A person goes to a fancy restaurant and finds the menu has no prices listed. The person wonders whether he can afford to eat there. The answer is "If you have to ask, you cannot afford it."
My experience has been that head shape is a very unreliable identification characteristic. With training and experience, a person can identify many venomous species based upon head shape. However, most persons do not have such training and experience. Like the restaurant customer, if one has to rely upon head shape for identification, one cannot make an accurate identification.
Most venomous snakes in the United States are pit vipers. Pit vipers have large, wide heads and narrow necks. They also have bulging venom glands on top of each side of their head. This shape is often referred to as an "arrowhead" shape. Some of our nonvenomous snake species have large heads and narrow necks. The term "arrowhead" shape is not precise. I have found many Native American arrow and spear points in my life. Their shapes range from triangles to ovals. I expect I could match a point's shape for every snake species' head shape. The situation is further complicated by the fact that many nonvenomous snake species change the shape of their heads when in a defensive posture. They do this by flattening their heads to make them wider. Large species such as water snakes and small species like Brown Snakes do this. Here are pictures of a Cottonmouth (venomous) and a Banded Watersnake (nonvenomous). Which has the most arrowhead-shaped head?
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By far, the snake species that is most often found in houses and buildings is the Black Rat Snake (Elaphe obsoleta obsoleta). Black Rat Snakes are large nonvenomous snakes which eat rats, mice, squirrels and birds. Black Rat Snakes and its subspecies (Yellow, Gray, Everglades, and Texas) are found throughout the eastern half of the United States. In South Carolina, they are an abundant species.
There are three reasons why Black Rat Snakes get in homes and buildings so often. First, they are abundant. Second, their principal prey, rodents and birds, thrive around our homes and buildings. And third, they are excellent climbers. Black Rat Snakes hunt by scent and sight. They can follow the trail of a mouse or squirrel along its secret path into our homes, no matter whether the trail leads through the crawlspace or the attic.
Adult Black Rat Snakes have shiny, jet black backs and show very little pattern. Yellow Rat Snake backs are yellow/olive and show 4 dark stripes; Everglades Rat Snakes are similar but have an orange background color. Gray and Texas Rat Snakes are heavily blotched. Juveniles of all subspecies are blotched.
Rat Snakes will attempt to remain unseen by freezing in place when first threatened. This strategy leads to many of them being killed on our roads. However, even newborns will assume a striking defensive posture when cornered and harassed. They will bite and adults can puncture the skin. They will also emit a strong musk smell.
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I am not the best source for information about keeping snakes away. I have always sought them and never tired to keep them away. Thus I have not tried any of the folk methods for repelling snakes, nor any of the commercial products offered for such purposes. However, in searching for snakes I look for environments which attract snakes. It follows that lowering the attractiveness of a yard to snakes is a method of repelling snakes. Therefore, I can describe some environmental factors which attract snakes and you may wish to avoid or reduce them your yard. However, you may find that many features that you find attractive in your yard are also attractive to snakes. Everything is a balance between benefits and costs. Personally, I think it would be much better for you to learn to share your yard with snakes, just as you do with other native wildlife.
Snakes can be discouraged from a location by less food, reduced shelter, and more predators. They can also be diverted using physical barriers.
Food: All snakes are carnivores, that is, they eat other animals. Larger native snake species which often enter our yards eat rodents, birds, lizards, and smaller snakes. Each of these prey have adapted well to living with humans. They make their homes in the trees, scrubs, and flower beds we cultivate in our yards. Squirrels, rats and mice often live in our homes and buildings. We put out feeders to attract birds and squirrels. The more prey animals we invite into our yards, the more snakes will be attracted.
Shelter: Due to the nature of their physiques, snakes are very vulnerable creatures. Very few of our native snakes can successfully thwart an attack by a cat or dog. Their best defense is to be cryptic or unseen. Availability of shelter is the key to this defense. The more places to hide, the more attractive your yard will be to snakes. A snake will cross an open area of yard with much reluctance. Leaf litter, tall grass, weeds, vines and scrubs provide cover for snakes while moving. When not moving, they prefer to hide beneath something. Boards, trash, and yard objects provide cover for snakes. A broad border of well-trimmed lawn is a great discouragement to a snake.
Predators: Dogs and cats are major predators of snakes in suburban areas. Most dogs will attack and kill even our larger species. Domestic cats are particularly effective in reducing snake populations. Yard cats kill many small snakes. They also kill many birds, mice, and lizards which might otherwise be food for snakes. Yard fowl, such as chickens, turkeys, and guinea hens, are also predators of small snakes.
Physical barriers can also be useful in repelling snakes. Although it is very difficult to make a fence which will absolutely prevent a snake from crossing, fence-like barriers can be used to guide snakes away from your yard. For example, rock wall can be traversed by many snakes. However, if the wall is free of scrubs and vines, the snake will be fully exposed to predators while on the wall and thus will be reluctant to cross. The wall then functions as a barrier which directs the snake along its length. Strategically placed, such a wall can divert snakes away from your yard.
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For identification, I rely most heavily upon:
Peterson Field Guides "Reptiles and Amphibians, Eastern/Central North America"
by Roger Conant and Joseph T. Collins,
by Houghton Mifflin Company.
For herps specific to South Carolina and neighboring states, I like:
Amphibians and Reptiles of the Carolinas and Virginia
by Bernard S. Martof, William M. Palmer, Joseph R. Bailey, and Julian R. Harrison III,
University of North Carolina Press.
Specifically for snakes there is a new book out that I like a lot:
Snakes of the Southeast
by Whit Gibbons and Mike Dorcas,
University of Georgia Press.
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