The origin of the concepts that your pet tarantula must have some special, optimal ambient temperature, and that it shouldn't change beyond some closely confined margin of error are lost in history. We do know that two other related hobbies, tropical aquarium fish and reptiles, both have very good reasons for maintaining proper temperatures for their pets. And, we know that many people who keep tropical fish or pet reptiles also graduate or gravitate to keeping tarantulas. Perhaps the temperature myth with tarantulas is just a carryover from those hobbies.
Regardless, here's the real story.
Any animal that either doesn't control it's body temperature at all, or that only controls it by behavioral means is called a poikilotherm. In the vernacular, we say they are cold blooded. All tarantulas are poikilotherms. They don't expend (there are those of us who would prefer the term "waste") vast amounts of food energy to maintain an artificially high body temperature. And when they're not actively doing something, they idle along at so slow a rate that it's sometimes difficult to tell if they're still alive at all.
It also means that they come from the factory with a built-in ability to operate effectively across a truly remarkable range of body temperatures. They barely notice the ambient temperature until it approaches physiological extremes, perhaps somewhere below 60° F (16° C) for a low and somewhere above 100° F (38° C) at the maximum. Low ambient temperatures that tarantulas can survive for brief periods (perhaps overnight, for example), even though they won't be operational, vary from near freezing for many temperate zone and montane species, to the 50°s F (low "teens" C) for the tropical species. Maximal high body temperatures for any tarantula seem to lie somewhere above 110° F (43° C).
However, having said that, we are not aware of any formal studies addressing the issues of extreme temperature tolerance in tarantulas. The limits stated here are either the result of personal experience on the author's part or anecdotal information from other enthusiasts. Thus, these extremes should only be considered as guidelines, and the prudent enthusiast should do everything possible to avoid exposing their prized pets to such extremes.
The whole homeotherm/poikilotherm schema presented here is vastly oversimplified. Anyone who gives even a moment's thought should immediately be very suspicious!
Your first clue that this may not be quite correct might be that with something on the order of 10 million different kinds of living organisms on this planet, absolutely nothing is going to be this simple, this cut and dried. This seems just too good to be true. There are in fact all kinds of variations and exceptions. To illustrate the point, we itemize a few of them here.
This entire discussion is being oversimplified in order to keep it readable. Those who are more interested in further reading are encouraged to search the Internet for these terms and any other search strings that present themselves.
Any animal that maintains an elevated, more or less constant body temperature by internal, physiological means is called a homeotherm, warm blooded in the vernacular. As mammals, humans are homeotherms. Yes, we also control our body temperature by behavioral means (e.g., we move in or out of sunlight for instance, and dress warmer in winter and lighter in summer), but that is merely a secondary, perhaps "legacy" means of temperature control inherited from our far distant ancestors. Under most circumstances we produce all needed heat internally, and as often as not our bigger concern is disposing of excess heat. To this end, we spend a lot of time, effort, and money avoiding extremes of temperature and dressing for the weather. Almost all of our temperature issues where tarantulas are concerned are strongly skewed by this prejudice.
Homeothermic species like humans cannot tolerate anywhere near so wide a range of body temperatures as the poikilotherms like tarantulas. An important portion of our enzyme systems (the workhorses of all our metabolic processes) are so fragile that we become deathly ill if our body temperature exceeds or drops below a very narrow margin for error around 98.6° F (37° C).
Among humans, for instance, a body temperature above 100° or 101° F (38° C) is considered by the medical profession to be a fever, and we begin to die at a temperature above 110 F (43° C). By contrast, the medical profession considers a temperature below 95° F (35° C) to be too low a body temperature, or hypothermia. We're in trouble outside of a narrow 6° F (3.3° C) span!
We can suffer kidney failure, heart failure, and experience convulsions as our finely tuned, delicate, central nervous system begins to fail. Eventually we fail to breathe. Allowing our core temperature to go too high or too low without intense medical monitoring and support is not good! And, we need only mention the words fever or hypothermia to prompt an almost instantaneous response if not outright panic.
