Canker worms, BTK, and what does it all mean?

So anyone who has been to the 'Peg knows we get a lot of skeeters and canker worms.
http://www.canada.com/globaltv/national/story.html?id=4ba96560-28cc-40e3-989b-3b037f464975
This year the worms are everywhere! I have trees around my apartment; and when I go to open my door to go inside: the door is covered. I hear from a pal that cankers are in Kansas as well. In plentitude.

Anyhow, they have been spraying with BTK. I know a few people who are strongly against the spraying. Honestly, I don't know much about it one way or another.

I am often watching, in my amateur way, how certain species will spike up during certain seasons, and others decline. Certain critters and plants, certain weather, seems to make it possible to predict which ones will be abundant the following year, and which other guys to look out for right now. etc. etc.

So I have a tonne of questions.

Does anyone know or have opinions on:
BTK. Is it safe? Is this something which I should put more thought into at all? Is it screwing up the system and does it poison other species....thoughts or experience with BTK?

What I've been pondering for a good while is......
What other species are in a spike while cankers are?
Why?
There must be some sense to high populations of cankers: what are they doing for the ecosystem and other critters, plants, soil, whathaveyou?

Also, does anyone have any suggestions in giving oneself a crash-course on ecology? What would be the best bet in learning about it: as a hobby?

thx