When Atul Awasthi bit into his muesli bar during his lunch break the last thing he was expecting was a caterpillar crawling out.

The Auckland scientist was on a lunch break from an animal pharmaceuticals company in East Tamaki when the caterpillar wriggled out between the chocolate-coated nuts on his Tasti nut bar.

The New Zealand Herald reports that Mr Awasthi immediately went to the toilet to throw up. "I was horrified."

Experts say the moths, which are commonly found in household pantries, are almost impossible to avoid and are not harmful to humans.

But Mr Awasthi feels that Tasti, which apologised and sent him vouchers for two free packets of the muesli bars, were "blase", and did not take his complaint seriously enough.

Tasti, a Te Atatu-based company which produces muesli bars and cereals, said it had done everything in its power to prevent the Indian meal moth from getting into stock. Marketing director Adrian Cook said the "nasty little creature" was a known worldwide problem.