Ants:

Marcher Ants, as they are referred to, inhabit the rainforests near Schendi.  The mass of black ants  moves through the jungles, usually forming a column that is about a yard wide, but that could be pasangs in length!  The column widens only when food is found.  It may then spread up to five hundred feet wide.

To cross small streams, the ants will make a bridge of themselves. During a rain, they will separate and seek shelter, reforming after the rains stop.  The bite of these ants is extremely painful but not poisonous.

Bees:

The books only depicted an instance of breeding bees for honey in Torvaldsland.  Although, the wide availability of honey throughout Gor seems to support bee keeping in many other regions.

Beetle:

One variety of beetle known to exist on Gor is the marsh beetle.

Flies:

There are many types of Gor including sand flies, arctic flies, and sting flies. Sand flies live in the Tahari and appear after the rains. The flies in the arctic are black and long-winged. Sting flies, also known as needle flies in the southern regions, usually live in deltas and similar wet areas. They generally lay their eggs on the stems of rence plants. They tend to be attracted to eyes and cause a painful sting. Several stings can cause nausea and a swelling that will go away after a few Ahn. But, in great numbers they can kill. The hatching time is the most dangerous period and last for four to five days. Luckily, that season is predictable so can be easily avoided.

"Following such rains, great clouds of sand flies appear, wakened from dormancy. These feast on kaiila and men. Normally, flying insects are found only in the vicinity of the oases."

~Tribesmen of Gor, page 152~

Gitches:

These are insects that cause a painful bite. Some can grow quite large.

Golden Beetle:

One of the most unique and dangerous creatures in the Nest is the Golden Beetle, that lives in the unlit caverns beneath the Sardar caves of the Priest-Kings. This is an insect the size of a rhinoceros. Its back seems divided into two thick casings which once long ago might have been horny wings but which have fused into a thick, immobile golden shell. It has glowing eyes and its head can almost withdraw beneath the shell. It can still use its jaws when its head is beneath the shell. It has two multiply-hooked, hollow, pincerlike extensions that meet at the tips about a yard beyond its body. These suck a creature's fluids out. Its antennae are very short, curved and topped with a fluff of golden hair. There are also several long, golden strands that extend from its head over its domed back and fall almost to the floor behind it. Its bite has a paralytic venom. It hisses and can move fast but only for a brief time. Its greatest weapon is that it exudes an odor, somewhat oppressive, that induces sleep in people nearby. This is even effective on Priest-Kings. Its primary food is Priest-Kings. It lays its eggs, each about the size of a fist, in a host. The egg has leathery shell and the baby is the size of a child's turtle. The host will not die if the eggs are removed before they hatch.

"It was about the size of a rhinoceros and the first thing I noticed after the glowing eyes were two multiply hooked, tubular, hollow, pincerlike extension that met at the tips perhaps a yard beyond its body.They seemed clearly some aberrant mutation of its jaws. Its antennae, unlike those of the Priest-Kings, were very short. They curved and were tipped with a fluff of golden hair. Most strangely perhaps were several long, golden strands, almost a mane, which extended from the creatures head over its domed golden back and fell almost to the floor behind it. The back itself seemed divided into two thick casings which might once, ages before, have been horny wings, but now the tissues had, at the points of touching together, fused in such a way as to form what was for all practical purposes a thick, immobile golden shell."

~Priest-Kings of Gor, page 180~

Grasshopper:

In the rainforests, there is a red grasshopper that weighs about four ounces.

Hinti:

These are small, flea like insects though they are not parasites.

Lice:

Lice vary in size from very tiny to the size of marbles. The larger variety infest tarns so tarnsman must remove them. When they remove them, they might feed them to the tarn. Lice can be dangerous though as they transmit the pox.

Rennels:

These are crablike desert insects with a poisonous bite though it is not too lethal. They leave little red bites.

"...that once an army of a thousand wagons turned aside because a swarm of rennels, poisonous, crablike desert insects, did not defend its broken nest..."

~Nomads of Gor, page 27~

Roach:

This is commonly an oblong, flat-bodied black creature about half a hort long. It has long feelers and is basically harmless.

Slime Worm:

This is a long, whitish, wormlike animal that resides in the Sardar. It is eyeless and has a small, red mouth on the underside of its body. It inches its way along, hugging the angle between the wall and floor. It once functioned as a sewerage device but it has not done so for thousands of years. It now scavenges on the kills of the Golden Beetle.

"We had not walked far when we passed a long, wormlike animal, eyeless, with a small red mouth, that inched its way along the corridor, hugging the angle between the wall and the floor....
'What do you call it?' I asked.
'Oh,' said one of the slaves, 'it is a Slime Worm.'...
'It scavenges on the kills of the Golden Beetle...' "

~Priest-Kings of Gor, pages 105-106~

Spiders:

One unique type of spider on Gor is the rock spider. They are usually brown or black and when they fold their legs beneath them, they look almost like a rock. Rock spiders can be huge, almost eight feet thick. They live in the rainforests. Cell spiders are tiny creatures.

Swamp Spiders, actually these are known as the Spider People, they are rational and speak to humans through the use of a translator device.  They are large spiders that live in the swamps near Ar.

"Approaching me, stepping daintily for all its bulk, prancing over the strands, came one of the Swamp Spiders of Gor....and I caught sight of the mandibles, like curved knives...He then backed away from me on his eight legs...I saw then for the first time that strapped to his abdomen, was a translation device....They hunt us and leave only enough of us alive to spin the Cur-lon Fiber used in the mills of Ar."

~Tarnsman of Gor, pages 81-83~

Termites:

They are also called white ants.

Toos:

This is a crablike creature, covered with overlapping plating, that resides in the Sardar. It lives on discarded fungus spores.

Vints:

These are tiny, sand-colored insects.

Zarlit fly:

This is a large, harmless, purple insect about two feet long with four translucent wings spanning a yard across. It is insectivorous. It hums over water and alights on the water with its padlike feet daintily walking across the surface.

"I did see a large, harmless zarlit fly, purple, about two feet long with four translucent wings, spanning about a yard, humming over the surface of the water, then alighting and, on its padlike feet, daintily picking its way across the surface."

~Raiders of Gor, page 5~

Unnamed creatures:

There are a few creatures that exist in the Sardar that were described but never named.

There is a segmented arthropod, about eight feet long and three feet high, with multiple legs. It has eye stalks, pincers, and its body plates rustle like plastic armor. It is a timid creature that does not like the sight of men.