The Spider Mutation and the
Associated "Wobble Head" Syndrome

By now, most people who have been involved with ball pythons for any length of time are familiar with what has come to be known as "wobble heads".
For a long time this was the dirty little secret of the spider mutation. With prices at the time ranging in excess of $10,000 each, no one wanted to talk about it. As prices fell though, and more and more people began working with the morph, it finally became common knowledge that there was something often not right about a spider.

I feel that since I myself am producing spiders that it is also my responsibility to ensure my customers are aware of the condition and what I think it means. Rather than repeating myself to each potential customer individually, I decided to write this page and use it as a reference, and hopefully it might be useful to others as well as those who are just learning about it.

First I'll explain the condition itself. The wobble head syndrome is a variable loss of motor control, primarily of the head and neck. It is variable in that it manifests itself to varying degrees between individuals.
Some spiders have no wobble at all, some show some head tremors when in a high state of alertness such as when hunting, some individuals show irregular head movements whenever they move. In some extreme cases, which are not that common, it can make it difficult for them to right themselves, and all but inhibit any form of normal locomotion.
To make matters even more confusing, some individuals initially show no signs of a wobble, but go on to develop it at several months of age. Some have been seen to be the opposite, early in life having some degree of motor control loss and then growing out of it so to speak. Others have developed it after a while only to lose it again later.

The question is what causes it? Unfortunately no one knows for sure. Currently all we have are theories and what I will relate here is mine, which I think is shared by the larger portion of the ball python breeding community.

There are two schools of thought concerning the "wobble heads". One is that it is some sort of additional genetic defect that is separate from the spider gene but was introduced early in the production of the morph. Being a separate gene, those who subscribe to this line of thought believe that the condition can be eliminated from spiders by selectively breeding only those individuals who do not display the condition.
The other school of thought is that the loss of motor control is genetically linked to the spider gene, an unfortunate side effect of the mutation that can not be eliminated due to the genetic linkage.

I subscribe to the latter theory and I have what I feel to be strong evidence to support that position. Let's look at some facts about spiders and the wobble head condition.

  • Spiders which do not demonstrate any sign of the condition have been shown many times to produce offspring that do.
  • Conversely, specimens which do wobble, have been shown to produce offspring which show no signs of the condition at all.
  • Spiders, being a dominant trait with no super form are now probably the single most outcrossed mutation we work with today.
  • There has never to my knowledge been a normal sibling in a spider clutch that demonstrated the wobble head condition, it has only been seen in spiders and combo mutations in which the spider gene is a component. (I have seen it suggested once that there has been, but there is no supporting evidence to the claim, and no specimens have been shown publicly.)

Now let's look at these facts and what they mean.

1. The fact that spiders which do not wobble have produced spiders that do, and vice versa, strongly suggests that all spiders in fact carry the same defect which causes it. Since the condition when present is extremely variable in the degree in which it affects the snake, it is my opinion that in some cases it is present in such a mild degree that it simply isn't manifested at all. Since some of the offspring of these individuals do express the condition, it therefore must be true that the parent carried the defect even though it showed no signs of the condition at all.

2. Some have suggested that an additional mutated gene was introduced early in the development of the morph and gained a strong presence in the gene pool during the period when breeders were inbreeding in search of the homozygous super form of the mutation.
There are a couple of problems I have with this theory which make it impossible for me to accept at this time. First, if it was indeed a separate gene not inherently associated with the spider gene, then it behaves in a manner which cannot be explained by the current genetic principles with which I am familiar. It is not dominant because a specimen which wobbles can produce offspring which do not. It is not recessive, because a spider with the wobble when bred to a pure normal can produce offspring which wobble as well.
Furthermore there is the fact that the condition only affects spiders, not their normal siblings. This is the strongest point for me, if it was a completely separate gene, then why are normal siblings never affected by it?

The fact is we still understand very little about genetics, especially in reptiles, compared to all there is to know about them. We can only speculate as to what the actual cause is and what its true relation is to the spider mutation.
But each person will have to determine for himself whether the condition is acceptable at all and to what degree if it is. I myself have no issue with some minor wobbling, knowing that in all probability it will show up in any breeding project at some point regardless of the condition of the founder individual. If I produced a seriously impaired individual, I would choose to put it down rather than subject it to a lower quality of life, and at the same time I wouldn't have a problem buying a spider with some minor wobbling if I liked it and including it in my breeding group.

So in short, it is my belief that the "wobble head" syndrome is unavoidably linked genetically to the spider trait and as a result, it will never be eliminated through selective breeding. I would quickly add however, that that is only a theory. I would genuinely like to be proven wrong one day and see the condition completely eliminated. At this time though I just can't see anything associated with the condition to give me cause for hope that it will be. There are those who have determined to try, and I hope they prove me and the others who share my opinions wrong.

Regardless it will take quite a long time and several generations before a given group can be claimed to be wobble free.
As I see it, the best we can hope for is discovering the intensity of the condition to be also genetically determined and therefore be able to breed for the lesser severity. It will take many years I believe to gain any real understanding of what is actually going on with these spiders, if we ever understand it at all. It may be that the condition and its severity cannot be controlled and we will always have the occasional extreme case. It is my opinion that the extreme cases should not be allowed to live, let alone breed because the worst of them really cannot have a quality life.
At this point though I feel secure in saying that if you work with spiders, you will at some point produce one that wobbles, regardless of whether your original founding animals have it or not, and minor manifestations are just going to have to be accepted as an unavoidable side effect of this beautiful mutation.