DEET is an ingredient in many types of insect repellent. I'm not sure, but I think Canada may have banned products containing more than a certain amount of DEET.

DEET is extremely effective against mosquitoes and flies, but it can be hazardous in more than small quantities. I had a Timex watch which had it's plastic face melted/corroded/whatever after I accidentally sprayed a DEET product on it while camping. Nasty stuff, but a necessary evil sometimes.