One of the things that surprises many people is just how slowly tarantulas actually grow. Unlike many of the arthropods crawling around our gardens, tarantulas don’t reach maturity in a matter of weeks or even months. Tarantulas can take several years to go from spiderling to adult spider.
In a Nutshell
It’s very difficult to give a ballpark figure for how fast tarantulas grow. This is because there is a surprising diversity of tarantula species known. Some quite simply grow faster than others.
Environmental factors can affect the situation: tarantulas kept warmer or given more food tend to grow faster. The genders can also affect growth rates – male tarantulas may grow faster than their female siblings in some cases. All this means that a “one rule” situation doesn’t really work.
Instead, it’s safer to give broad figures, appreciating that there will be some variation.
Most tarantulas will grow from spiderling to adult in 2-5 years when properly fed.
Typically males will mature sooner, at around 2 years of age, while females may take another year or two to reach maturity.
It is worth noting that female tarantulas can keep growing with every molt, even after reaching maturity, so the biggest female tarantulas tend to be the oldest.
How Often Do Tarantulas Molt?
In order to grow a tarantula must slough their tough exoskeleton. This process known as “ecdysis” enables the tarantula to reveal a new, larger skin beneath the old one.
A huge range of factors can affect how often a tarantula molts. Some factors to consider are:
Species in Question
Some tarantulas grow faster than others. I’ve had some tarantulas like the Mexican Fire Leg (Brachypelma boehmei) and the King Baboon (Pelinobius muticus) go 18 months or even 2 years between molts on some occasion.
Some other species, such as many Psalmopoeus species, seem to be constantly molting and will therefore reach maturity much sooner.
Age/Size of the Tarantula
Smaller or younger tarantulas tend to molt more frequently than larger or older specimens.
For faster growing species it is not unusual for them to molt every 3 months or so as spiderlings and juveniles.
As they get larger, however, this space between molts begins to extend, until at maturity a once-per-year molt is typical.
Availability of Food
The more food a tarantula is given, the faster it will grow, and so the more often it will molt. This is sometimes known as “power feeding” – providing an almost never-ending supply of food to a tarantula hoping to encourage it to mature sooner.
Warmer temperatures typically result in faster growth rates and hence more molts.
I’ve noticed in my own collection that whenever we get a heatwave in summer suddenly a huge number of my tarantulas molt. The difference in temperature in my tarantula room may only be a few degrees, but it’s enough to kick-off a molting process in a lot of spiders.
The Impact of Lifestyle on Speed of Growth
With so many species of tarantula in the hobby it’s hardly surprising that there is a lot of diversity in how quickly they grow.
Broadly speaking there are two alternative lifestyles that tarantulas take. Some are fast growing but relatively short-lived. The others are far more long-lived but slower growing. Of course there is still a fair amount of diversity here.
If you buy a fast-growing tarantula you need to accept that your tarantula probably won’t live as long as some other species. Equally, the frustration of rearing a slow-growing tarantula can be tempered by the realisation that you’ll probably have the specimen for decades to come yet (assuming it’s a female).
Examples of Fast Growing Tarantulas
At this point it’s probably useful to highlight some fast growing tarantula species in case that’s what you’re looking for.
Males may mature in 2 years, sometimes even as little as 18 months. And females typically aren’t too far behind when fed liberally.
As you’ll see, many are hobby favorites, and due to their fast rates of growth tend to be bred frequently and reasonably-priced to purchase, even at quite large sizes.
Orange Baboon (Pterinochilus murinus) – Always a popular choice among more experienced keepers. Super-easy to rear as they like a dry environment with good ventilation. Their fiery attitude means they’re probably not the most suitable spider for beginners. I’ve had males reach maturity easily in 18-24 months.
Indian Ornamentals (Poecilotheria genus) – Pretty much all members of the Poecilotheria genus are fast-growing and can reach maturity in just a couple of years. Having said that I have personally found Poecilotheria metallica seems rather slower-growing than others like P. regalis, P. ornata and P. refulilata.
Salmon Pink Birdeater (Lasiodora parahybana) – This big, impressive tarantula which is clothed in beautiful pink hairs can put on mind-blowing growth spurts. Seriously, if you buy one take two photos a year apart and see just how much size it’s put on. Even better, as Salmon Pink Birdeaters can reach 8-9” across the legs they just keep going, getting bigger and bigger for years to come!
Brazilian White Knee (Acanthoscurria geniculata) – This is a tarantula that always seems to have an appetite. I’ve tested it, offering a suitably-sized locust to a specimen every day. It ate every time until it finally went off food before a molt. Understandably a tarantula that will eat daily will find it easy to grow fast.
Psalmopoeus Genus – There are a number of popular members of the Psalmopoeus genus including the Venzuelan Suntiger (Psalmopoeus irminia) and the Trinidad Chevron (Psalmopoeus cambridgei). They’re all beautiful in my opinion, and even a spiderling can reach a legspan of several inches within a year to eighteen months.
Examples of Slow Growing Tarantulas
At the other end of the spectrum are tarantulas that grow slowly but are notably more long-lived. In some of these I’ve waited 4 years or more for a male to reach maturity, with frequent periods of 6 months or more between molts even as juveniles.
These slow rates of growth can mean that while they’re reasonably priced to buy as a spiderling the price increases at a breakneck speed as the tarantula grows. This is simply a function of how much time and effort has gone into rearing it to that point.
Brachypelma Genus – Brachypelma tarantulas, which include the well-known Mexican Red Knee (Brachypelma hamorii), are recognised as being some of the longest-lived tarantulas around. Females have been known to live over 20 years on occasion. As you might expect, therefore, they can be quite slow-growing.
Grammostola Genus – While there is some variability within this genus, most of the commonly-kept Grammostola tarantulas are very slow growing. This includes Grammostola rosea, G pulchra and G pulchripes. Prepare to be the very model of patience. At the time of writing I have a juvenile Grammostola pulchripes that hasn’t molted for 8 months, when many of the fast-growing species I keep would have molted twice or more in that time period.
Brazilian Blue (Pterinopelma sazimai) – Have you ever wondered why the Brazilian Blue is so commonly and cheaply found as a spiderling, but that larger specimens can be eye-wateringly expensive? Yep, it’s because of how slow they grow. I’ve been rearing some P. sazimai alongside a range of other species – such as Psalmopoeus irminia – and the Brazilian Blues are a fraction of the size of the others. Indeed, roughly 15 months since I bought them as newly-hatched spiderlings they measure a legspan of only 3-4cm.
Chilean Flame (Hommeoma chilensis) – I am rearing a number of spiderlings of this species at present. They were purchased over a year ago and still measure only a centimeter or so in legspan. In fact, I’d say that after 25 years of rearing tarantulas it is H chilensis that is the slowest-growing species I’ve ever kept.
Conclusion: How Fast Do Tarantulas Grow?
Tarantulas grow a lot more slowly than many people realize, typically taking 2 -5 years to reach maturity. During that time they may change their skin anything from every 2-3 months to up to 6 months or more. The bigger the tarantula gets, the greater the period of time between molts.
Even within tarantulas there is some variability, meaning that some species grow much faster than others. Additionally, male tarantulas, those kept warmer and fed more typically grow much faster than a female kept at cooler temperatures and fed less often.
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