In my novel, Cleaning Up The Future, many of the insects and animals have become larger in the country of New Cinalia after several awful nuclear attacks. So far praying mantis and squirrels have attacked the main character but they were easily dispatched by guns.
What insects or small animals do you think would be hardest to kill if they were larger?
What bugs are you afraid of?
Cockroaches, ants, termites, worms, spiders think of whats in every day back gardens etc. Those will be the real hassle because of the quantity.
Cockroach.... Even if you cut their head, they still can move by instinct before dies 2 weeks later because of starvation. Make a horde of roaches lead by a King Cockroach. Those are my favorite insects in my time as Tabletop game Gamemaster.
Talking about scary, how about Japanese Giant Hornet and Saddleback Caterpillar? They're deadly to humans even now. If they're mutated & become stronger.... Well, I think it's not strange if there is a human country which is fallen down and colonized by a nest of Giant Hornets led by their Queen.
Leeches. They are scary! Their bodies are cold and damp and elastic, and they suck out your blood and stick to your skin so hard you scream in fear while trying to pull them off! My worst nightmare would be to be bitten by lots of leeches until they are bloated with blood, and still they want more 
. I might pass out just thinking about it 
.
Where I live we get leeches in our backyard during rainy season. During this time I won't ever go out into the yard 
.
Some type of beetle with hard shells
Catepie can evolve into metapods, but their attacks are not scary.
LetThereBeMagic I’ve actually had a leech on my thigh before. I was swimming in a river and crawled out along the muddy side. When I was standing to dry off with my towel, I looked down and lo’ and behold a leech size of my little kid hand on my thigh. I screamed, slapped at myself, and tried to scratch my own skin off. It got off. I never swam in that river again.
Vanadhi_Lucia I have heard of the Japanese hornet, but I have not researched it much.
Look at this quote from wikipedia: "An individual hornet can kill forty European honey bees a minute while a group of 30 hornets can destroy an entire hive containing 30,000 bees in less than four hours.[3] The hornets kill and dismember the bees, returning to their nest with the bee thoraxes, which they feed to their larvae, leaving heads and limbs behind. The honey and bee larvae are also taken to feed the hornet larvae."
WOW, they are vicious. Also, they are very practical. They use almost all of their preys stuff to feed their own. WOW.
ALSO, I didn't know caterpillars could sting. The venom from the Saddleback Caterpillar can induce "severe symptoms ..... migraines, gastrointestinal symptoms, asthma complications, anaphylactic shock, rupturing of erythrocytes, and hemorrhaging."
Very interesting.
Thank you for making me aware of those two creatures.
I don't know if this comes under bugs but the first thing that comes to my mind about scary insects is lizard.
I hate them! Yuck Yuck Nasty! Seeing one is enough to give me goosebumps all over my skin. I guess this fear of lizards is because of my childhood experience when a lizard fell over my head. Devastating! Truly!
Parasites that dig into your skin are the most frightening. Imagine a worm longer than your body spread throughout your innards. They can get in through your ear, mouth, nose or any hole and lay eggs. If you’re writing a novel it would be a terrifying scene to picture a gigantic worm chewing its way out of a body after it’s done growing and leaving larvae that attack the party in their sleep after the mother escapes.
23DN4L 
... props to you for being clear-headed enough not to panic. I would have screamed and jumped around like a headless chicken while trying to pull it off.... Now I'm getting goosebumps
UnderTaker26
I dont wanna imagine. You re giving me goosebumps.
23DN4L a tick could dry up humans if they are larger, same with mosquitoes. Fleas have this energy storage thing that could multiply their speed. That's why they could easily jump 100x their height, or flip a coin if you put it over them.
23DN4L there are also obvious ones like black widows, tarantulas and bullet ants. Black widows and bullet ants could already kill humans from their original size.
How about attacked by mob?
Mob of insect is more scary than one insect with OP defense
Any of these would be a nightmare
http://quietfanatics.blogspot.com/2013/03/5-horrifying-texas-insects.html
bachingchung
You’ve listed a lot of good creepers.
Fun Fac: The black widows favorite form of birth control is eating their mate after first pregnancy. #tilldeathdoyoupart
Bullets ants are the cowboys of the wild world shooting people up with their sting. They don’t even need a gun and hands. Them and fire ants are the reason I’m afraid of all ants.
UnderTaker26
Indeed! That would be horrific! I almost want to wear earmuffs while sleeping now.
23DN4L centipede! with its many legs, no matter how fast you run, it still can catch you Muahahaha
I can recommend a manga with similar type with your story: Kyochuu Rettou
That manga also tells about a bunch survivor from the wrecked ship that landed on a mysterious island that filled with giant insect
Lord_HaarT centipede reminds me if Kaneki. Ugh nonono I don't want to remember his days of torture
Jinu_June there's only one place where comodo dragon can be seen in their natural habitat, or else you can only see them in certain zoo, like zoo in Rotterdam, Sydney and Singapore 
SweetsTomato Well I know you can see komodo dragons in zoo. But where is their natual habitat?
Jinu_June Indonesia. Nusa tenggara island, and some small island around there. Only can be reach by boat 
Jinu_June yes, it can be seen as giant lizard. Somehow different with thread starter ask, which is insect
LetThereBeMagic leeches isn't that scary, in fact they even used in medical world.
Traditionally, leech can be used to suck dirty blood from ulcers or abscess.
The more legs the creepier. Spiders, centipedes, millipedes. Aside from that, worms are creepy. Anything that wriggles. If you want it to be creep you can make it burrow into people? Like a centipede that crawls into people's veins or something.
23DN4L Let's just be thankful that must bugs and instincts don't travels in packs. Imagine a pack of black widows
or scorpions
Also, if snails are so slow how come nobody sees them coming? Is just like bamm!! there's a snail 
Creepy little turds.
The bug that could shut down WN's server.
Citlalicue Actually this isn't quite correct. Many flying insects swarm, ants of course live together under a queen/queens in colonies, some spiders and scorpions mothers will carry their young with them on their back. Bee's & wasps have hives.
For example,
Or
checkm8 Well, yeah but most don't, once they're grown (scorpions & spiders) are on their own. I kill at least one or two scorpions per week inside my house. I don't know what I would do if I see 20 or 30 coming at me, or crawling on my legs like sometimes ants do Also bees, wasps and ants don't tent to make nest inside houses like, spiders, scorpions and cockroaches do.
Those pics are gross by the way
think of those insects that has insane ability for example ants can carry things, I don't how many times of their body weight... Imagine when their sizes are that of a human. I know ants don't look scary now but when they grow so big and make a colony... I'll be the one who's running first.
