One day in July of 2013, I decided to head to a local nature preserve and see what there was to see. I grabbed my camera, laced up my boots and hopped in the Jeep.
July’s hot temperatures tend to depress wildlife activity, but because it had been raining on and off since the previous afternoon, I felt like I had a pretty good chance of finding a few critters.
I arrived at the preserve and set off down the trail. Unbeknownst to me, a tiny snake was lurking on the forest floor, ready to change the ways in which I thought about snakes and storms. It probably even made me a better skeptic.
And that is always a good thing.
I said I went out with the intention of “seeing what there was to see,” but this isn’t completely honest. I had a specific quarry in mind.
I am fond of the vast majority of the animals running through southeastern forests, from the red-backed salamanders and patent leather beetles lurking under decaying logs to the redheaded woodpeckers and blue jays singing from the canopy.
Nevertheless, we all have our favorites, and on this day, I was looking for one of my favorite local species — the copperhead.
Copperheads are relatively small pit vipers; the largest males may slightly exceed 4 feet in length, but most adults are in the 2- to 3-foot range. The young, which are normally born in the late summer or early fall, are tiny and measure about 8 to 12 inches in length.
Highly adaptable animals, copperheads will eat virtually anything they can. This means that in addition to standard snake fare, such as rodents, lizards and frogs, copperheads also prey on cicadas, caterpillars, salamanders, other snakes and birds.
Copperheads actively prowl for food at times, but often, they simply curl up in the leaf litter and wait for prey to walk by. Clad in some of the most effective camouflage in the animal kingdom, they are well adapted for such tactics.
The young even bear sulfur-yellow tail tips, which they will wiggle in a manner suggestive of a caterpillar or worm. When a passing frog or lizard spots the yummy treat and moves in, the tables are turned. The forest floor springs to life, and the prey finds itself staring down the business end of a hungry pit viper.
Copperhead venom normally produces relatively mild symptoms in humans and deaths from their bites are almost non-existent with competent medical care. But the venom will ruin your day, as it causes great pain, swelling and tissue damage; so, bites are definitely best avoided. I actually witnessed a young lady get bitten by a copperhead in this very park a few years before. She made it through the incident with no long-term repercussions, but her parents were faced with a six-digit medical bill.
In the southern United States, snake encounters usually decrease in frequency once summer is in full swing; the midday temperatures are simply too hot, so many snakes shift their activity patterns or enter a period of pseudo-dormancy. Accordingly, a July morning is not exactly the ideal time to find a copperhead crawling through the forest.
However, the previous night’s storm had soaked the area thoroughly, and snakes often become active during and after storms or heavy rains. At least, that is what conventional wisdom suggests.
This tendency for snakes to become active in conjunction with rainy weather appears in plenty of popular literature and educated people from zookeepers to PhDs treat this premise as a basic fact. My own experiences supported the contention as well. While I never collected or analyzed any data on the subject, I have found snakes crossing roads, trails and driveways during heavy rains dozens of times.
The potential reasons that would explain the change in activity are legion. Rain cools the forest, giving snakes the chance a temporary reprieve from sweltering summer temperatures. It may also flood the subterranean retreats of some snakes, forcing them to seek out new accommodations. Others may become active because their prey become more active in the rain.
Snakes become active in response to rainy weather, so I felt I had a really good shot at finding a snake – hopefully, a copperhead.
The problem is, when you look into the research conducted on snake activity vis-à-vis weather, the data does not always support the presumption that rain influences their behavior. Some researchers have found that the species they study do become more active during or after rainfall, but others have found that rain has no effect on the subjects of their studies.
For example, sea kraits — some of the most interesting (and toxic) snakes in the world — clearly alter their behavior in the face of rain.
Unlike most true sea snakes, who spend their entire lives in the ocean, sea kraits are amphibious. They spend most of their time hiding from predators amid terrestrial rock crevices and periodically venturing out into the ocean to capture their own prey.
The snakes remain relatively safe while hiding in their refuges or swimming in the water (where their banded color pattern may serve to repel sharks), but they are rather vulnerable when traveling between the two. Accordingly, as explained by Xavier Bonnet and Francois Brischoux in a 2008 study, published in Austral Ecology, sea kraits spend as little time as possible in the deadly zone between their hidden retreats and the sanctuary of the sea.
However, other factors help shape the behavioral patterns of these snakes as well. Despite being supremely adapted for a life spent in salt water, sea kraits require fresh water for drinking.
Surrounded in all directions by the salty water of the ocean, sea kraits remain hydrated by consuming fresh rainwater. When it rains, freshwater pools amid the numerous rock crevices and depressions along the shoreline, thereby providing a lifeline for sea kraits. However, because the hot tropical sun evaporates the water quickly and splashing waves contaminate the pools with salt, the sea kraits do not have very long to drink the water.
Therefore, when it rains, the sea kraits throw caution to the wind, emerge from their holes and begin slurping up the water like mad. They often adopt unusual postures to help harvest as much fresh water as possible and continue to drink until they are satiated.
This proves that at least some snakes alter their activity based on rain, but what about more “normal” snakes, who live in places with plentiful water?
