Kerbarthropoda is the most diverse phylum on Kerbin, much like their Earth analogues. In fact, their names is a portmanteau of Kerbin and Arthropoda. While many of these animals are small and insignificant at first glance, the Kerbarthropods are very important components of Kerbin's ecosystems, helping decompose dead matter, serving their micro niches, and even providing a meal for larger animals.

There are over an estimated 1 million species in this phylum, around 450,000 of which are described, half of which are split between 2 major classes of insect like creatures, Lithoptera and Arthrodactyla. Both these clades are distinguished by whether their wings are protected by a hard casing or not. They are ubiquitous around Kerbin, able to be found in any habitat on Kerbin, except the poles, where it is too cold for anything else to survive. 

Other major Kerbarthropod groups include the Xenarachnids, which are basically Kerbin's equivalent of Chelicerates. These animals are characterised by their mobile pedipalps and claws, as well as their usually predatory nature.  Many species of this group are also able to produce venom and/or silk, depending on species. Another set few clades are of aquatic and/or microscopic inhabitance, resembling Rotifers, Chaetognaths  and Crustaceans. These inhabit various aquatic habitats on Kerbin, and there are thousands more species in at least 4 clades.

The Dragon Spider

The Dragon Spider is perhaps the most well documented Xenarachnid on Kerbin. Reaching lengths up to 15 cm in the largest specimens, these animals are highly prolific and scary predators. Like other members of its clade, it has 8 pairs of walking legs, each tipped with a single, serrated claw, for better grip. It is an ambush predator, constructing intricate traps made of it's silk, which is so strong, light and resilient, that it is economically vital for Kerbals. The Dragon Spider also has 2 large chelicerate-style pedipalps on its head tagma, tipped with scorpion-like claws, that it uses to restrain its prey, while its fang tipped mandibles bite into the hapless victim, injecting omnitoxic venom and digestive enzymes to destroy and liquify the victim from the inside. The predator can then slurp the delicious tissues out of the now dead prey organism like a meaty slushy. To see, the Dragon Spider has 12 eyes, the first 6 are its main eyes, positioned on the top of the head. These eyes are also positioned so as to predominantly look forward, giving the animal greater depth perception. These eyes are also made of hundreds of optical cells, which can be retracted into the external skull, so as to better protect them from the elements, as well as aiding in focus. The other 6 eyes are simpler, and located on eyestalks, which are the only soft parts of the animal's exoskeleton. These eyes are used to help the animal look behind, or to sense other non visual queues to an action.

The Dragon Spider inhabits many equatorial habitats of the Kerbinian surface, feeding on many different Kerbarthropods, including Bertles, Legcatchers, Butterbees, and other small prey, as well as small Gastrocerebrans, and even small Kerbinian vertebrates, like Bushmice. This varied diet is so, because the Dragon Spider, one of 3 species of its genus, resides anywhere warm on Kerbin, including large rainforests, where animal life, both on Kerbin and in general, tends to be most abundant.  The creature's dens are constructed using rocks. dirt and silk, which it intricately weaves into a webbed trap,  usually set up at a small distance away from the den, where it lies in wait for any unlucky organism to get stuck in the web. Once trapped, the prey animal is then envenomated, as the Dragon spider wraps silk around it. Once the prey animal is dead, the Dragon Spider will usually drag it to its burrow, which is usually located under rocks, to begin digestion. Many other Xenarachnids hunt like this, too.

As a Megarachnid, The Dragon Spider is sexually dimorphic: males are longer and slimmer, and females are bulkier and more rotund. Females also are the sex that hunts as described, with Males being more migratory, patrolling relatively large territories. A single male Dragon Spider territory may cover up to 10 female dens, with the male being able to breed with any female of his choosing. Unlike male tarantulas on Earth, male Dragon Spiders live about as long as females, and in fact, a male may outlive at least one of his females. During copulation, the male will manipulate the female's position so that she is on her back, after the male deposits a packet of sperm into her abdomen, usually through gonopodal contact. Once done, the male will leave to try to do the same to another female in his territory. After insemination, the female will lay up to 150 or so eggs, before taking care of the hatched spider lings, which will be able to fend for themselves up to 2 weeks after hatching.

The Whistler

The Whistler is one of the most unique Lithopterans on the face of Kerbin. It lives mostly in tropical rainforests, with habitats extending majorly north and south too. It is a herbivore, consuming plant matter, and it looks like a cross between a grasshopper and a beetle. The creature gets its name from its unique ability to make whistling calls, made from a complex passage system between its spiracles and mouth, giving it the ability to occasionally mouth-breathe, which is the trait it uses to produce these whistles, which may serve a variety of purposes, from confusing potential attackers to attracting potential mates. 

The Whistler's head is rather peculiar, as a result of its whistling talent. It is rather large, with thick antennae for enhanced audition and chemoreception. the mouth is also surrounded by many jointed mouth parts (only two shown on the drawing), which it uses to help feed on the tough foliage of the plants in its habitat, and to manipulate the whistling calls into intricate songs. As for the colour, the head possesses a strong shade of red, to help with display between individuals of the same species. the body is around 10 cm long, with a short thorax and a large abdomen, which the wing casing doesn't quite manage to extend over (not even close). The animal also has long, powerful hind legs, which it uses to hop long distances, like a grasshopper. 

