It is possible to cross breed tarantulas, but this is very much frowned upon within the tarantula keeping community.
Cross breeding is generally only possible between closely-related species.
The reproductive organs of tarantulas vary quite significantly in design. Furthermore, different species of tarantula have varying mating dances/calls. Therefore a distantly-related male may not be able to successfully calm a female from a different species before mating.
Examples of the importance of this closeness is the cross breeding that has occurred in the past between different Brachypelma tarantulas. In the distant past Brachypelma hamorii was “successfully” crossed with Brachypelma emilia, for example.
On the other hand, it is likely that a male Brachypelma hamorri introduced to an adult female Lasiodora parahybana will simply end up as dinner rather than romantic partner.
Why is Cross Breeding Tarantulas Bad?
Cross breeding tarantulas is frowned upon because it messes with the “pure” genetics of tarantula species.
Wild tarantulas are imported in limited numbers each year, and hobbyists become a repository of these rare creatures. Maintaining pure blood lines means these tarantulas can potentially be re-introduced in years to come if conditions are right and wild populations become damaged.
A cross bred tarantula, however, becomes useless for this purpose.
A further concern when it comes to cross breeding is that identifying tarantulas when they are small is very difficult indeed. Even larger specimens can cause issues with identification. One spiderling looks very much like another, quite frankly.
Cross breeding tarantulas is therefore also a concern when hobbyists may accidentally purchase a hybrid without even knowing that is the case. They may spend years lovingly rearing up the tarantula, never knowing the truth about the genetics of their spider.
The more of this cross breeding that occurs deliberately, therefore, the more likely it is to happen accidentally. A hobbyist may mate two “hybrid” specimens without even realizing it.
Accidental Cross Breeding
While it is fair to say that deliberate cross breeding of tarantulas very rarely happens these days, there are cases where cross breeding could occur by mistake. This is especially so in unidentified tarantulas, or those recently imported from a wide area.
There are concerns among experts that some of the tarantulas we have in captivity may have been incorrectly identified in the past. Or that when we think of as a single species, may actually comprise two or more species when spread over a larger area.
Of course, if you end up with an adult pair of tarantulas both bearing the same name then you might naturally think about breeding them. But of course if it turns out these specimens are actually different species then you will have taken part in cross breeding.
This is one reason why I personally don’t like to deal with “unidentified” tarantula species. When a tarantula has not been scientifically described, or identified by a capable expert, then you can never be 100% certain about their genetics.
Cross Breeding & Color Forms
A slightly more slippery question about cross breeding comes in the form of color forms. Some tarantulas may come in two or more colors, but are believed to be the same species.
The classic example is the Trinidad Olive tarantula – Neoholothele incei. This tarantula exists naturally in an attractive “olive” form but also as a “gold” form. Both look identical to the eye with the exception of the color.
Being the same species, these tarantulas will readily reproduce. The question is whether this is the right thing to do. Should we try to keep these colors separate, or is it acceptable to offer “hypo” offspring that contain a mixture of genes from both color forms?
I have yet to hear a definitive answer to this question, but I have seen some European breeders offering “mixed” offspring for sale without any hint of shame.
Perhaps, therefore, this is deemed not to be “cross breeding” at all by hobbyists.
How Much of a Problem is Cross Breeding Tarantulas?
Generally speaking the tarantula-keeping community is against cross breeding. It is very much frowned upon.
While there have been historical cases of deliberate hybridisation occurring, these days it seems the average tarantula keeper is unlikely to attempt it. As a result, deliberate cross breeding of tarantulas isn’t a major issue right now.
At the same time, as discussed, it isn’t always possible to know for certain that your tarantula is pure. This is especially so in smaller specimens. As a result it is worth buying tarantulas from reputable breeders who should have the knowledge and the ethics to avoid cross breeding tarantulas.