Do you honestly believe that?
A creature claw than can match a 30mm sabot round?
A carpace that is more resistant than our armor?
Here you are, Armored Space Marine Bob. You have an armored power exoskeleton stealth suite, a railgun, a jump pack, a flamethrower, a lot of grenades, and links to some drones overhead. You're pretty well-equipped.
You have been deployed to Planet Y, which is known for relatively hostile lifeforms. You have been separated from your team due to enemy activity. Hooking into your satellite navigation system, you find a nearby predesignated rally point.
As you're heading that way, you pick up thermal and motion coming your way. It's some kind of life-form, a bit bigger than a tiger. There's no catalog for this planet yet, but you're not an idiot. You target the thing (through trees, foliage, and anything else in the way) and shoot it with your railgun.
The railgun projectile blips right through it without transferring any kinetic energy. That's okay, though, because your servo-assisted shot hits it right in the brain. It dies.
The moral of the story? 99% of the time any space marine will be able to handle the local fauna.
Now, here's the 1%.
Now you're on some freaky-ass low-gravity hell planet. Same scenario. There are no trees, but the clouds above are strange, ominous, dark. Vast, organic shapes move amongst them. The air is full of a strange haze. Upon closer examination, you realize it's not haze: it's a soup of tiny organisms, insects of some kind. Slow-moving but purposeful. They're caking on your suit, secreting some kind of nasty acid. Fortunately your suit isn't particularly reactive, so it shrugs it off.
The issue is your jump pack nozzles. They're thick in there, almost clogging them. Firing the pack would probably clear the blockage, but the chances of a backfire (gutting your suit) are pretty good. You check your railgun's protective housing, just to be sure - the naked rails are more vulnerable than your armor.
Lightning rumbles above you, leaping from cloud to cloud. About this time your drones overhead start dropping out of contact. You transit a climb order to the drones, ordering them to get above the cloud deck, wondering why their threat detection algorithms didn't already put them at a safe altitude.
Your sensors are futzing up, but you can see that some kind of enormous mass is settling towards you from the clouds above. Looking up, you see nothing. Only after some examination do you realize that there is an
organism above you, something like an aerial jellyfish: extraordinarily diffuse, mostly water. There are nodes and organs scattered about it, visible as sacs and spines within its bulk.
Tentacles brush against your suit, probing, exploring. You check your hardseal - secure. Electricity crackles along the curves and recesses of the organism above you, this kilometer-wide colony creature. It sparkles with eerie phosphorescence.
Like a good space marine, you light it up. Flamethrower, then hive rounds from the railgun. It burns. Parts of it detonate in petroleum-fueled secondary detonations. Its flaming ruins settle over you and you stomp out of the burning mess and on towards the rally point.
Another one of the vast jellyfish creatures moves overhead. Bigger. Stranger. It unspools kilometer-long tentacles and probes at you. You open fire again, but the flamethrower washes over it harmlessly. On a world where the atmosphere itself could ignite, many of the big organisms are thermal-adapted. Your hive rounds shred organs within its bulk, but you see no real effect. Lightning crackles over its lobes, descends its tentacles.
You turn your attention to the probing limbs. Your left arm houses a monomolecular blade that will open tank armor. You sweep in broad arcs, cutting the tentacles away.
Abruptly, impossibly, you are jerked airborne. Thunder ripples over you. There is nothing holding you up. You check your EM sensors and find that you're being levitated by electromagnetic point manipulation - the trick they use to levitate mice in school. The creature has extraordinary capabilities. It must gather current differentials from the thunderclouds above. It can control electricity.
You take a risk and fire your jump packs. Propellant ignites, but the cake of organisms in the vent is too thick. Backblast blows safety hatches open and shreds the nozzles. The blast tumbles you, and for a moment you're free, but the leviathan above reclaims its lock on you.
More tentacles drape across you. You go for the big guns and fire anti-aircraft weapons into the soup above (wishing you had nukes.) They send compression waves through the cloud monster, and the patterns of lightning above begin to grow ragged. But your sensors tell you that another creature is edging in from the south.
The clouds are alive and they speak to each other. Perhaps they are all cells of one creature.
You cut away at the encroaching tentacles as rapidly as you can. They fall away in great, curtained sweeps. The sky above lights up blue as the creature does something, and the tentacles gathering around you (faster than you can cut - insubstantial, feathered, somehow congealing again behind your blade) come alive with current. Millions of volts. A thunderstorm's worth.
The yield of the average thunderstorm is nine kilotons. The creature channels that power into you. Your suit is nonconductive and protected against electrical attacks. You're fine. But the rails of your railgun, protruding from their housing, bend apart and detonate into a spray of projectiles. They patter off your suit and fall below. The flamethrower attachment detonates, tumbling you.
The shrapnel stops, hovers for a moment, and comes back your way. The creature throws them with its EM sense. They achieve respectable velocities but can't breach your armor.
Standoff. You're wreathed in current, but insulated. You can keep hacking at the tentacles with your monomolecular blade, but it's like trying to chop a jellyfish in half: they're not really substantial enough to cut.
Then the predators come. Symbiotes that live within the cloud creatures. Nine swift manta-shaped creatures, moving along the field lines in long, swift spirals. They hit you with their particular adaption: flammable jelly sprayed from an orifice on their undersides. The crackling current ignites it into something like napalm.
Your suit is good, but it can't defy thermodynamics. Inevitably, you cook to death.
When the military finds out what happens to you they abandon the planet and nuke the biosphere to the bedrock. Nothing ever lives there again. Technology wins! But, nonetheless, one space marine type ran into more than he could handle, and this just goes to show that although nature may be outclassed, it'll probably produce a few surprises.