The animal is often preyed upon by Megarachnids, like the Dragon Spider, as it is an easy meal. The Whistler doesn't seem to have many defences against predators, other than its jumping ability and powerful biting mandibles. However, some individuals have harnessed toxins in their exoskeletons, which sting when contacted by would-be attackers. This population is slowly diverging from its ancestors, and may or may not already be a separate species.

The Whistler is strictly herbivorous, despite its mouthparts, which it uses to masticate tough vegatation. It also feeds on many other parts of plants, such as seed, cracking them using those mouthparts.

The Whistler is monotypic, meaning that it is the only member of its genus. Other similar animals have existed millions of years ago, but as natural history progresses, many of the genus's species have died out, due to increasing competition. The rainforests to the west of the Loveheart Ocean, with their abundant food sources, serves as the refuge for the genus Sfyrigiostoma, and only the Whistler remains

The Kerbin Bee

The Kerbin Bee is, as you can  definitely tell from its name, Kerbin's analogue of bees. These animals are almost cosmopolitan, inhabiting almost every grassy area of the planet. They are eusocial insects, with a highly developed system of sociality and cooperative survival. They are members of large group of highly social Arthrodactyls, and as a result of their sociality, they are highly successful. The Kerbin bee is the epitome of Arthrodactyl sociality, evolving a eusocial life style, with a single queen prioritising all the breeding, and castes of workers and soldiers defending the hive from all intruders, including larger Xenoapids. The hives are complex in their construction, able to house thousands of individuals, and packed with lots of hexagonal cells, which can serve multiple purposes, from food storage, to nurseries. The Queen is, of course, the largest of a hive, and she is responsible for laying eggs. She can live for around 5 years, churning out eggs for her entire adult life, after establishing a colony. Interestingly, some workers can be sexually mature if the circumstances allow, as workers are usually sterile and often sexless. Those sexed workers will leave their original nest and become queens themselves, if female and discovered, to begin their own colonies, though at a reduced capability than a proper queen. Each summer, hives produce hundreds of male drones and princesses, which fly off into the wilderness to mate, the drones usually dying shortly after mating, and the princesses becoming queens and forming new colonies.

The Kerbin Bee is superficially wasp like, with a slender, yet also a bit of a stout body, which is covered with yellow and black stripes, an indication that it is venomous. It has long, jointed legs with curvable feet that can hook around thin enough branches when deciding to walk. Their mandibles are small for their head size and are used to help collect food to bring back to the colony. The animal has 2 large eyes, which serve as the main eyes able to sense many different spectra of light, and 2 smaller ocelli, which are able to only detect simple images.  The antennae are used for many different purposes, from communication, to sensing the environment through sound and olfaction.

Kerbin Bees are very important for Kerbals, as they and their kin are the number one pollinators of Kerbinian wildlife, helping spread the gametes of plants far and wide to other plants. This is very crucial for Kerbal agriculture, as many plants that the Kerbals have domesticated rely on pollination for reproduction. In addition to this service, Kerbin Bee hives also produce honey and bread, which is consumed by these creatures, whose workers measure around 2 cm on average. This honey is tasty, and highly valued by many Kerbal cultures, as is the bread. Both of these products were sought after commodities in Kerbal trade, and are exports of some minor Kerbal nations.

The Kricket

In one of the transition cards for Kerbal Space Program 2, there is a bug that is seen on the telescope, with one Kerbal astronomer looking at it in awe. This is the first canon lifeform on Kerbin, but we don't know how it works according to the devs, as it is irrelevant for the game. So the information presented is purely my headcanon.

The Kricket is a very common hopping Lithopteran. It has fairly large wings, and casings to protect said wings. Powerful jumping hind legs propel it through the grasses of the meadows and treelands that are commonplace around Kerbin's surface. The antennae are long, about as much so as the rest of the body.  It's eyes are the most peculiar. They are cartoonishly large, about as large as their head, which looks like a disadvantage at first glance, but they can be retracted when needed. These eyes are somewhat camera-like, a trait not found in any other Lithopterans, and can detect light with greater precision and accuracy. Their mouth also has multiple mouthparts used to shred vegetation, with grasses making up around 80% of their diet.

The Kricket is an easy meal for many small predators, such as Xenarachnids, Hawkmoths, Klizords, Bushmice, and others. They are also abundant animals, with their predators unable to make a dent in their populations. They even serve as snacks for some usually herbivorous animals, like Kerbin Bees, when they want to supplement their diet.

The Kricket resides in the temperate grasslands of Kerbin, the most common biome on the planet. This animal's range is split between all 3 continents and along with a few island. In fact, it is so populous and so widespread, that many Kerbal cultures have multiple names for the creatures, the most popular being 'Kricket', but 'Kerbug', and 'Krasshopper' are also common, although scientifically, these two latter names are to be used for other organisms. The Kricket is a mostly harmless animal, although it can be a pest, though thankfully not a major one.

The Kricket's adult life revolves around a living phase and a breeding phase, which are both relatively self-explanatory, and revolve every season. The breeding phase most often happens during Late Spring and Early Summer, where temperatures are high and the creature's food is most abundant. During this time, Kricket's congregate in large swarms, with the males calling out to receptive females. After a few weeks, of males breeding with females, the swarms dissipate, and the Krickets will go back to their usually solitary lives. Females will lay dozens of eggs, and the young are able to fend for themselves after hatching.