As a survival strategy, we come from the factory with a built-in hypersensitivity for detecting when our surroundings become too cold or too hot, feeling extremely uncomfortable when this happens. We have electric blankets, heated floors, forced air furnaces, and air conditioned homes, automobiles, businesses, office buildings, even air conditioned dog houses, all controlled by thermostats to prevent our surrounding air temperature from varying more than a degree or two either way of our preferred temperature.
And, both our "comfort zone" and "survival zone" are much, much narrower than those of a tarantula.
We are so caught up in our own prejudices that the simple fact that the overwhelming majority of other living things on this planet are not homeotherms flies right over our heads, and that an often widely varying body temperature is normal. (See the sidebar Minority Report.)
In fact, not only is a widely varying body temperature normal, but in many cases it's required! We know for a fact that many organisms entrain their annual behavioral and hormonal cycles to annual swings in temperature (and day length), and we believe that those fluctuations influence tarantulas as well. One of the more glaring examples would be Grammostola rosea, the Chilean rose tarantula.
So, here we have our first clue that tarantulas may be able to tolerate a much wider spread and variation in temperature than we had first been led to believe. In fact, if they couldn't, we might be quite surprised!
In the wild, tarantulas are exposed to an astonishingly wide spectrum of temperatures.
There are several species of tarantulas that display remarkable endurances for cold. For instance, there is an as yet unnamed species of tarantula (probably belonging to the genus Hapalotremus) that lives at 14,700' (4500 m) above sea level in the Cordillera Vilcanota of the Peruvian Andes. It's reportedly the highest living tarantula on the planet, and hunts actively in the daytime when it can benefit from the much needed heat of the sun. However, even in mid summer that close to the equator the nighttime temperature drops below freezing.
This tarantula's ability to withstand extreme cold is as yet unexplained. Because the soil at that elevation, even so near the equator, is almost surely permafrost or close to it, it is unlikely that deep burrows could save it from freezing to death, ruling out that hypothesis. More likely, this tarantula contains a high concentration of some bio-antifreeze in its hemolymph that prevents freezing. But this is all conjecture. None of this has been verified by research.
This presumption is supported by circumstantial evidence in other animals from Antarctic fish to a wide assortment of insects and a number of other cases as well. However, each kind or small category of animal seems to have evolved its own bio-antifreeze independently of the others. Some of these animals use exotic sugars, others use glycols, still others may use specially customized proteins.
Science has described approximately 5,500 mammals and 10,000 bird species on planet Earth. These two groups of animals comprise the overwhelming majority of all warm blooded (homeothermic) animals, a total of about 15,500 species.
By comparison, almost all scientists estimate that there are probably between 2 and 30 million different kinds of living animals on planet Earth (both poikilothermic and homeothermic kinds). We'll pick a number that makes the following math easy: 10 million. (Yes, we are almost surely wrong. But, we're doing this for illustrative purposes only, so we claim the right to a little "poetic license".)
Now we do the math. If we divide the number of homeotherms by the number of all living animals on Earth (15,500/10,000,000) and multiply by 100 we get the percentage of warm blooded animals to all other living organisms. And, that number is only 0.155%.
(An additional but unrelated consideration is how this tarantula manages to gain enough oxygen to survive in the rarified air at such altitudes in the light of tarantulas' putatively inefficient respiratory systems. But, this is a subject for a different time and place.)
Because this remarkable tarantula lives in one of the most inaccessible regions of the planet, and its domain is protected by an extended patchwork of "farmlets" controlled by chieftains, each of whom must be appeased before proceeding on to the next farmlet, the probability of our acquiring any of these for the hobby is almost non-existent. And, acquiring living specimens for research is only slightly less impossible. Don't hold your breath!
(A tip of the ol' hat and our many thanks to Rick C. West for supplying us with the information about this enigmatic species.)
