tegus are usually more aggressive during a feed response or when young as they feel threatened by larger creatures, not to say that I haven't seen an aggressive adult, but it seems more common...i have found that overcoming a few bites is usually the best solution with the younger ones, and yeah you will bleed, but you can wear gloves to prevent any sort of pain and anguish, i just think its better to go without, i have a 8-10 month old Argentine and he is in a feeding frenzy constantly, his growth has been almost 7 inches in the past 2 months...he was aquired in the fall and went into hibernation 2 weeks after purchase. I was kind of upset as i knew when he came out he wouldn't be to accustomed to my presence, it took nearly 6 months of waiting to see him rise from his long sleep. I was quite suprised at just how emaciated he became, as all of his tail fat was gone and his hips were showing slightly under the skin...i provided water for 2 days and fed him scrambled eggs to start him off on solids, he eats about 4 dozen King MW's and 6 mice a week now, with the occasional scrambled eggs enriched with vitamins and calcium powder. He gets real frenzied and recognizes the hemostats as food as well as his bowls, so cleaning and feeding can be a 2 person job sometimes. Once he is full he becomes much more docile, but is still flighty, and takes some time to calm down in my hands. An animal such as this has a calculated response when they feel threatened, it's instinct, this is the way they are and part of being a responsible herper is knowing how to deal with such responses....they are definitely a handful at times...do not get discouraged, simply diagnose the problems and solve them and he will mellow with age.
the things to remember in herp husbandry when trying to figure out strange behavior in herps is simple
environment (enclosures, heat, light, season)
diet!!!
maturity/sexual maturity
overall health (vet checkups, parasites)
these terms are broad but they narrow down the problems, an aggressive tegu could be caused by all of these...another household pet such as a dog or cat can even make them act really out of character...an interesting experiment would be to keep a tegu for years inside, then in a secure manner and in a proper enclosure let it sit outside for a day or two in some real sunlight, then try to handle it.....you will see aggression of the highest form..
-craig
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Craig