The arboreal isopods (order Scansoriarthriformes) are some of the earliest-branching pill bugs on Apterra. Their ancestors first split off from a common ancestor with the Plague, their closest cousins, as far back as the Dawn Muricene, becoming a distinct species sometime around 50,000 PA. They quickly came to dominate their niche, outcompeting any other crustaceans that attempted to establish a mutualistic relationship with woodlouse-grasses. As their hosts began to diversify, so did these early Scansoriarthriforms, with the ancestors of groups like the sheriffs emerging soon after the palm-grasses speciated. More derived genera cropped up around the turn of the Middle Muricene, with specialists like the flipbugs, snatchers, staghorns, and rangers flourishing as nectar-producing plants became commonplace. Others abandoned the pseudoforests, devoting themselves to skystalk hosts as the latter group expanded across all terrestrial habitats. Though their bodies and lifestyles have changed drastically, all members of this order were united in their fierce struggle against their own sister clade.
Sheriff woodlice (Altiperiidae), one of the most basal Scansoriarthriforms, play a numbers game to protect their homes. They spend most of their time acting as generalistic scavengers, feeding opportunistically on mold, nectar, and rotting foliage. When the Plague attacks, though, they have an extremely specific and effective strategy to repel the invasion. By wedging their sharp exoskeletons into tree trunks, they form nearly impenetrable walls with their own bodies, blocking the advances of the Plague. The family has existed for many millions of years, predating both the hybrid trees and their mycad ancestors. In the days before true trees existed, their defensive strategies often inflicted damage on the palm-grasses they relied on. They were simply the lesser evil from the pseudotrees' perspective; though they regularly caused scarring and put the plant in danger of infection, they protected it from complete defoliation.
Today, with the newfound dominance of palm-grasses descended from Ice Age hybrid trees, this trade-off is no longer a concern. Dendrifex mushrooms (family Poamycaceae), descended from Poamyces dendrifex, can recognize physical damage caused by the sheriffs' spines. In response, the fungus secretes a massive dose of Dendrase enzymes, promoting rapid healing at the site of the injury. Sheriffs can now be much more aggressive, jamming themselves deep into the trees' tough, fleshy culms to ensure no Pestilarthrids can make it through the barrier. Taking this ability to its logical extreme is the Broncobug (Cuneotelson), a genus that makes its home in only the largest trees. They have reduced the thorny extensions of their body segments, relying solely on a long, sharp pair of tails to keep them anchored. This pleotelson can reach nearly two centimeters long and is almost impossible to dislodge by force. When the Plague arrives, broncobugs can rear up, remaining fixed in place while they bite and tear into the bodies of their assailants. This is also an effective anti-bridgeworm strategy, as it allows these flexible Altiperiids to nip at the dodecipedes' soft underbellies.
Leechbugs (Sacchararthridae) were another early-diverging arboreal group. They evolved at a time when their order's partnership with woodlouse-grasses was still in its infancy and as such never developed strong instincts to protect their hosts. Instead, they became well-hidden parasites, feeding on sap and disguising their scent to go unnoticed by their relatives. As time went on, however, they became more and more genetically distant from other Scansoriarthrids, and it became harder to blend in. Lacking the Plague's massive offensive forces or sugarflies' nimble flight, they gradually found themselves at a distinct disadvantage in the competition against other woodlouse-grass-eaters. The Great Decarbonisation further reduced their numbers, as there was little to feed on for many decades before forests began to regrow. In the modern day, only one genus of Sacchararthrid remains. Endemic to grasslands of Panapterra, the Nectarleech (Floricisor) takes advantage of less well-defended sweetstalks to sustain itself. Without large and dedicated colonies of defenders, the Culicosaccharaceae are comparatively easy targets. However, they secrete nectar only within their flowers, and nectarleeches do not have a long proboscis to reach inside. Instead, they use their scalpel-like mandibles to slice open the bottom of sweetstalk florets, drinking the sweet sap that drips from the wound. This has sparked an arms race, with the flowers evolving stronger protective bracts and glumes to safeguard their innards, while the leechbugs increase the strength and precision of their cutting implements.
One of the oddest-looking taxa within the arboreal group is the Platyarthridae, also known as flipbugs. They initially evolved to hide in the rough rings of leaf scars ubiquitous to palm-grasses, lying in wait until they saw an opportunity to violently eject a Plague woodlouse. When bridgeworms entered the scene, this became a less viable strategy, as the long-bodied squashroaches could easily span the dangerous areas, allowing their smaller comrades to pass safely. In response, bladetrap bugs emerged. Their flat, green bodies blended in with the smooth internodes of tree mycads, and their large size allowed them to send even the biggest dodecipedes flying, and though their camouflage was at first rudimentary, over many generations they became more far difficult to detect.
The most specialized Platyarthrid is the Barkflap (Squamularthrus), a bladetrap bug that appears nearly invisible against the backdrop of a hybrid tree. They are slow-moving, slow-growing, and require little food to survive. What little they need can be acquired without taking a single step, as they exclusively feed on droplets of their host's nectar. Remaining stationary, this genus is rarely spotted by adversaries until it's too late. Facing upward and biting into the palm-grass with its mandibles and jumping with its strong legs, the woodlouse hinges off the plant and catapults its foe into the distance. They provide an invaluable service to the tree, and this benefit is proportional to how many individuals are present; greater numbers can protect a larger percentage of their host's surface area. In some regions, there are so many barkflaps that they nearly cover the entire palm-grass, forming a living bark across its entire stalk. Young mancae generally cling to smaller branches, while their full-grown parents are more commonly found on the main trunk. In these densities, Squamularthrus display their other unique ability: when packed close together, they can easily trigger each other's defensive behavior. This too is a tool in their fight against the Plague; they often allow the approaching army to advance far up the stem before one barkflap reaches its limit and reacts. In a matter of seconds, the rest of the fast-opening, scale-shaped isopods respond in kind, sending a mesmerizing wave rippling away from its source. This chain reaction quickly rids the woodlouse-grass of Pestilarthrids and dodecipedes alike. If successful, hundreds can be evicted from the battleground in the blink of an eye. On the other hand, if this maneuver is poorly timed, it can allow the Plague to slip underneath the barkflaps, in which case the fight is almost certainly lost.