A little closer to home, a species of North American tarantula (Aphonopelma iodius) lives on the mountain plateaus north of Logan, Utah, USA at elevations of approximately 5,000' (1525 m). This may be the most northerly species of tarantula in the world. It apparently survives the entire winter in deep burrows plugged with soil and leaves, buried under deep snow. Presumably, the snow acts as a cold but very effective insulator to prevent their freezing during protracted cold snaps. Do they also possess bio-antifreezes that prevent freezing? We don't know.
Tarantulas enduring the high extremes of temperature are nonetheless remarkable. Species inhabiting the Death Valley region of California (another species of Aphonopelma), the Afar Triangle in Ethiopia (several species of Ischnocolus and Loxoptygus), and Al `Aziziya, Libya (Ischnocolus tripolitanus) among other hot places routinely survive air temperatures well above 120° F (49° C) for weeks or months on end by hunkering down in their burrows to escape the heat.
Even the more "normal" tarantulas of southern Texas (e.g., Aphonopelma anax and A. moderatum) must frequently endure air temperatures in the 110° F (43° C) range for weeks on end in summer, And, these authors and many others have witnessed these tarantulas eating and mating (rarely at the same time!) at temperatures in the 100°+ F (38°+ C) range.
But, the foregoing are only the extremes. The majority of tarantulas not living in the tropical lowlands also endure, even revel in wide, daily and seasonal fluctuations in temperature.
For instance, Aphonopelma hentzi in Oklahoma (arguably the archetypal American tarantula) will be exposed to daytime air temperatures in the high 90s to low hundreds Fahrenheit (about 35° to 43° C) in summer. But, in early morning the air temperature may drop into the low 70s F (low to mid 20s C) or even lower. That would be a daily air temperature change of approximately 20° to 30° F (11° to 16° C).
And, wintertime lows in these same regions often drop well below freezing (e.g., 25° F or -4° C). Thus, these tarantulas survive quite nicely in the face of an annual temperature fluctuation of 75° F (42° C)!
And, these authors and many other enthusiasts have witnessed wild, Texas tarantulas (see above) actively hunting at temperatures as low as 63° F (17° C), and basking in the heat of the early morning sun at even lower temperatures.
We have heard people remark that, "Oh, that's just in the USA. African tarantulas are different." But in fact, while the Kalahari Desert may reach temperatures approaching 122° F (50° C) in their summer, it may also drop to well below freezing on a winter's evening. Some of our favorite African tarantulas are native to the Kalahari and surrounding area!
An important argument here is that these are generally only AIR temperatures, that the tarantulas normally hunker down in the bottom of their burrows during these extremes and seldom or never experience such temperatures. And, of course, if this weren't at least partly true all these tarantulas would have been baked or frozen to death eons ago.
But, those burrows are not perfect insulators, and are often open to the air at their tops. So, heated or chilled air does have ample opportunity to seep in and affect the tarantula. And yes, many tarantulas plug their burrows during long bouts of inclement weather, but seldom do so for very short term periods of instability. Thus, they are exposed to SOME temperature changes even when hiding at the bottoms of their burrows.
One must also accept that when daytime temperatures reach into the low 100° F (38+° C) range, surface soil temperatures go much higher in direct sunlight. And, over a period of weeks to months, all but the very deepest burrows will eventually heat (or cool in winter) to temperatures approximating air temperature. While it may help, living at the bottom of a burrow is no guarantee against extremes of temperature.
A number or tarantulas are native to deep, lowland, rain forests where the daily and seasonal temperature fluctuations are minimal. The enthusiast's first assumption is that these would be very sensitive to temperatures outside some well defined range much like most tropical fish. Nothing could be farther from the truth. This topic will be expanded below.
(Note: While these authors have heard of studies done on the temperature fluctuations in tarantulas' burrows, we haven't been able to find published reports of the data. If any readers know of such published works we would appreciate being told about them, or sent copies (PDFs or otherwise) of them. See Communications, below.)
