Cribellate Orb Weaver spiders are an interesting for several reasons, but what primarily makes this taxonomic family intersting is that they are non-venomous. Instead they kill they prey by constricting it by weaving a fine thread of silk of over 140 metres several thousands times around it. I belive they wrap it so tightly that the force causes it’s insides to burst outwards.
Now it strikes me as odd of how the ancestor of the Cribellate Orb Weavers would have evolved this seemingly very high-energy cost method of killing it’s prey when it would’ve previously had the venomous bite in which to kill it’s prey.
Now I know that I may well be being far too simplistic and relying on cursory appearance rather than a real evaluation of the hunting strategies employed by spiders. Butr what are the current theories on how this behaviour evolved?
Don’t know about existing theories, but it could start easily with a spider that disabled and bound it’s prey in a less severe manner, then evolved the tight binding method. Maybe this all happened after the spider’s ancestors lost their venom. Some form of binding would be valuable to survival once venom is no longer available. From the other side of the change, losing venom is no big deal once you can kill your prey that way. Not all prey succumbs to venom that easily, and not all venom is extremely effective.
If the ancestral condition was being venomous, then there was most likely some evolutionary reason for the loss of venom. It is useful to consider what those possible reasons might be.
This article presents an evolutionary hypothesis for the evolution of wrapping and the subsequent loss of poison glands in Cribellate Orb Weavers (Uloboridae), which is a bit too complex for me to go into here.
As others have said - it doesn’t have to be the ‘best’ - it just has to work.
Also you need to avoid the trap of looking at the present world as if we are at some kind of ‘end point’ of evolution where every life form should be optimally evolved to survive and reproduce. You have to assume that many of the plants and animals alive today are going down evolutionary paths that will come to dead ends for one reason or another.
However, these kinds of non-answers are not particularly useful to questions such as this. There are reasons for the evolution of these traits, and it is useful to hypothesize how they developed, as in the article I linked to.
Yes, efficiency isn’t the be all and end all a sometimes downright inefficient qualities can evolve, for example due to sexual selection.
However this is clearly evolved behaviour as you have a venomous ancestor that has evolved a quite complex (or reasonably complex for an arthropod) behaviour to kill it’s prey and has lost it’s venom as an inirect result. There must be a selection pressure for this to happen.