Don't tread on me: an examination of the anti-predatory behavior of Eastern Copperheads (Agkistrodon contortrix)

Abstract

Venomous snake species across the globe have been historically categorized as aggressive and dangerous, leading to widespread persecution and killings. Despite the conservation importance of educating the public about the docile nature of these species, few studies have attempted to quantify the response of viperid species to human interactions. Here we report the responses of free-ranging copperheads to a potential human encounter using a set of hierarchical behavioral trials. Out of a total of 69 snakes, only two individuals feigned striking and only two attempted to bite (3% of all individuals). Our results support the findings of previous studies documenting the docile nature of other viperid species and can hopefully be used to change the public perception of venomous snakes. Convincing the public and policy makers that viperid species are docile is critical to long-term conservation of these species in the U.S. and around the globe.

Full text

Acta Herpetologica 15(1): 31-37, 2020
ISSN 1827-9635 (print) © Firenze University Press
ISSN 1827-9643 (online) www.fupress.com/ah
DOI: 10.13128/a_h-7757
Don’t tread on me: an examination of the anti-predatory behavior of
Eastern Copperheads (Agkistrodon contortrix)
A A,,*, J G, S M, E B, H H,
1 STEM Division, Harford Community College, 401 omas Run Road, Bel Air, Maryland, 21015, USA
2 Susquehannock Wildlife Society, 1725 Trappe Church Road, Darlington, Maryland, 21034, USA
3 Department of Biology, University of Miami, 1301 Memorial Drive, #215 Cox Science Center, Coral Gables, Florida, 33146, USA
* Corresponding author. Email: anadams@harford.edu
Submitted on: 2020, 13th January; revised on: 2020, 10th April; accepted on: 2020, 14th April
Editor: Marco Sannolo
Abstract. Venomous snake species across the globe have been historically categorized as aggressive and dangerous,
leading to widespread persecution and killings. Despite the conservation importance of educating the public about
the docile nature of these species, few studies have attempted to quantify the response of viperid species to human
interactions. Here we report the responses of free-ranging copperheads to a potential human encounter using a set of
hierarchical behavioral trials. Out of a total of 69 snakes, only two individuals feigned striking and only two attempted
to bite (3% of all individuals). Our results support the ndings of previous studies documenting the docile nature of
other viperid species and can hopefully be used to change the public perception of venomous snakes. Convincing the
public and policy makers that viperid species are docile is critical to long-term conservation of these species in the
U.S. and around the globe.
Keywords. Human-wildlife conict, optimality theory, venomous species, Viper, Viperidae.
INTRODUCTION
As human populations continue to grow and
encroach further into uninhabited or sparsely populated
areas, there is a subsequent increase in the prevalence of
human-wildlife conict (Woodroe et al., 2005; Skogen
et al., 2008; Dickman, 2010). e outcomes of human-
wildlife conict are rarely more pronounced and poten-
tially lethal to both parties than the interaction between
humans and venomous snakes. Venomous snakes have
long been a source of great fear for the general public,
and have been historically (and currently) mischaracter-
ized as being aggressive and dangerous (Blythe, 1979;
Seigel and Mullin, 2009; Burghardt et al., 2009; Pan-
dey, 2016). Even scientic medical publications describ-
ing envenomations as late as 2002 (Juckett and Hancox,
2002) continued to perpetuate the myth that viperid spe-
cies like the cottonmouth (Agkistrodon piscivorus) are
aggressive and readily attack humans. Misinformation
and negative public perception have led to the wholesale
slaughter of venomous pit vipers across North Amer-
ica and Europe. Events such as Rattlesnake and cop-
perhead roundups in the US (Adams et al., 1994; Fitch,
1998; Burghardt et al., 2009), and the killing of individ-
ual snakes, such as the meadow viper (Vipera ursinii),
the Cyperian Blunt-nosed Viper (Macrovipera lebetina
lebetina), and the Northern adder (Vipera berus) when
they are encountered in Europe (Edgar and Bird, 2006;
Stumpel et al. 2015, Julian and Hodges, 2019) are exam-
ples of direct persecution against viperid species. is
widespread persecution continues to take place in both
areas, and is a serious conservation concern for many
viperid species, despite these species causing very low
numbers of fatalities across these two continents (Chip-

