On land, decapods, arthropods, gastropods, and their ilk occupy the lower links in the food chain. This is as true in the monster kingdom as it is in the animal kingdom. While many monster species remain undiscovered, these are the most common creepy crawlies found on Monster Island.

Demeking
Length: 58 meters
Height: 30 meters
Mass: 45,000 metric tons
Demeking occasionally venture to the surface to explore or seek out superheated materials to consume, but their slow speed and weak defenses leave them vulnerable to predators. In addition to their physical frailty, demeking are also not very intelligent. Demeking do have one ability that elevates them above just another meal - they can project a stream of fire from the orifice on their heads. This orifice is not their mouth - the mouth is located on the bottom of their foot, consuming edible material as demeking slides over it. Though demeking lacks the swiftness or dexterity to use this weapon effectively, deploying it is often sufficient to ward off would-be predators. Their lack of aggression renders them little more than a curiosity, but something in their DNA puzzles G-Force researchers. When exposed to extreme temperatures demeking cells undergo rapid division and mutation. Though they are drawn to heat, demeking avoid direct contact with fire and other extremely hot things. It has yet to be seen what would happen to a demeking specimen if its entire body was exposed to intense heat...

Gimantis Nymphs
Height: 1.57 meters
Weight: 362 kilograms

Gimantis Adults
Length: 40 meters
Height: 16 meters
Weight: 30,000 metric tons
These two are commonly found food sources on Monster Island. More information can be found here.

Spiga
Length: 116 meters
Mass: 60,000 metric tons
Spiga occupy roles lower and higher in the food chain. Alone, they can be easy pickings for the larger predatory monsters. In packs, spiga can turn the tables on those very same predators. More information can be found here.

Megalon Larvae
Length: 50 meters
Mass: 46,000
Megalon larvae are very common. They consume decaying megafloral plant matter and radioactive minerals, and their excretions leave traces of radiation in the soil they leave behind, which in turn allows for megafloral species to thrive. Megalon larvae are also an extremely popular food source among monsters. Megalon larvae are neonates, meaning that they live their lives without metamorphosing into an adult form. The adult beetle Megalon is the only exception ever observed on the surface. More information about Megalon can be found here.

Meganulon
Length: 3 meters
Height: 1.12 meters
Mass: 345 kilograms

Meganeura
Length: 60 meters
Mass: 40,000 metric tons
Meganulon live the first stage of their lives in the water, hunting fish and other aquatic creatures and ambushing smaller monsters along the shores of lakes and rivers. As they grow older, meganulon transition to a terrestrial lifestyle where they continue on as ambush predators, lying in wait for prey from the branches of trees. Once they have attained a certain size, they molt into the adult meganeura.

In the monster kingdom, meganeura occupy the same niche as mosquitoes. Using their stingers, they drain radioactive blood from monsters. Meganeura mate several times per year, laying clutches of eggs in the megafloral reeds that grow along the shores of Monster Island's bodies of water where the lifecycle begins again.

MUTO Nymphs
Length: 3 meters
Mass: 275 kilograms
MUTO nymphs are detritivores, eating decaying plant and animal matter for sustenance. They are slow, weak, and fragile, but numerous. Most monsters avoid preying on them due to their status as the de-facto dung beetle of the monster kingdom. Though they have a reputation for being disgusting filthy monsters, they are universally feared by all monsters with the wherewithal to understand the danger they present. More on the MUTO nymph to come.

Shockirus Mites
Height: 2.65 meters
Mass: 435 kilograms
Shockirus mites are like ticks for monsters. They can be picked off easily enough, either by the host or by a friendly monster. They live at the bottom of the ocean, eating scraps and waiting for an unsuspecting host to come along. Monsters can go weeks without noticing that a mite has latched on, and the mites only cause mild irritation to the monster at worst. It is a completely different story for humans.

In order for them to navigate the ocean floor, shockirus mites have developed extremely powerful appendages. On land, they can leap tall buildings in a single bound and run at speeds of up to seventy five miles per hour. When dislodged from a monster, they will hunt down anything that moves - even if the prey item is not sufficiently irradiated to provide nourishment. A human unlucky enough to survive a bite from a mite will die within an hour of being bitten; the noxious chemicals in the shockirus's bite create a rapid and deadly buildup in gasses in the human body until the body explodes.

Skjцrps
Length: 37.5 meters
Mass: 27,500 metric tons
Ts-eh-go is not the only monster scorpion in town, but his distant cousins have little in common with him. While Ts-eh-go uses his bulky tail and claws as sledgehammers and wrecking balls, the smaller skjцrps use speed and venom to take down their prey. Their chitinous armor offers some protection from predators like Rodan and Gorosaurus, who prefer food that is less prone to sting them. They are a favorite snack of Varan, who is immune to venom. Monsters that can breathe fire can also neutralize the venom by burning it. A single skjцrp is also capable of taking on a pack of up to three spiga, and is one of the few monsters on the island that actively hunts the giant spiders.

Triops
Length: 25 meters
Mass: 23,000 metric tons
These wholly aquatic, simple herbivores are found in the rivers and lakes of Monster Island. Triops are found in all environments and reproduce quickly, making them one of the staples of all monster kingdom food chains. Their sheer numbers make up for their lack of meaningful defenses and absence of offensive powers.

Tractor Bugs
Height: 15 meters
Length: 50 meters
Mass: 55,000 metric tons
Like triops, tractor bugs are simple vegetarians. They earned their nickname for the way they leave straight trails along the grasslands of Monster Island as the adults mindlessly consume vegetation. Juveniles are commonly found in the forests of Monster Island, climbing trees to eat leaves and fruits growing in the forest canopy. As they grow larger their weight prevents them from easily accessing these food sources, and so adults move into wider open spaces. When threatened, tractor bugs will curl into a ball. Their chitin is slippery and durable; though not impervious by any stretch, many predators opt to seek prey elsewhere. For the patient carnivore, one only needs to wait a few hours before the tractor bug's muscles weaken before it can be pulled apart.

Shinomura
Size: Variable
Mass: Variable
Individual shinomura vary in size from about the size of a housecat to the size of a deer. Individual specimens are relatively harmless, but in larger groups they become wildly aggressive. Shinomura swarms tear through the land like locusts, paralyzing monsters with their neurotoxin and draining their radioactive blood. More on shinomura to come.

https://www.deviantart.com/grumbletron/art/All-Monsters-Attack-Monster-Island-Bestiary-1-865900378