Gummygrubs

Gummygrubs (Caudocruinae) are a subfamily of large neotenic mosquitoes in the airgill clade, Spiraculobranchidae. Like many airgills, gillywogs, and some tailtube worms, this group has a soft, non-sclerotized exoskeleton composed solely of an elastic chitin-protein matrix. In most species, only the mouthparts remain sclerotized to aid in feeding, with the rest of the body relying on hydrostatic forces to maintain its integrity. This structure has a variety of benefits; some arthropods use their soft bodies to squeeze into tight spaces where they otherwise couldn't fit, while others benefit from the decreased growth time and energy cost, and a few, like the gummygrubs, have even morphed their squishy exteriors into novel body parts. All members of this subfamily possess prolegs on the thorax, allowing them to "walk" in ways no other Apterran animal can. These are formed from simple projections of the soft cuticle, inflated and moved with hydraulic pressure, and in many cases tipped with highly specialized bristles that also aid in locomotion. Most are either folivores or generalistic detritivores like the ancestral airgills, though one aberrant branch has adopted a completely unrecognizable lifestyle. They all share a common ancestor that lived during the Ice Age and began radiating into the modern genera almost immediately afterwards.

The most basal of the living gummygrubs are called Bristlecrawlers (Reptotrichus). They showcase a variety of features that were present in the first gummygrubs, but which have subsequently been lost in some of the more derived groups. For example, they have one pair of bristle-tipped prolegs on the thorax and every segment of the abdomen. These bristles end in sticky pads, allowing bristlecrawlers to more effectively cling to objects as they climb or walk. Like many generalists in the neotenic clade, they have relatively simple mouthparts derived from those of the mosquito larva. These are used for eating fungi, rotting plant matter, and occasionally carrion. Whatever their meal may be, bristlecrawlers aim to eat as much easily accessible material as possible; unlike Dermestimimid woodlice, with which they often share meals, they don't have any adaptations to get at tough or hard-to-reach scraps of food. To ensure they get enough food to last until their next meal, Reptotrichus possess another ability, in this case one that all their subfamily members have also retained: their soft bodies allow them to eat several times their own mass of food in a single sitting. In hard times, they can live off their reserves for months, but more often a large meal means an opportunity to grow. Unlike insects that mature into distinct adult forms, gummygrubs and numerous other neotenic mosquitoes have no upper limit on the number of times they can shed their exoskeletons. They simply shed their skin and grow a bit larger whenever the opportunity presents itself, with no maximum size aside from that imposed by food availability and structural integrity.

The next group of gummygrubs are called Gillopods (Caudocrus). These insects can be found anywhere from ground level to the tops of the tallest trees, but they are most common along the trunk and in the lower layers of the canopy. They are mainly scavengers of small creatures killed by Scansoriarthriform woodlice in defense of their trees. Such a diet puts them at odds with the woodlice, who would rather use the corpses as fertilizer to rebuild their home's strength after a battle. Gillopods, despite their gelatinous appearance, have ways of avoiding retaliation. First and most simply, they never bother the isopods directly, trying their best to remain inconspicuous at all times. They reduce their scent by constantly licking themselves clean using their labium and maxillae. However, these strategies are not enough to allow gillopods to remain undetected indefinitely. Luckily, their namesake trait affords them another chance to save themselves.

Unlike all other gummygrubs, which greatly reduced the size of their gills when they became more terrestrial, gillopods have co-opted theirs into an escape strategy. Stiff, sclerotized, and useless for respiration, these organs are now used much like the furcula of springtails. In most species, they are tucked under the body when at rest, but at the first sign of trouble, they rapidly swing into a back-facing position, in the process propelling their owner off whatever surface it was previously sitting on. This is the extent of their function in, for instance, the Sap-Lapping Gillopod (C. incisor), which has taken advantage of its ability to quickly flee a tree, becoming bolder and supplementing its diet with the sugar-rich sap of palm-grass trees. Though all trees on Apterra have some level of toxicity in their xylem and phloem, sap-lapping gillopods mitigate the risk by holding their meals in their stomach for many weeks before digestion begins, giving symbiotic bacteria a chance to break down many of the tree's insecticidal chemicals.