Otavio A. V. Marques, Andre Eterovic and Whaldener Endo investigated this very question at the end of the 20th century when they examined the snakes living in the coastal rainforests of southeastern Brazil. Publishing their results in Amphibia-Reptilia, the team found that six of the species native to their study area did become more active during the rainy season. This provides some additional corroboration of the hypothesis that some species become more active during rain.
But, you may be thinking, rain does not exist in a vacuum, it causes several other changes in the environment. How do the humidity and temperature changes alter the behavior of snakes?
To address that issue, M. Ermelinda Oliveira began teasing apart the influence of rain and the factors associated with it, in 2001. Interestingly, Oliveira found that the activity patterns of lance head vipers living in the Amazon Basin, were very significantly correlated with rain, while temperature and humidity played almost no role in their behavior.
We now have at least three peer-reviewed studies that have documented snakes becoming more active during rainy weather. Along with the consensus among snake keepers, it appears that the hypothesis is strong.
Except that it isn’t.
I neglected to mention one important bit of data produced by the Marques, et al study. In addition to the six snake species the researchers documented becoming more active during the rainy season, one species was encountered more frequently in the dry season, and four others were equally active in both the wet and dry seasons.
Plenty of other studies have also produced evidence at odds with the hypothesis that snakes become more active in wet weather.
A 2005 study of Australian tiger snakes by H. Butler, B. Malone and N. Clemann revealed that rainfall did not affect their activities in any significant way. In fact, the snakes were more active on sunny days than they were cloudy days.
Dennis K. Wasko and Mahmood Sasa studied terciopelos living in Costa Rica and found that rainfall did not influence their behavior. Publishing their results in a 2009 issue of Biotropica, the authors found that terciopelos (also called fer-de-lances) acted normally in all conditions except “extremely heavy rains”.
But the most important study (to my mind) was carried out by G. P. Brown and R. Shine, who tried to really get to the bottom of the relationship between snakes and weather. While the researchers did find some subtle trends in their research subjects – water pythons activity levels varied with the amount of moonlight – they found that “…standard weather variables (temperature, humidity, precipitation, moonlight, atmospheric pressure) are surprisingly poor at predicting the numbers of individuals and species encountered during standardized surveys.’
Looking at the available evidence, it seems that while some snakes become more active in rainy weather, others become less active or fail to alter their behavior in any meaningful way when it rains. Why then, do so many people that are wise in the ways of snakes, believe that snakes become more active in rainy weather when the evidence suggests behavioral patterns vary widely among different species?
In my case, the reasons are pretty clear: Over-generalization and confirmation bias.
The statement “snakes become more active during rainy weather” is both simultaneously right and wrong; it is true in some cases, and false in others.
While they form a natural group and all spring from a common ancestor, snakes are a diverse group of organisms, who have evolved in response to a variety of selective pressures. Accordingly, the 3,000-odd living species respond to rain in many different ways. Some species do become more active in rainy weather, but others exhibit the opposite trend. Still others don’t seem to care one way or the other.
Confirmation bias is the tendency for people to embrace evidence that supports their hypothesis while ignoring any evidence that conflicts with their previously drawn conclusions. I certainly fell victim to it in this case, and I will fall victim to it again in the future. We all do; we’re only human.
Essentially, I remembered all of the times I encountered a snake when it was raining, but ignored all those other times when it was raining, but I did not encounter a snake.
It is also likely that I read and retained more literature supporting the correlation than things that stood at odds with the contention. I thought that snakes became more active in rainy weather, so I subconsciously favored the information that confirmed this.
It was not until I started writing about this very forest outing that I tried to find a reference to back up the fact. However, upon perusing the literature, it quickly became apparent that a relationship between snakes and rain was far more complicated than I originally thought.
So, as you move forward, be mindful of the effects confirmation bias can have on your thoughts and actions.
But be sure you don’t step on your confirmation bias because it can pack a wallop.
I was hardly 20 minutes into the hike when I saw this little beast slithering across the trail, about 100 yards in front of me. The trail was mostly comprised of wet, dark mulch, which contrasted starkly with the pretty gray and beige snake, but it was the movement of the snake that caught my eye.
After completing an inspired rendition of the “I found a copperhead!” dance, I regained my composure and began snapping as many photos as I could. After filling a memory card with far too many identical photos, I scooted the little bugger off the trail with a stick. This particular animal looked too small to be a yearling, so I imagine he/she was only a few weeks old at best. This would seem to be a little early for copperheads to be giving birth, but 2013’s winter was very mild and spring arrived quite early, potentially giving this snake’s mother enough degree-days to complete the developmental process a bit early.
Chance encounters like this will drive you crazy. If I had had another cup of coffee before leaving the house or caught a few more green lights on my way to the forest, I probably would not have encountered the little snake.
I have yet to find any rigorous studies examining the relationship between copperheads and rainy weather, but after recognizing the roles over-generalization and confirmation bias played in my prior thinking, I will try to avoid them in the future. I certainly fall victim to these traps in the future, but hopefully, I will stumble into them less frequently.