What makes a species more defensive/aggressive?

[tarandrewla]

I know that there are some rather snappy B. smithi, and some rather laid back species that are known to be defensive, but for the most part each species tend to fit into their general description.

What makes this so? Genetics I guess, but why? How can it be that certain members of the Theraphosidae family vary so greatly? I just have never been able to wrap my brain around how temperament is wired into an animal, though I do understand how physical characteristics eventually evolve in order to adapt to an outside environment.

 

[Chris_Skeleton]

Why does it surprise you that members of different genera act differently?

Look at dogs, different breeds behave differently and they are all one species. Considering that, it's not that surprising comparing spiders that aren't even the same species.

 

[tarandrewla]

Why does it surprise you.

I'm not saying it surprises me. I'm just curious as to why different tarantulas react so variably, seemingly according to their species.

 

[curiousme]

Temperament can be affected by many things, but personally I feel that enclosure size has alot to do with. We have no Ts that I would describe as overly defensive, or even defensive really; but all are kept in larger than necessary enclosures for their size. I can't believe that we beat the odds 24 times and just have well behaved spiders. People that speak up about their defensive Ts often are doing more utilitarian compact housing in my experience of reading on here. Other factors can of course play roles in the temperament, but that is my personal opinion on the matter.

 

[AphonopelmaTX]

It is my belief that aggressive and defensive behavior is determined by the hostility of the environment in which an organism live. By hostility, I mean the pressure to compete for resources and to defend itself from predators. For instance, just about everything in the Amazon jungle is either aggressive or has adaptions to defend itself really well (i.e. venom) due to the shear amount of organisms who are all fighting to stay alive and in close proximity to each other. Same as in the rainforests of South East Asia, Africa, etc. and even in baron habitats like the Australian outback. When it comes to tarantulas specifically, it's known that those taxa with urticating bristles use them as a primary defense instead of biting first and those without bite first because that's the only defense they have. It seems that the taxa with urticating bristles rely on them so much, that they don't even bite attacking animals that are not effected by them or don't have a severe reaction making them appear docile.

- Lonnie

 

[tarandrewla]

It seems that the taxa with urticating bristles rely on them so much, that they don't even bite attacking animals that are not effected by them or don't have a severe reaction making them appear docile.

You make a fantastic point. If you think about it, if a New World tarantula flicked it's bristles the same amount of time an Old World species used it's fangs, that would make a B. smithi just as defensive/aggressive as an OW T.

Yikes! I'll never be able to look at my B. emilia the same way again!

 

[LirvA]

evolution imo

 

[Kaimetsu]

You make a fantastic point. If you think about it, if a New World tarantula flicked it's bristles the same amount of time an Old World species used it's fangs, that would make a B. smithi just as defensive/aggressive as an OW T.

Yikes! I'll never be able to look at my B. emilia the same way again!

This is exactly what i've always assumed. A common ancestor of all new world tarantulas, having evolved an alternative and highly effective self defense(urticating hairs), no longer needed to be highly defensive and no longer needed potent venom against big mammals, so most of them lost their potency against big mammals.

Theres another possibility that occured to me recently although i think this is less likely. Humans and other hominids have lived in Africa and Asia side by side with old world tarantulas for over a million years, while humans have only inhabited the new world for around thirteen thousand years (some recent evidence suggests much longer but i don't think more than like forty thousand.) Is it possible that old world tarantulas have evolved higher venom potency against humans as a defense against predation/harassment by humans? I suppose a good way to test this would be to test old world T venom against other big mammals and see if theres much difference.

Anyways just some ideas i've been tossing around in my head.

EDIT: If there are any evolutionary biologists or entomologists on the forum who can provide some input on this it would be cool, this is a topic that interests me alot.

 

[Malhavoc's]

I know that there are some rather snappy B. smithi, and some rather laid back species that are known to be defensive, but for the most part each species tend to fit into their general description.

What makes this so? Genetics I guess, but why? How can it be that certain members of the Theraphosidae family vary so greatly? I just have never been able to wrap my brain around how temperament is wired into an animal, though I do understand how physical characteristics eventually evolve in order to adapt to an outside environment.

I am shocked in my skimming I didnt see this answer given.

A creature responds with what it has to handle the situation. If you look over the various Defensive behaviors of tarantulas you will find "Old World" tarantulas to be far more likely to bite you- It has been said this is primarly because it is their only defense. "New world" Tarantulas have specialized hairs that they coat their lair, flick. and otherwise use to harrass any would be attacker. They do not need to bite when the hairs are their own deterant to being eaten.

Also another nice comparison.
Burrowing species are far more likely to bite then aboreal species. Burrowers are often traped and or cornered when stressed/handled in our care, they have no where to go and nothing to do. Aboreal species are far more likely to 'flee' unless they feel cornored. Alot of bites I have heard or seen is after the tarantula has already tried to escape once twice or three times.

Brightly coloured tarantulas (OBTS) who again cornor themselves in enmass webbing, use their flamboyant colours and vibrant displays before going into a biting frenzy (usualy) And again, when given the option of running they will.

*** This is all my speculation after keeping many species over the years.


I stand corrected, a more thorough reading of the thread shows that AphonopelmaTX already touched upon this subject.

 

[Merfolk]

I assumed that different predatores triggered the developement of differnt mechanismes. Like urticating hair should be more efficient when the predators brings its nose close to the prey(like a racoon) rather than simply grabs and squishes like a monkey. In the later case, a quick and painful bite is the only way out for the spider...

 

[0siris]

You also have to take into account that tarantulas can't see very well and gather most of their information from around them by means of sensing vibrations. There's no surefire way of telling which vibration is food and which vibration is danger. I think certain species, namely those that live in more hostile environments have simply learned to develop a "better safe than sorry" attitude. Exactly as AphonopelmaTX stated.