The remaining species all belong to a single, derived clade characterized by high metabolisms, fast movement, and an upright posture supported by their first few pairs of legs. Among these, the first to rise to prominence was the snatcher, a clawed predator known for tearing its enemies in half with its powerful forelimbs. Its descendants are called the Brachiarthrids. These large isopods are feared ambush hunters, hiding in dense foliage and waiting for prey to wander by. The largest is a swamp-dweller from Choeropica called Prementarsus. The dactyl segment of its front legs has many backward-pointing spines, letting it grip its prey. Once caught, the victim has nearly no chance of escape. However, these giant snatchers are not so formidable in the open, as their armor is relatively weak and they are in grave danger of being carried off by eagleflies and other bugs of prey.
By far the largest family in this order is the Cursoriarthridae. This group of running bugs includes the closely-related descendants of rangers and staghorn woodlice. An example of the former is the Forest Ranger (Pestilasseclus), a small and sneaky nectarivore that shadows Plague colonies as they march through hybrid forests across Panapterra. Quick on their feet, they watch carefully until the grazers begin preparing for an attack. Rushing ahead of the crowd, they deliver an early warning to other local Scansoriarthriforms and receive free access to palm-grass sap as a reward. Similar to their ancestors, forest rangers are solitary, with the only amiable interactions with conspecifics occurring when males and females mate. The rest of the time, pill bugs of this genus simply patrol their territory, never straying outside the boundaries established by repeated scuffles with their neighbors. Unlike their nomadic predecessors, they may go months without an encounter with the Plague. A disadvantage of this lifestyle is that forest rangers must fast for long periods; if they repeatedly approach arboreal colonies for food when there is no danger, the residents are likely to drive them away or kill them. Conversely, when sounding the alarm, the amount of nectar they'll be allowed to eat is based on how far in advance they arrive. As a result, forest rangers have evolved into the fastest isopods (proportional to body size) on all of Apterra. Standing tall on their front three leg pairs, the centimeter-long arthropods can easily move twenty body lengths per second at a brisk jog, and nearly half a meter per second in a sprint, though this can only be sustained for a brief moment.
The staghorn branch of the Cursoriarthrid family also has small, fleet-footed members, one of which is the Sweetstag (Saccharocornis). Their lifestyle is somewhat convergent with the forest rangers; they too hold long-term territories containing many plants. As their name implies, though, this genus prefers skystalks to palm-grasses, specifically the abundant sweetstalks. Another difference is that adult sweetstags do not usually feed on nectar. As sweetstalks only produce this sugary liquid when blooming, these miniature staghorns must turn to other food sources. They are primarily carnivorous, though they won't pass up the chance to snack on fungi that threaten to infect the woodlouse-grasses. They rely on the skystalks mostly as a safe place to raise their young, whose mouthparts are not strong enough to kill prey until their third molt. Since sweetstags are not pollinators like dustflies, they can be considered parasites of the grasses, which gain nothing from feeding them. As with their other enemies the nectarleeches, the flowers are forced to devise methods of keeping the moochers out. In this case, many species have evolved to have narrow openings, allowing the dustfly's thin proboscis to access the nectar but preventing the staghorns from entering. In turn, Saccharocornis have begun to give birth at earlier and earlier stages, ensuring their newborns will be small enough to squeeze into the tight gap. By timing the birth of their mancae with the plants' flowering, they also provide their offspring steady supply of nectar for the first couple weeks of their life. By the time the sweetstalk dies, the fast-growing woodlice will be able to fend for themselves, dispersing to establish territories of their own. As adults, they are generalistic hunters of other isopods. They have a particular taste for Plague woodlice, which they instinctively kill on sight even when not hungry. This was originally a holdover from their ancestors' days as ferocious palm-grass defenders, but now serves a new purpose. By reducing the size of Plague swarms, they make the grassland safer for their dispersing young. The many Pestilarthrid corpses then fertilize the ground, guaranteeing that the next year's mancae will find many suitable homes. In this way, the sweetstags repay what they took from the skystalks, which end up receiving more nutrients than they lost.
Though life on the temperate grassland can be harsh, the semiarid savanna poses unique dangers that make survival impssible for small, poorly-defended genera like the sweetstag. Larger staghorns have risen to the challenge, braving Pugilopsids, pillbirds, and insectivorous mammals. Without the protection of tall grasses like the jade skystalk, the bare ground leaves these Cursoriarthrids especially vulnerable. The Stagmouse (Fortipedarthrus) can withstand all these threats, using its sharp eyesight and impressive running skills to keep itself safe. Though its compound eyes don't form a detailed image, they are finely tuned to detect any unexpected movement, after which the stagmouse scampers off to find a dark crevice to hide in. As large as a small rodent and just as speedy, stagmice abandoned the trees in the aftermath of the Ice Age, filling the niches formerly dominated by small, generalistic rats, many of which had gone extinct due to hypoxia thousands of years prior. They now have no relationship with woodlouse-grasses, but they often form alliances with castlebugs, as both face similar predators. For example, when an eaglefly approaches, the stagmice will alert the Thyrearthrids, giving them enough time to group up and form a defensive circle, distracting the predator while the stagmice flee to safety. This grants both isopods a better chance of survival than they would face on their own.