Thus, even without knowing about the underlying theory, with a little simple observation and common sense we would be led to believe that most, if not all tarantulas are capable of tolerating some remarkably wide range of temperatures, certainly wider than what we humans could tolerate.
So indeed, variety is really the spice of life!
The creatures we call tarantulas (spiders of the family Theraphosidae) have been known by humans for many millennia. And, a few of them had been formally described and named some time before Linnaeus published the tenth edition of his Systema Naturae... in 1758. (The publication of that book is generally agreed to mark the beginning of the modern science of Taxonomy - the organized description and naming of all living organisms on Earth. Select here for free, downloadable copies of volume one and volume two.)
We are quite certain that curious little boys have been keeping tarantulas as pets for millennia. And equally certainly that curious older folk, natural historians, have also been keeping them, studying them, describing them, and naming them for hundreds of years. But, the astonishing thing is that no one had ever actually written a book on their natural history, biology, and care in captivity until Dr. William J. Baerg did so in 1958 with his landmark book, The Tarantula.
We mark the beginning of the arachnoculture hobby with the publication of Dr. Baerg's book. And thus, as this is written, the tarantula keeping hobby is less than 55 years old!
The simple fact is that EVERY care sheet, and an almost unbelievable proportion of postings on the Internet forums discuss temperature issues and their importance with tarantulas. Is temperature really all THAT important to captive tarantulas?
During the brief period of time that we have been keeping tarantulas as pets (see the sidebar "In the Beginning."), the hobby has gained no small experience with these enigmatic creatures. In those few decades thousands, perhaps tens of thousands of enthusiasts have kept hundreds of thousands, perhaps more than a million, tarantulas as pets. And, it is safe to assume that tarantulas as a group have thus been subjected to a truly awe-inspiring range of conditions during that time. Surprisingly, in spite of that, the majority of them survived for many years.
When all the reports of tarantula deaths are compiled, a curious fact surfaces. Of all the ways that tarantulas have found of dying or being killed in captivity (not arranged in any particular order) ...
... no one ever complains that their pet tarantula got too cold, got sick, and died!
(This, however, conveniently ignores an extremely small number of cases where tarantulas actually froze to death due to their owners' incompeitence.)
Even though EVERY care sheet, and an almost unbelievable proportion of postings on the Internet forums discuss temperature issues and their importance with tarantulas. Is temperature really all THAT important to captive tarantulas? Apparently not.
Even if you knew nothing of a tarantula's physiology, even if you knew nothing about their natural lives, the simple observation that they never seem to die in captivity from temperature related causes (baring actual cooking and freezing because of carelessness on their owners' parts) should raise a red flag about the importance of temperature in captive tarantulas' lives.
Thus, the underlying theory, direct field observations, and many years of practical experience by thousands of enthusiasts all allow us to make a general statement that tarantulas can survive and function efficiently within an unexpectedly wide range of temperatures.
The overwhelming preponderance of evidence points to one fact: Tarantulas don't seem to care a lot if their temperature varies a few degrees, or even more than just a few degrees, within a surprisingly wide operational temperature zone. It's apparently no big deal, at least from the tarantula's point of view. And there is scant or no evidence to the contrary.
So, contrary to popular belief by we fanatically prejudiced homeotherms, being a cold blooded animal is definitely NOT a disadvantage. And, judging from the data, it quite apparently has an abundance of distinct advantages. At the very least, one cannot argue with its success.
It would seem then, temperature vis-à-vis tarantulas is a red herring. Merely something else that we can stress over, buy thermometers and cage heaters for (and thereby stimulate the international economy), write up recommendations in our care sheets for, and hold extended discussions on the Internet forums about. But generally, if kept within reason, temperature is of no real importance.
And, what is "within reason?" We repeat ...
IF YOU DON'T HAVE TO WEAR A WOOL SWEATER OR A PARKA TO STAY WARM...
IF YOU DON'T HAVE TO RUN NAKED BECAUSE IT'S TOO HOT...