32 Andrew Adams et alii
paux, 2012). It is imperative that any conservation action
plan seeking to protect these species will need to incor-
porate some type of public outreach to reduce direct per-
secution of these species (Seigel and Mullin, 2009).
Despite the largely negative public perception sur-
rounding pit-vipers, papers have been published in
the last two decades that clearly demonstrate the pas-
sive and even cowardly nature of other viperid species
(Shine et al., 2000; Gibbons and Dorcas, 2002; Glaudas
et al., 2005). If snakes are confronted by a large potential
predator, the decision to no longer rely on passive defen-
sive behaviors and strike could have a host of potentially
short and long-term negative consequences for the snake
(Gibbons and Dorcas, 2002; Broom and Ruxton, 2005).
For cryptic species, optimality theory predicts that the
most ecient strategy to both reduce energy waste and
avoid potential mortality is to remain in hiding if pos-
sible and to ee immediately if detected by the preda-
tor (Ydenberg and Dill, 1986; Broom and Ruxton, 2005;
McKnight and Howell, 2015). Like other cryptic species
responding to large predators, cryptic viperid species
should rely primarily on crypsis or eeing as primary
sources of predator evasion, followed only aer these
two tactics have failed, by striking and envenomation.
When confronted and detected by a potential predator, a
snake should rst attempt to escape, then employ a suite
of passive deterrents (e.g., musking, tail vibrating, mouth
gaping), and nally commit to active defenses (biting or
striking; Roth and Johnson, 2004).
In addition to the decision-making process driven
by optimality theory (see Ydenberg and Dill, 1986), there
are a host of intrinsic and extrinsic factors that may act
to mediate the chance that a snake will strike (Cooper
and Vitt, 2002; Roth and Johnson, 2004). Intrinsic fac-
tors such as size (Hailey and Davies, 1986; Whitaker and
Shine, 1999), body temperature (Layne and Ford, 1984;
Goode and Duvall, 1989), sex (Scudder and Burghardt,
1983), time since feeding (Herzog and Bailey, 1987), prior
predator exposure (Glaudus, 2004), and gestation may all
play a role in the likelihood of striking (Glaudas et al.,
2005). However, studies have found contradictory results
regarding the role that each of these factors may play,
suggesting that the exact inuence of these factors are
likely species specic (Roth and Johnson 2004). Extrinsic
factors like the severity of the threat and the relative loca-
tion of the snake may also impact strike likelihood (Gib-
bons and Dorcas, 2002; Shine et al., 2002; Glaudas et al.,
2005).
e Eastern copperhead (Agkistrodon contortrix) is
perhaps the most commonly persecuted snake species in
the Eastern US. is wide-ranging species can be found
throughout the eastern United States from Massachu-
setts to Florida, west into Texas and across a wide vari-
ety of habitat types (Ernst and Ernst, 2003). Copperheads
are an ideal species for a study examining the defensive
behavior of a Viperid species to human presence and
subsequent interaction, because they are widespread
across the heavily populated areas of the Mid-Atlantic
and Southeastern US, are responsible for a large propor-
tion (49.2%) of the reported envenomations in the US
(Gummin et al., 2017), and are both widely feared and
heavily persecuted when located by the general public.
While there were 2,048 reported copperhead envenoma-
tions in the US in 2016 (Gummin et al., 2017), the over-
whelming majority of these envenomations (94%) were
either of a moderate or lower health-risk and there were
zero reported fatalities (Gummin et al., 2017).
With the continued and rapid expansion of urban-
ized areas across the copperhead’s range, especially in the
Southeastern US, where copperheads are still abundant,
the number of copperhead-human interactions is likely
to increase in the future. erefore, an understanding of
the anti-predatory behavior of copperheads may be used
to dispel misinformation, inform the public about the
behavior of this common and widespread venomous spe-
cies, and potentially serve to mitigate the negative conse-
quences of future human-snake encounters.
e aim of the present research is to examine the
anti-predatory behavior of the Eastern copperhead when
contacted by a potential human predator. Based on opti-
mality theory, we predict that copperheads will rely on
crypsis to avoid predation and will very rarely resort to
defensive anti-predatory tactics.
MATERIALS AND METHODS
Our study areas (n = 10) were dispersed throughout the
state of Maryland, a small state located in the mid-Atlantic
region of the US, and included a variety of habitats within each
of the state’s physiographic provinces. Maryland is comprised
of six physiographic provinces, the Atlantic Continental Shelf
Province, the Coastal Plain Province, the Piedmont Plateau
Province, the Blue Ridge Province, the Ridge and Valley Prov-
ince, and the Appalachian Plateau Province (Reger and Cleaves,
2002). Copperheads are widely distributed across Maryland
and occupy dierent habitats within these physiographic prov-
inces (e.g., bottomland swamps, rocky stream banks, south
facing slopes) across the state. e location of each site was
non-random, with study sites chosen based on prior distribu-
tion records collected through the Maryland Amphibian and
Reptile Atlas (Cunningham and Nadrowicz, 2018) or historical
localities gathered from Harris (1975). All encounters occurred
within the state of Maryland. Searches were conducted dur-
ing the copperhead’s active season, from 01 May 2017 to 01
November 2017, and again from 01 May 2018 to 01 November