Other gillopods have stumbled upon secondary uses for their gill-furcula, as they are relatively easy to repurpose for other styles of movement. One such case is the Walking Gillopod (C. erectus), which stands with a tripodal posture using the tips of its gills and stiff proleg bristles as supports. It can thus inch itself along at a speed more comparable to mid-sized isopods and dipterachnids than to the slow, worm-like crawling typical of airgills. Another upright species is the Jumping Gillopod (C. altus), which has sacrified some of the strength of its gill muscles in exchange for greater precision. This allows it to make targeted leaps from one branch to another. In both these species, the pads of the thoracic proleg bristles are covered with microscopic barbs, lacking the adhesive properties of bristlecrawlers and sap-lapping gillopods. This lets them quickly latch onto and then let go of the surface they're traveling along. It also has the added benefit of not leaving behind a detectable trail for Scansoriarthriform pill bugs and other predators to follow.

Dermopods (Dermopodus) are the most derived and diverse genus in this subfamily. Most have entirely lost their bristles, and their prolegs have become two-pronged so each segment functionally possesses two pairs. Their mouthparts betray their more dedicated folivorous diet, with a beak-like labrum for securing a hold on a leaf and a pair of sharp mandibles for cutting chunks out. Members of this genus may be heavily specialized for a single plant species, on which they live their entire lives. Others are opportunistic, eating a little bit of many different plants. The Flower Dermopod (D. saccharinus) lies somewhere in the middle; it eats the flowers of a wide range of sweetstalks, consuming nectar, petals, pollen and all. The Field Dermopod (D. poaphagus) does not devote itself to any particular clade of grasses, but it does stick almost entirely to dry, nutrient-poor turfgrasses, basket-grasses, and other plants that few other insects bother with. Though these offer little energy, the field dermopod can still get enough calories because of its soft exoskeleton; every day, it eats four to six times its own dry weight in grass blades, allowing its abdomen to expand into a miniature fermentation chamber.

Two strange dermopod species, despite occupying vastly different niches and opposite ends of the size spectrum, are nonetheless each other's closest relatives. The only visible feature that unites them is the fact that, unlike all other members of their genus, both retain modified versions of the proleg bristles common to their family. The first is the Tree Dermopod (D. spinatus), the biggest and most well-defended of all gummygrubs. Its back is studded with barbed bristles designed to break away and remain stuck in the body of any creature that tries to touch their owner. It needs this deterrent because its main diet is the leaves of palm-grasses. Without wings, a massive body, or a gill-furcula to keep safe, it must rely solely on offensive tactics to avoid being killed by arboreal woodlice. This aggressive airgill repels attacks with claw-like proleg bristles sharp enough to pierce the bodies of much more armored arthropods, and its jaws can make short work of any isopod that tries to attack it head-on. Even its siphon is modified into a blade-like weapon that can cut apart enemies held in its claws. With each tree dermopod weighing up to fifty grams on a full stomach, it takes nothing short of a full-on assault by multiple Scansoriarthriform species to clear out an infestation. Because this would represent such a massive energy investment to avoid relatively minor damage, adults are simply left alone as long as they remain in low numbers. Young, on the other hand, are killed in massive numbers, as each female can produce ten thousand offspring in her lifetime.

The sister species to the tree dermopod is the Hematophagous Dermopod (D. venulensis), Apterra's first species of endoparasitic insect. It infects large warm-blooded animals, growing about a centimeter long. The end of its siphon lies flush with the surface of the host's skin, allowing it to get oxygen from outside. Meanwhile, its head gradually burrows into its host's flesh until it finds a small vein. It makes a tiny incision through which it inserts its entire head, drinking from the free-flowing blood for a few hours at a time before the vein begins to heal. After a few days of dormancy and waiting for inflammation to go down, it repeats the process, ultimately taking between five and twelve blood meals before reaching reproductive size. By this point, the dermopod is much too big to exit through the tiny hole it originally dug into its host's skin. It won't need to, though, because its mate lives alongside it. Male and female D. venulensis pair off before finding a host, then mate inside their fleshy nuptial cavity when both have reached a large enough size. Next begins a very strange form of pregnancy common among neotenic mosquitoes outside the derived scuttleworm-leechelet clade. Lacking an ovipositor or any other means of laying its eggs, the female dermopod retains them in its body as they develop. When they hatch, they simply eat their way out of their mother's body. In most species, the offspring take care to cause as little damage as possible, finding the quickest, least-destructive route to the outside world. Hematophagous dermopod young, on the other hand, completely devour both their parents in a feeding frenzy that results in exquisite pain for their host, which soon begins to scratch desperately at the site of the feast. This is often enough to liberate the now well-fed baby dermopods from their parents' home. If not, they will once again chew their way to freedom. They can then either re-infect the same host, sit on its skin until it brushes against a conspecific, or drop off to wait on a blade of grass to potentially spread to an entirely new host species. The chosen method is generally dependent on population density; when competition is high, newly-emerged hematophagous demopods are more likely to try for a new host.