If the quantity of small Redbacks is low, another option for a hatchling supplement is taking the just the tails from adult Redbacks. The adults regenerate with no negative side effects.
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Small tadpoles work sometimes.
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" I'll have to try fish "
Precautionary note.. Don't use fish very often and never use them that have been frozen more than a month. (Thiaminase)
Good Luck

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Regards, Bill McGighan