33
Anti-predatory behavior of Eastern copperheads
2018. e snakes were located by visually searching each study
site by foot (Karns, 1986; Gibbons and Dorcas, 2002). In gen-
eral, snakes were found in areas adjacent to wintering den sites
with a large amount of adjacent cover in the form of rock crev-
ices and piles. Once a snake was visually located, the body posi-
tion of each individual, either coiled or extended, was recorded
prior to any further approach (Shine et al., 2000; Glaudas et al.,
2005). Since body surface temperature can play a role in defen-
sive behavior (Arnold and Bennett, 1984), we used a Ryobi Tek4
non-contact infrared digital thermometer (Ryobi, Chicago, IL,
USA) to record body temperature at three dierent locations
on the body (head, mid-section, and cloaca) from a distance of
~2 m and then averaged these values together (Garrick, 2008).
Ambient environmental temperature was recorded by extract-
ing local weather data from the nearest weather station using
the Weather Underground mobile application soware (v5.11.9,
TWC Product and Technology, Atlanta, GA) from the Nation-
al Weather Service, operating under the National Oceanic and
Atmospheric Administration (2018).
Once located, snakes had 1) an apparatus with a boot
attached placed directly adjacent to the snake to simulate a
possible human interaction while actively hiking (Gibbons and
Dorcas, 2002; Shine et al., 2002). Aer the initial approach and
rst trial, the snake then had 2) the apparatus placed gently
on top of it (to simulate accidental contact with a hiker; Gib-
bons and Dorcas, 2002). Finally, the snake was 3) grabbed and
picked up using a pair of snake tongs covered with a leather
glove to simulate a human hand (Gibbons and Dorcas, 2002;
Glaudas, 2004; Glaudas et al., 2005; Maritz 2012). A previous
study showed that a human hand elicits a strong anti-predatory
response, suggesting that faux gloved hand might elicit a similar
anti-predatory response (Herzog et al., 1989). Each stage of the
test (1-3) was carried out for 20 seconds and was videotaped
using a digital video camera (to allow post hoc analysis of the
defensive response).
During each phase, the observers recorded the defensive
behavior of the snake from the anterior end. Behaviors were cat-
egorized into four separate categories during each stage of the
experiment (eeing, tail vibrating, feigning a strike, and striking;
Gibbons and Dorcas 2002) to represent escalating levels of anti-
predatory responses. A feigned strike was classied as a lunge
forward without any discernible opening of the mouth. To test
the eect of human activity, environmental temperature, snake’s
body temperature, and the snake’s initial posture on anti-preda-
tory behavior, we categorized each snake’s response across trials
into one ordered value based on their most defensive response
to any of the trials (no-response [0], eeing [1], benign anti-
predatory response [2; tail vibrating], or defensive anti-predato-
ry response [3; feigning a strike or striking]). To test for asso-
ciations between ambient and body temperatures and behavior