ANY TEMPERATURE YOU'RE COMFORTABLE AT WILL SUIT YOUR TARANTULA JUST FINE.
WE ARE THE FRAGILE LIFE FORM, NOT THE TARANTULAS!
But that doesn't mean that they are completely unaffected by their temperature. Far from it! Here we discuss how tarantulas DO interact with temperature.
As hinted above, tarantulas practice a behavioral form of thermoregulation. They have been observed in cool mornings at their burrow's entrances sunning themselves, a practice well known to be used by many creatures to warm in the heat of the early morning's sun.
And, there are many references by enthusiasts of captive tarantulas preferentially staying near cage heaters in cool rooms or after cool evenings.
This immediately begs the question, "Then, why do we NOT openly propound the use of cage heaters in tarantula care?" (In fact, we strongly speak against them!) There are a number of reasons.
Having said all this, there is always the rare instance where artificial heat is desired or necessary. Several such situations come to mind.
If you really have to, NEED TO, artificially control your Tarantula's cage temperature there are several strategies you might use.
DO NOT DO THIS!
YOU'VE BEEN WARNED!
GROWTH RATE AND MATURITY
Enthusiasts have known for decades that there is some correlation between temperature, feeding, growth rate, and age of maturation in tarantulas. But, beyond that basic concept, the exact rules are only poorly understood. The reason for this is that it's a bad experiment.
Just so we're all reading off the same page...
Perhaps it would be useful to examine these three points in a little detail. If an experiment is run with only one independent variable, perhaps changing only the temperature in our case, and ensuring that all other conditions are constant, then we can say that any deviation from the original conditions is almost surely due to the independent variable, i.e., changing temperature.
If, however, you change two variables at the same time the best you can say is that any changes were due to either one or the other, or to both variables. It will be most difficult if not impossible to use the results of your experiment to predict the results of another experiment. If the results differed, you could never be sure exactly why except in a very general, indeterminate way. And, if they agreed, you could never be sure it wasn't purely coincidence - the result of two different conditions interfering with each others' effects.
An additional problem involves the confusion between which dependent variable you're measuring, growth rate or maturation age. This may seem like a trivial concern to some, but there is a big though subtle difference, and unless this is defined at the outset an otherwise good experiment might go for naught.
So, what's the difference? Growth rate is merely the rate at which body mass or some other measurable quantity changes with time. For instance, we gain in height, we gain weight, our arm length increases, etc. Note that we are restricting our consideration to only measurable changes in size. Growth is a quantitative change.
Sexual maturation involves certain anatomical, physiological, and biochemical changes that result in an organism's ability to reproduce. And, of course, maturation age is the length of time from some benchmark (usually but not necessarily birth or hatching) until sexual maturation is achieved. These are aspects, even extensions of development from embryo to death. While growth and age of maturation are often closely related, growth is not always necessary or important to either the process of maturation or the age of maturation. While the age of maturation may be a measurable, quantitative character, maturation per se is primarily a qualitative characteristic.
The uninitiated enthusiast may assume that growth and age of sexual maturation march hand in hand in tarantulas, as they more or less do in humans. But, this is not necessarily so with poikilotherms (e.g., tarantulas), and the two must ever be sorted out as distinct entities in these considerations. Failure to do so has produced much confusion and discord.
The last reason why most of our anecdotal reports are bad experiments is that almost everybody who has explored these phenomena has either failed to control or accurately record the changes in the variables they were testing, failed to control other variables besides feeding and temperature (e.g., day length, sex, species), or failed to report the details of their experiment at all (e.g., making some vague anecdotal reference). Nearly everyone is using a different set of circumstances. And, when all their results are collected and an attempt is made to correlate their data, only very vague tendencies seem to appear and there are frequent, confounding contradictions.
Remember that these all seem to be general rules, not hard and fast laws. The Independent Variable is mentioned first, and the Dependent Variable last. Lastly, it is presumed that all other conditions are kept constant (i.e., "locked in").
