Pricilla i don't disagree that there are probably alot fewer butterflies now for enviromental reasons but also have you considered that maybe you haven't seen them because you have less time/oppurtunity. When you're younger you notice all these things and you have time to laze around and just observe, long summer days etc etc but as you get older, more responsibilities, work, less time, rushing around trying to get things done. it's amazing how much you can miss.
I lived in a city in England for years - never thought of really looking around, nature etc. i moved back here and out to the country and love watching the sun rising, setting, changing seasons etc which i had forgotten about. I notice also when with young child you notice so much more because they draw your attention to it. Without meaning to sound philosophical/ sentimental i really feel the poem which begins "What is life if full of care we have no time to stand and stare" is even more appropriate today when so many of us work in cities and offices and are more detacted from nature than our ancestors.