we used an ANOVA. Both environmental temperature and the
snake’s body temperature were normally distributed (Shapiro-
Wilk W Test, W = 0.94 and 0.97 respectively). To test for associ-
ations between initial body condition and anti-predatory behav-
ior we used a Mann-Whitney U-Test. All statistical analyses were
conducted in JMP Pro (v14, SAS Institute Inc., Cary, NC).
We did not collect and individually mark snakes since it
would have been impossible to collect many of the snakes that
rapidly ed into adjacent cover (e.g., deep rock crevices, den
sites, heavy vegetation) in a manner that did not harm the
snakes or lead to the potential envenomation of the research-
ers. Additionally, since contact prior to the trials would have
biased behavior, marking could not have been performed prior
to the initiation of the trials. To help prevent “double-testing”
of the same snake, integument patterns (specically the darker
“hourglass” bands that may have been thin or wide, uneven,
broken on the dorsal side, etc.) were used as a basis for individ-
ual recognition and were supplemented by recordings of scale
abnormalities (Carlstrom and Edelstam, 1946; Shine et al., 1988;
Moon, et al., 2004). Post-hoc visual photo comparison between
each individual snake was conducted to remove any duplicate
trials. In total, we removed one snake trial from all analysis
aer post-hoc comparison conrmed that it had been tested
during a prior sampling period.
RESULTS
In total, we recorded encounters with 69 snakes
across all 10 sites (Fig. 1). Of these 69 snakes, 15 escaped
immediately upon discovery without performing any
other anti-predatory behavior and were not available
for any further trials. During the initial approach, one
snake performed tail vibrating before eeing, one snake
performed tail vibrating and a feigned strike before ee-
ing, and one snake attempted a strike. Aer accounting
for these 18 snakes, 52 snakes remained for further tri-
als. For a summary of the responses to each of the indi-
vidual trials (stepped next to (N = 52), stepped on (n =
33), and picked up (n = 14)), see Fig. 2. In total across
all trials, ve snakes displayed tail-vibrating behavior and
one exhibited a feigned strike followed by eeing (Fig. 2).
Across all trials, we recorded only two instances of strik-
ing (3% of all snakes).
ere was no relationship between snake anti-preda-
tory behavior and either ambient temperature (ANOVA:
F3,65, P = 0.92) or snake body temperature (ANOVA: F3,62,
P = 0.45). Similarly, there was no dierence in anti-pred-
atory behavior between snakes that were initially coiled
or extended (U = 255, P = 0.496). us, across all con-
ditions snakes showed similarly low percentages of anti-
predatory behavior.
DISCUSSION
Overall, our results provide evidence to support the
hypothesis that copperheads respond to potential preda-
tors in a manner consistent with their cryptic patterning.
Specically, copperheads are more likely to either remain
in crypsis or ee in the presence of a human rather than
display defensive behavior. Across the various trials of

