weak and rarely fatal, it can cause medically significant symptoms and lead to potentially dangerous complications if untreated. Animals suspected of being bitten should receive immediate veterinary care. 
SIMILAR SPECIES

Many Maryland snake species are frequently confused for copperheads.  Copperheads and rattlesnakes are pit vipers, and have several features unlike Maryland's non-venomous snakes. 

MARYLAND VENOMOUS SNAKES
  • Heads are very distinct from body, with their fat "cheeks" much wider than their "necks"
  • Relatively thick, stocky bodies
  • Vertical, cat-like pupils
MARYLAND NON-VENOMOUS SNAKES
  • Heads are rounded, like polished stones, and are indistinct, with their necks only slightly thinner than their heads
  • Most are long and skinny
  • Round pupils
A copperhead next to a timber rattlesnake.  Notice the distinctly wide head that is characteristic of vipers. Also notice the difference in pattern between the copperhead and rattlesnake.
Copperheads can also be easily distinguished from rattlesnakes as follows:

COPPERHEAD:
  • Distinct hourglass-shaped bands that are thinnest over the spine
  • Colored and patterned like crisp, fallen leaves
  • No rattle
  • Our most common venomous snake
TIMBER RATTLESNAKE:
  • Dark, tiger-stripe or zig-zagged bands that are widest over the spine
  • Typically gray or tan with dark bands, like strips of tree bark
  • Rattle on tip of tail
  • State-rare
A adult copperhead tail (no rattle) next to a timber rattlesnake tail (rattle). The body of the timber rattlesnake is in the background. 
The most common snakes confused for copperheads are northern water snakes, possibly because copperheads are strongly, but somewhat erroneously, associated with bodies of water. Corn snakes and milk snakes are also frequently mislabeled as copperheads because of their reddish coloring.  Water snakes, corn snakes, and milk snakes all have round pupils, heads that are only slightly wider than their necks, and dark blotches/bands of color that are widest over their spines. 

A northern water snake, frequently mistaken for a copperhead. 

REFERENCES:

Animal Diversity Web, University of Michigan

Maryland Biodiversity Project

Maryland Department of Natural Resources, "Snakes in Maryland."

Maryland Department of Natural Resources, "Field Guide to Maryland Snakes: Northern Copperhead."

Smithsonian National Zoological Park, "Fact Sheet: Northern Copperhead"


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