Out of all of them, poison ivy is the scariest to me. It looks a lot like a normal plant, and I heard it can last a YEAR, which is long compared to mosquito bites.
Edit: Thank you for clarifying that they don’t usually last a year.
I guess I’m afraid of some of the more dangerous viruses, bacteria, and parasites, although not enough so to give them much thought in daily life.
I get into poison ivy a couple times a month on average, but fortunately I’ve never had the rash last longer than a few days.
I would be afraid of most large predators - and quite a few large herbivores - if one came charging toward me, but it isn’t a “won’t go in the woods because of them” or “constantly looking over my shoulder” level of fear.
Some humans. Not so much the serial killers lurking in the shadows type, as the Elon Musks of this world. Most dangerous organisms of all, and the greatest threat we have ever faced.
I doubt it. I’ve never had it last more than a week, at the outside. It’s definitely annoying, but not scary. Best treatment: hot water, as hot as you can stand it without burning yourself.
House centipede.
Not necessarily scared but hyper aware, I would say
- Triatominae because of Chagas
- Aedes aegypti because having had dengue, I know to have it subsequently would be worse (mostly I worry for our son, whose dengue turned hemorrhagic)
But because I am aware of both of these, I pay extremely good attention to nationalized reports and take the precautions as I can.
I also bear in mind that we have moved from the house where we lived when we had dengue, and while it only takes one mosquito, the neighbors are far more fastidious, there are fewer absentee owners, and the Wolbachia program is in effect, which is good. The few mosquitos I have seen have not been Aedes but rather a smaller genus whose bite is far more painful, frankly.
A pik (the local name for the kissing bugs) was spotted at a park in this fraccionamiento a few evenings ago and promptly reported to the health division. They came and sprayed immediately (we have local social groups), but I know better than to scratch any itch, and I have seen the fogging trucks come past our house a few evenings as well. I review the symptoms of Chagas fairly often though, probably more than needed, if I am honest, just because I am aware it is something that if treated promptly can be OK but if not can shorten one’s life considerably.
Of course now having posted about all this, I feel itchy all over for no reason at all, hahaha.
Assassin Bugs… the thought of their rigid, beveld, straw-like mouth-part stabbing me has always kept me a fair distance from them. Reminds me of the plastic straws that came with Capri-Suns.
(The longest I had poison ivy was around 2 weeks and my legs were covered - behind the knees, ankles, between thighs. It was pretty bad but the blistering wasn’t as bad as I rememberd it from when I was a kid.)
Aedes albopictus, for very similar reasons. A. aegypti is fortunately not established around my area.
That’s my state of mind.
Mantis shrimp - even the little ones can give you a nasty cut; the big ones can slash you to ribbons in a nanosecond.
“I heard it can last a YEAR”
Luckily, if you are allergic to poison oak/ivy it cannot last a year. The rash/blisters can last 2 to three weeks. After you shower or wash the area thoroughly, no one can get urushiol (the oily sap which causes a contact dermatitis) on them from you. You can get more urushiol on you and other from your clothing until it is washed, so be careful when you pick it up and put it in the washer.
I guess prions don’t technically count as organisms, but they’re definitely the most terrifying to me. A random protein in your brain mis-folds, bumps into others and makes them mis-fold, and the process continues exponentially until your brain can’t function. There’s usually no particular reason for it to start, there’s no cure, and you deteriorate mentally for like a year and then die. At least with tigers and Komodo dragons and even poisonous plants/mushrooms, it seems like the danger is there for a reason- predators got to eat, prey got to defend itself from being eaten. But the randomness of a macromolecule just getting unpredictably bent in a weird way and now you’re 100% going to die next year but you just don’t know it yet really embodies the essence of existential dread in my mind. You can’t predict it, you can’t prevent it, you can’t fix it. It’s just a little agent of chaos slowly dragging its victim into the void for no purpose whatsoever.
I also got bit by a song sparrow once, and ouch! We should be more afraid of them I think. It’s only their good will that keeps us safe from those beaks. Lol
Gympie Gympie, RIP this observer https://www.inaturalist.org/observations/52514843
Guess it depends on what you mean by “scared”. If you’re talking about something that makes me acitvely do things and dread one getting on me unnoticed… blood-sucking ticks. TBE, Lyme borreliosis… And now they’ve confirmed horse flies can also spred Lyme’s. 
Otherwise, pathogenic bacteria. I’m not going crazy over them, but as things that’re as hard to avoid as they can’t be seen, and as potentially deadly, they cause maybe the most anxiety to me periodically.
I’m scared of:
Moose They are too large and their faces are so long.
Bears They are too large and the head is too wide.
Can vouch for that. Worked for Queensland Forestry quite a few years and sustained quite a few stings. This thing can get you through quite thick clothing, causes intense pain and makes your lymph nodes swell up. The pain eases after a day or so but will return if you get the affected areas wet or if the weather is cold. These symptoms can last for months. Dead leaves and dry stems can sting you as well and are harder to detect in the rainforest. Chopping a gympie gympie down fills the air with the fine stinging hairs which cause intense sneezing and release of mucus. The best treatment is to cover the affected area with a dry dressing and keep it warm.
I’m paranoid about invertebrates that parasitize humans, especially bedbugs.
As others have said, poison ivy definitely does not normally last a year. That would have to be a really extreme case. Most people just get an itchy rash that lasts a week or two. Some people aren’t even sensitive to it, although it is unwise to depend on that, because you can still develop the sensitivity. The main thing is not to burn it. You don’t want to breath aerosolized poison ivy. (But even then, it wouldn’t last a year.)
I’m afraid of the tick-borne illness that can make you allergic to meat, because I am an indifferent cook to start with (it’s not that I can’t, it’s that I don’t care), and I can’t afford to have such strict limitations on my diet.
And my totally irrational fear is of house centipedes. I can’t even look at them. They make my skin crawl. My skin is crawling just writing about them. I learned to love snakes, and I’m slowly working on spiders, but I cannot tolerate house centipedes enough to even start. I think it’s the way they move.
As for the organism that is most likely to hurt me, I seem to go through phases. One year it was nettles. This year it’s cacti–I have learned about glochids, the hard way.
horses. anything large makes me pretty nervous.
humans definitely!
lampreys and leeches just don’t sit right with me… all those teeth and the way they just grab on to you.. eueeuuee
a healthy fear/respect of certain predator animals like bears and mountain lions is warranted, simply due to the fact that they really do have the power to harm you.
on a darker note, I’m not too big on any genetically altered organism intended to hurt people (i.e. bioweapons). things like engineered viruses and biowarfare have much more relevant and practical reasons to be feared, compared to spiders and silly little bugs!
Probably ticks, especially Lone Star ticks. I’ve been bitten by many, never gotten a disease yet but I feel it’s only a matter of time.
I can’t stand poison ivy, but it’s more annoying than anything else. The rash doesn’t last a year, maybe a couple weeks at most
March flies! (Tabanidae) They make summer unbearable. They chase me. For some reason I am very attractive to the blood-sucking monsters!