Monarch butterflies are rather famous. They're colourful and beautiful and migrate for thousands of miles between Mexico and Canada. Experiments in 1999 showed that they were poisoned by GM Bt corn pollen which had been sprinkled on milkweed leaves, their favourite food. Later studies showed that most of the Bt corn varieties seemed to be quite safe for butterflies because they produced far less of the toxin than the plants that had been used in the experiments. The highly toxic variety — which made up to 40 times more poison than others that are available — was taken off the market.
But it does show that people have to keep checking for possible bad effects of GMOs.