(1) An insect is an unwanted, odd, intrusive, spookily proportioned, often strikingly eerie hiking partner you suddenly discover has joined you while you are otherwise contentedly tromping down a trail, trying to enjoy yourself.
You discover one of these at your shoulder, or biting your neck, or crawling up your leg, or trying to burrow into your nose, in the same sort of way that you've found some other unexpected hiking partners doing, but those others you could just punch in the face and be done with it.
Insects are harder to deal with.
One reason for this is that many insects hate to leave home alone, so they approach you in squadrons (the flying ones), or in divisions (the crawly ones). If so, you find that you suddenly have dozens of the little buggers to deal with. In addition to this, many insects are armored and hard to neutralize (the crawly ones), or if they are not the crawly ones, then they form flying clouds and carry some annoyingly effective weaponry at the ready, such as pokers, stingers, or nippy-nippers.
Some of the crawly ones also have their own implements of war, and though these ground-based guys are easier to hit with a counter-strike than the often teensy-tiny flying ones, their scaly shells make them tougher to put out of commission, even at those rare times when you can manage to score a direct hit. One upside, however, is that insects can be surprisingly entertaining when introduced to a roaring fire, even in small numbers.
(2) An insect is a life-form that cannot be appeased or negotiated with, one existing below the threshold of rationality, driven only by the most basic instincts to drink your blood, to bite holes in your hide, to lay eggs in you, or to make you insane by buzzing in circles around your head for hours on end, never approaching too close until you finally let down your guard, whereupon it swoops in and makes off with a chunk of your flesh. Insects are easily identifiable because they always have way too many legs and have those weird little solid-state eyes that see in all directions at once without moving, but despite that they never ever manage to notice the other people with you, only you. Sweet, tasty you.
(3) Someone you do not like, even if they are crunchy and taste good.
(4) A person fascinated by Instagram or other modern electronic perversions. This sort always carries a cell phone, extra battery power, stereo speakers and cabling, says things like "ur" and "lol" and "rofl" and "ymmv", broadcasts music across the landscape at every opportunity, and is unaccountably attracted to you, and will find you, and will set up immediately next to you, surely and inevitably, even if you have crawled half a mile off-trail to camp under a bush so you can have the privacy and quiet you so desperately need. Easy to detect, instantly identifiable, infinitely irritating, yet devilishly hard to kill.
(5) Our food future, after all else has withered away. At such time we shall all become insectarians, and though some of us will die gagging during the cut-over, it will be a sort of revenge, will it not?