34 Andrew Adams et alii
Fig. 1. Geographic distribution of the study sites across the state of Maryland. Each study site is represented by a pie chart with the binned
behavioral responses from all individuals at that site.
Fig. 2. Responses of copperheads to four increasing threat levels in a hierarchical anti-predatory trial (Found, Stepped Next To, Stepped On,
Picked Up).

35
Anti-predatory behavior of Eastern copperheads
the study, 93% of the snakes ed when we approached or
made physical contact with them. Furthermore, a higher
proportion of snakes (6%, n = 4) displayed no response
to any of our interactions (including being picked up)
than those snakes that struck during one of the trials
(3%, n = 2). While the proportion of strikes was low,
these results mirror the ndings of other studies exam-
ining pit-vipers’ responses to humans and consistently
demonstrate that despite the public’s perception of these
species as being dangerous and aggressive, that Pope
(1958) was correct when claiming that snakes are “rst
cowards, then bluers, and last of all, warriors.”
To examine how dierent intrinsic and extrinsic fac-
tors inuenced anti-predatory response, we analyzed the
eect of the initial body posture and body temperature of
each individual, and ambient environmental temperature
on anti-predatory responses. While we did not collect
individuals to gather morphometric data, the extremely
low prevalence of snake strikes makes it highly unlikely
that any eect of sex or size class on a snake’s anti-pred-
atory response would have been detected. However, with
a larger sample size, dierences in anti-predatory behav-
ior based on various intrinsic or extrinsic factors may be
detected. e published literature on the anti-predatory
behavior of snakes is full of conicting results regarding
the role of intrinsic and extrinsic factors on anti-preda-
tory behaviors both between and among species (Shine
et al., 2000; Roth and Johnson, 2004). Unfortunately, our
work does little to elucidate the dierences between these
conicting studies, except perhaps to further emphasize
that dierences in evolutionary history may be prohibi-
tive when attempting to produce general models of anti-
predatory behavior in snakes.
While for obvious safety reasons we were unable
to approach the snakes with an exposed hand or fore-
arm, other studies have also used a gloved apparatus to
simulate the human hand (Gibbons and Dorcas, 2002;
Glaudas 2004; Glaudas et al., 2005). While it is possible
that the dierence in temperature between the gloved
apparatus and a human hand may have modied the
anti-predatory behavior of the copperheads due to their
heat-sensing capabilities, no study has yet assessed the
importance of thermal cues in the modication of anti-
predatory behavior in free-ranging pit-vipers. Since no
studies have examined the eect of predator temperature
on anti-predatory behavior, examining the literature on
the inuence of temperature on predatory behavior may
be instructive. However, in the only eld studies conduct-
ed to this point examining the importance of thermal
cues on predatory behavior, Shine and Sun (2003) found
that while adult snakes were more likely to strike at
warmer objects, temperature was not a predictor of juve-
nile strikes, and Schra et al. (2018) found that absolute
temperature was not an important predictor of predation
attempts.
e public perception of venomous snakes as aggres-
sive and dangerous leads to a suite of problems for the
conservation of viperid species (see Seigel and Mullin,
2009 for an overview). Most notable among these issues
are the large organized round-ups that may lead to local-
ized extirpation of rattlesnakes (Adams et al., 1994; Fitch,
1998; Burghardt et al., 2009) and the lack of resources
that are made available for habitat protection or manage-
ment of these species (Seigel and Mullin, 2009). While
some studies provide cautionary tales about the poten-
tial backring of educational material (Ho and Maple,
1982), it is clear that increasing the public’s positive per-
ception of snakes will be a necessary component of any
long-term conservation plan (Seigel and Mullin, 2009).
More recent studies have shown that well designed edu-
cation programs focusing on biodiversity conservation,
the ecological role or snakes, or the use of antivenom for
medicinal use can improve feelings and attitudes about
snakes (Murphy and Xanten, 2007; Markwell and Cush-
ing, 2009). As part of this public outreach and education,
providing examples demonstrating the docile nature of
most venomous species may convince some individuals
to support legislation to prevent the organized killings
that persist to this day.
e results of this research provide previously una-
vailable information to inform the public of the docile
nature of copperheads and potentially assuage fears sur-
rounding the perceived aggressive nature of viperid spe-
cies. ese striking results should prove useful in con-
vincing the proportion of the public that is still impres-
sionable of the copperheads’ benign nature and may
result in an increase in positive public perception. Future
conservation of imperiled viperid species may hinge on
the ability of scientists to persuade policy makers and
the public of the importance and docile nature of these
species (Seigel and Mullin, 2009). is study provides
further evidence that common venomous species are
not aggressive and rely on striking only as a last resort.
As Charas (1677) noted over 300 years ago, “e viper is
taken by many for an image of malice and cruelty; but in
reality, she is guilty of no such thing”.
ACKNOWLEDGEMENT
We would like to thank M. Addicks, C. Auth, H.
Deery, B. Durkin, M. Gacheny, R. Hamilton, J. Hansen,
V. Lannen, R. Mady, J. Marlow, A. Rodriguez, G. Ross, K.
Stenta, M. Szymanski, and J. Wimmer for their valuable

36 Andrew Adams et alii
assistance in the eld during data collection. C. Searcy, S.
Clements, C. Mothes, D. McKnight, and R. Mady assisted
with manuscript revisions and provided statistical guid-
ance. S. Smith was a critical component of the permitting
process. All work was conducted under Maryland State
Department of Natural Resources Permit # 56452, and
in accordance with ASIH/HL/SSAR Guidelines for use
of Live Amphibians and Reptiles in Field Research. e
authors declare no conict of interest.
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