Further, it seems that all these effects are greatest immediately after escaping the eggsac (i.e., dispersal), and diminish as the tarantulas age and grow, ceasing entirely with adult males upon their ultimate molt, and slowing to an almost imperceptible rate with near-adult and adult females.
Two questions that have not been addressed at all by enthusiasts except by pure conjecture are -
Enthusiasts have learned to use the rules outlined above to selectively accelerate or retard the growth rates of their tarantulas. One aspect of this practice is called power feeding in the arachnoculture hobby. Power feeding may be defined as maintaining a tarantula at a slightly elevated temperature and feeding it excessively to accelerate its growth and maturation rates. It's generally used in only a few instances.
As mentioned above, the exact rules that govern the final growth rate of a tarantula are not well understood, and may be different for each kind. But, beyond the simple observation that a higher temperature and more food generally promotes faster growth in tarantulas, the issue becomes very muddy. It's by no means a universal dictum.
By way of example, and as noted above, power feeding some African species causes the males to mature much more quickly, but at a significantly smaller body size, the so-called "mature runts" mentioned above.
And, these authors were party to an instance where a male Brachypelma albopilosum that was power fed to the extreme grew to a quite respectable size and matured in only a few days more than nine months! And, this characteristic has been noted by others as well. (Five years or more is normal.)
Lastly, on at least one occasion on the Internet, an experienced and respected enthusiast seriously questioned whether power feeding really did promote a relatively faster maturation among males than among their corresponding sisters.
It would seem that the matter is far from settled.
While those tarantulas that are kept warmer will eat more, may grow faster or mature sooner, and may die more quickly, what happens if tarantulas are kept a little cooler and fed less?
Simple logic would lead one to assume that if males are kept cooler and fed less than their brothers from the same eggsac which are kept at higher temperatures and fed more, they would take longer to mature. Baerg (citation currently unavailable) even noted this with Aphonopelma hentzi, and a few anecdotal reports would seem to confirm this hypothesis, but there are not enough of them to permit an across-the-board declaration of fact.
One situation in which such a consideration would be important is the instance where only a very few eggsacs were available during only one season from a rare or rarely imported species. As the baby tarantulas from those eggsacs grew, the males would ordinarily mature one or two years before their sisters. That would make breeding that kind of tarantula impossible since the mature males would all have become too old or even died of old age before their sisters were mature.
And indeed, this author has heard unconfirmed reports of enthusiasts using the principle of "reverse power feeding" to selectively retard the growth of males so they could be bred to females of their same age.
There is one very important aspect of arachnoculture that depends heavily on bending the rules: breeding tarantulas. There are a few kinds of tarantulas that breed readily in captivity, Avicularia avicularia (Guyana pinktoe tarantula) and Brachypelma albopilosum (curlyhair tarantula) for instance. But, there are many tarantulas that have proven very difficult to breed in captivity, and enthusiasts are exploring these species' sensitivity to, or need for special conditions outside those recommended by the party line to promote breeding.
Hence, enthusiasts who are very successful at breeding tarantulas often make a practice of cooling their spiders to remarkably cool temperatures for several weeks to several months in winter to stimulate them to breed the following spring.
We admit that there are advanced enthusiasts who are trying to answer specific questions or achieve specific goals, who regularly bend or outright violate the guidelines suggested here. But, these are not rank novices "doing their own thing" out of ignorance. The "newbie" should follow the rules at first. Learning how to properly care for your newfound pet is the important goal for now. The time for experimenting will come later, after you've gained much experience, learned what little is already known, and can assess the risks and benefits of experimenting with your pets.
Relax! Take it easy. This is not an instantaneous hobby. It's a long term "getting to know you" sort of thing. There's plenty of time, perhaps a whole lifetime, to enjoy these phenomenal creatures.
Communicating with us is easy. Just select here.
Copyright © 2011, Stanley A. Schultz and Marguerite J. Schultz.
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This page was initially created on 2011-June-25.
The last revision occurred on 2013-April-02.