Asclepius' flies are similar in size to the ordinary housefly, but they are white, with crimson eyes (ugly little creatures). Unlike most flies, however, they are not diseased, in fact their remarkable immune system contains agents which tackle even human illnesses. This is the source of their white colouring also. The standard technique for capturing them, to use their juices, is to tempt one onto the palm of one's hand and then to quickly wring your palms, then rub the mush onto the afflicted area. This is not for the squeamish, but has definite healing possibilities.
Swordbiters are parasites. They are long, thin and silver, and digest metal, somewhat like rust monsters, but smaller and more insidious. They resemble stick insects, but when they cling to metal they are very well camouflaged, and one can be biting your sword for a week before you notice it. They cannot be removed by hand, as they are very strong, but if the blade is inserted into fire they will leap off to escape the flames. Sometimes, old treasure hoards are infested with them, and the first glimpse you get of the "glittering" weapons is a pile of rusted swords encrusted with these thin silvery insects.
An insignficant little species, the candlebug (or waxmoth) is a persistent bane for mages and merchants alike. Each the size of a small digit, these little scarabs thrive on wax and burrow up inside candles, ruining them. Sometimes a late-night worker will hear a crack and a sizzle as his candle expires, only to find the half-burned remains of a waxmoth squirming around on his desk. This is very annoying in worlds where candles are expensive...
Inspired by Ria Hawk's winged mushroom picture:
The winged mushrooms (Lerreta Meia) are a species of giant insect indigenous to the leafy areas of Udnalor, Kingdom of the Gnomes. Outwardly they appear much the same as ordinary giant mushrooms, and they graze in the bulbous fungal glades. However, this is merely an elaborate camouflage: the insect beneath is a fungivore and prone to fly off when it encounters another creature. Sometimes gnome farmers mistake them for crop mushrooms. They're in for a surprise when they do.
The ochre sands stretch for miles around. Something kicks up the dust. It's a yak. A desert-yak. It ambles slowly, nuzzling the ground for the low-growing shrubs. The ranger freezes. "Stay very still," he warns. "Don't move at all."
"What is it?" you ask, breathlessly.
"It's the most dangerous creature in the whole Ocadian desert. And it's about to eat that yak..."
The cliff-hunters ride sheer-stalkers vertically down the cliff faces to reach the nests of birds and steal their eggs for sport. Sheer-stalkers are vicious agile lizards about the size of large komodo dragons. They must be muzzled and harnessed, but even so there have been some nasty incidents...
Real World: some Indians in the Amazon treat their eyes with a traditional potion applied with palm leaves. Brutally painful, the drug alters vision, giving the jungle's dense green walls greater texture and dimension. You could adapt this to desert or swamps, or other hard to navigate regions.