MICE, CALCIUM, AND MOLTING

Shed exuvia of an adult, female Brachypelma emilia.

AN ILLOGICAL CARRYOVER A few enthusiasts prefer to feed their tarantulas "gut loaded" crickets or crickets dusted with a vitamin and mineral supplement for whatever reason. And, we've seen comments on the Internet forums stating quite unequivocally that this is a bad practice for the same reason as feeding mice or other vertebrates to a tarantula, and with the same lack of supporting evidence, and in the face of the same contradictory arguments.

To begin, you need to understand that this myth has been ricocheting around the Internet mailing lists and forums since at least the early 1990s. It's a relatively old one that refuses to die. We don't know where its origins lie, or who may have been responsible for starting it.

Our guess is that several decades ago someone fed a mouse to their tarantula. For a number of reasons we strongly suspect it was a Theraphosa blondi. Sometime thereafter the tarantula died during an unsuccessful molt. This is not too surprising because most wild caught T. blondi die shortly after being imported anyway, being notoriously difficult to keep. It would almost certainly have been a wild caught adult, because in that time frame they were only extremely rarely bred in captivity and babies were very uncommon or non-existent.

Our hero immediately blamed the death of the tarantula on its eating the mouse because the only remarkable thing that stood out in their mind was the struggle between the tarantula and the mouse. The assumption was made, and the myth sprang into being like a big, ugly toadstool!

Either our hero or someone else who heard the seminal myth elaborated on the hypothesis by noting the fact that mice have a calcium endoskeleton whereas normal tarantula food (i.e., crickets) does not. Isn't it then blatantly obvious that the calcium in the mouse's skeleton was the cause of the bad molt and the ultimate death of the T. blondi? The myth went viral, and now we're repeatedly assaulted by it as the King's truth

So, what's the truth? There were serious shortcomings in this myth from the every beginning.

• First, the skeletons of young mice are mostly cartilage. They're only beginning to become calcified at that point in time, so vast amounts of calcium aren't available.


• And, tarantulas' precursors have been eating anything that came their way since long before mammals or even vertebrates were even a twinkle in the Grand Creator's eye. Over the last third of a billion years that vertebrate prey has been available, it requires a huge leap of negative intellect to imagine that arachnids/spiders/tarantulas wouldn't have evolved an efficient way of dealing with any calcium issues. Or, gone extinct.


• And, our hero is completely ignoring the fact that both Sam Marshall (Tarantulas and Other Arachnids) and Rick C. West (both respected arachnologists and field investigators who've actually been to South America to study T. blondi) have reported that in their wild habitat T. blondi subsisted on a diet very rich in forest floor amphibians. That translates into a natural diet rich in calcium. With no obvious untoward affects.


• And, our hero is completely ignoring the fact that there are tarantulas dying every day from bad molts, that never have had a mouse in their lives.


• And lastly, our hero is completely ignoring the fact that there are a truly impressive number of enthusiasts who routinely feed their larger and giant tarantulas on young mice and never, ever experience any molting problems.

Few of us feed mice to our tarantulas as a sole diet. Mice tend to be expensive to buy and troublesome to breed. Hence, mice are most commonly used only by a relatively small portion of enthusiasts, and usually only for exceptionally large tarantulas. But even then, if feeding mice or otherwise overloading a tarantula with calcium had any profound, recognizable effect, surely the results would be a lot more obvious, consistent, and testable than the mere conjecture we hear.

Scratch that myth. There's no believable evidence to support it, and a lot of lines of reasoning, if not hard evidence to refute it. It's busted!

But nothing about tarantulas is ever that simple. They've simply had far to much time to elaborate and fine tune their lives!

When feeding mice to tarantulas it is important to feed only very, VERY young mice, babies or slightly older, that have not yet learned to use their teeth as weapons. It is considered very bad form in the arachnoculture hobby to risk a valued and valuable pet in a fight to the death with a larger mouse. It is interesting to note, however, that small or baby frozen mice are available from some pet shops (look for those that cater to the exotic pets trade), and there are frequent reports of tarantulas quickly learning to eat them once they are thawed and reach room temperature. (But, NEVER attempt to microwave a mouse unless you have some perverse necessity to either clean up a very messy microwave, or buy a new one!)

What? You say you forgot to take a frozen mouse out of the freezer before you went to school or work this morning? No problem! Take one out now and merely throw it into a cup of hot tap water until it's completely thawed.

There is one possibly valid criticism of feeding mice to tarantulas: Tarantulas fed regularly on mice always become obese. The fact is that there is no data on whether obesity has any bad effects on tarantulas (as there is in humans). We simply don't know. And, we can't make an educated guess based on other animals because spiders in general and tarantulas in particular are so different, even bizarre. There are lots of other instances where they have violated the rules followed by other creatures on Earth, and seem to be surviving with panache anyway! The only thing we think we know for sure is that a really obese tarantula can't be all that comfortable with all that bulk and weight, just like we.

And, the next question is, "What's different about a mouse that they make tarantulas so obese so fast?" The answer is, "We don't know." If we had to fabricate a story we'd guess it has something to do with the composition of the proteins and lipids in mice compared to insects. Or, their relative abundances per gram of body weight, perhaps. But, don't quote us on that. It's just conjecture.

Is there any real justification for feeding your tarantula a mouse? Perhaps. Perhaps not.

Occasionally, enthusiasts acquire fully grown giant tarantulas (e.g., T. blondi - goliath birdeater tarantulas, or Lasiodora parahybana -Brazilian salmon tarantulas) that refuse smaller food like crickets or even cockroaches. We found, for instance, that our giant tarantulas could become very spoiled in favour of mice very fast. Like me in a chocolate store! For them, small mice may be the only option, like it or not.

Some enthusiasts are concerned that their tarantulas may require a more varied diet for various reasons, and choose to feed an occasional baby mouse to their tarantula as a dietary supplement. But, there is virtually no hard data on the dietary needs of tarantulas in general, or known dietary deficiency diseases among them with the single exception of feeding solely fruit flies to baby tarantulas. So, there is still some question about the necessity or efficacy of feeding mice to most tarantulas.

There are also some ethical concerns voiced over the practice of feeding live mice to tarantulas. That topic will not be discussed further here. Each enthusiast must come to their own decision on the issue.

SO, NOW YOU KNOW BETTER. AND WE FULLY EXPECT YOU TO CARRY THE TRUE WORD HELD HIGH WHENEVER YOU HEAR A REFERENCE TO MICE, CALCIUM, AND SOMEONE'S MOLTING TARANTULA.

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This page was initially created on 2013-March-10.
The last revision occurred on 2013-July-04.