"An epigram is but a feeble thing - With straw in tail, stuck there by way of sting"

This quote by William Cowper is a humorous way of describing an epigram. An epigram is a brief, amusing stating or poem, frequently with a creative twist at the end. Cowper is recommending that an epigram is not extremely effective, which the creative twist at the end is like a "sting" - a weak one at that. He compares it to a "straw in tail" - a little, insignificant thing. This quote is an amusing method of explaining the limitations of an epigram. It implies that while an epigram can be smart and amusing, it is not an effective tool for conveying a message. Cowper is suggesting that an epigram is a feeble thing, and that its smart twist is not enough to make it really efficient.