Unlike Earthly megarhyssae, these sophonts have a heavily female-skewed (or more properly ažaras-skewed) sex distribution, and their slender, elegant bodies stretch some 10’ 8½” (3.26 m) long with antennae, and 6’ 6” (2 m) long without, on average. Female megarhyssae's ovipositors are at least half again as long as their bodies, and often twice or more as long; they are tipped with metal, often zinc, and incredibly sensitive. They can stand up on their rear legs, using their tail and ovipositor for balance; in this pose, they stand 5-6 feet (152-183 cm) tall. Binary male megarhyssae average 8’ 3½” (2.52 m) long with antennae, and 6 feet (1.84 m) long without. Both sexes stand about 3’ 3” (1 m) tall at the shoulder.

Other than size and ovipositor presence or absence, the two sexes can be differentiated by antenna color (female yellow, male brown), as well as by males having more yellow coloration than females, including a raised yellow spot beneath each forewing.

Their mouthparts include a labrum with a long row of thick spines along the outer edge, maxillae, and mandibles with two teeth. Their thoraces have spiracles that run along their entire length. Their legs are covered with tiny hairs or spines, and their wings (a pair of fore- and hindwings that lock together during flight, as well as a pair or tiny basal wings) are visibly covered in numerous veins and cells.

Megarhyssa-taurs are known to exist, with their lower bodies being slightly larger than normal to accommodate the humanoid upper body in place of the head; they often result from oviposition into strong-willed individuals, usually safìr or less often human. Taurs have megarhyssan antennae on their foreheads and fore- & hindwings on their backs, sometimes in addition to another two pairs of wings on the insectoid thorax. Only some taurs have standard megarhyssan reproductive organs, but they all have safìroid ones.

Megarhyssa ovipositors, in addition to being used to deposit eggs on the crew of the ships they capture, can also be used as stingers, injecting venom into the target. They can control the composition of their venom, and concoct several different vena at will, all of which are fiendishly complex, littered with polydnavira endogenous to the individual megarhyssa, and ever evolving to avert the development of natural antivena; megarhyssae will often deploy aphrodisiac formulae when courting others. Megarhyssa venom can be incredibly potent, with a single bubble's worth of some formulae being able to incapacitate a dragon.

When deploying venom, megarhyssae produce orders of magnitude more of it than the relevant glands can hold, requiring them to use their bubble as a holding chamber, whereupon it inflates into a sphere instead of a flat circle; this often requires them to discard unused venom by “spraying” it out of their ovipositors.

Megarhyssae are immune to their own vena, and have been seen contorting their bodies to drink from their ovipositors-turned-stingers; the purpose of this ritual is unknown. It takes a megarhyssa anywhere from several hours to several days to be able to produce new venom, depending on the desired formula. Some megarhyssae are capable of producing psionically (or, it is believed, even magically) potent vena; their shells are marked with blue, purple, or other exotic colors as a warning of this psionic power.

Some megarhyssae have two tails and, if female, two ovipositors.

Megarhyssae prefer to eat fruit, cereals, and root vegetables, as well as most any other starchy food; honeydew and sweet potatoes are particular delicacies to them. However, they are omnivorous in practice, especially after long stretches of privation.

Megarhyssae often, but don't always, mate as part of the process of Emergence from the substrate into which they were oviposited, at which point their life is considered to begin, as their larvae and pupae are nonsapient. Males tend to swarm the sites of female Emergence, detected by the chewing sounds they make as they eat through the substrate into which they were laid, and mating outside that event or immediately thereafter is rare. Virgin females lay haploid eggs, which will Emerge as their sons; mated females lay diploid eggs, which will Emerge as their daughters. Their eggs are ectoparasitoids, oviposited directly on the host, one egg per prey item. While still inside the eggs, the megarhyssae develop into larvae. Upon hatching, the larvae emerge and begin feeding on the host.

These wasps remain in their larval form throughout the winter, continuing to feed on their host meal. In the spring they pupate within the host burrow, undergo a complete metamorphosis, and Emerge as adults in the summer.

Mated megarhyssae are held in higher esteem, but a virgin can still earn respect through her own deeds and those of her granddaughters'. Virgin females stereotypically study magic, and dowagers (elderly virgins) are feared admirals & living libraries of sage knowledge and strategy, both their own & captive species'.

When a female Emerges, only the males of her clade will attempt to mate with her, while males of other clades will disperse. How males discern the clade of the Emerging female remains unknown, although there is speculation that it is an olfactory or chemoreception signal. Some megarhyssae of both sexes have been seen engaging in courtship displays post-Emergence by raising their tails, extruding four or six coremata (hair pencils) of similar length to a male's abdomen or a female's ovipositor, and antennating against those of the opposite sex; this is far more common in taurs, the reason for which is yet unknown.

Following copulation, females fly off to locate hosts and oviposit their eggs, while males will continue to search for Emerging females in their home range. Females will oviposit multiple times, even within the same day. Once a megarhyssa Emerges, she is in a race against time to oviposit all of her eggs before they hatch within her ovaries and consume her from the inside out; this has caused the species to turn to space piracy after the extinction of their original host species following a failed slave uprising.

While mating is often impersonal among megarhyssae, some mate for a term of years or for life, though such pairing is not usually known to impede the practice of casual sex with others; megarhyssae are known to engage in recreational sex, and non-courtship displays of their genitalia or coremata, with a casualness unmatched except perhaps by safìr.

The most fascinating aspect of the megarhyssan reproductive cycle is the ovipositing behavior of the adult female wasps. Once a female has successfully mated, she must first locate a host inside a suitable substrate, or place one there herself. Megarhyssae seem to prefer sapient and sophont prey. Exactly how females sense these hosts in a manner suitable for triggering an egglay trance is currently unknown, but experts speculate that it is either via olfaction or auditory cues, in both of which realms their sensory apparatus is particularly keen.

Female atratans have the longest ovipositors of any megarhyssa clade, ranging from about 22-26 feet (6.68-8.02 m) long, and can parasitize larvae burrowed up to 24 feet (7.36 m) in hardwood. A membranous pouch at the abdomen's tip holds the looped ovipositor while the female lays eggs. This provides support and stability while the stylus tip penetrates the wood.

The ovipositor is inserted straight down into the substrate so that it will eventually enter the prey item's burrow at an exact right angle. Females choose appropriate burrows for ovipositing so that the tip of the ovipositor will just reach the surface of the host.

Once the female is ready to oviposit her eggs, she rotates segments 8 and 9 of her abdomen and unfolds her intersegmentary membranes so that they form a disc or bubble, depending on the clade, 3½ feet (1 m) or more in diameter. The surface of this disc produces a lytic secretion that disintegrates wooden substrates and facilitates her ability to insert her ovipositor. After she lays her ectoparasitoid eggs on the surface of the prey item, she completes the same rotational movements to remove her ovipositor from the wood, and the stylus returns to its resting position.

Due to the long length of the ovipositor in female megarhyssae, completion of this cycle takes over one hour. During this period the females are particularly vulnerable to predators due to their egglay trance and physical anchoring to the substrate; therefore, the risk of predation is positively correlated with ovipositor length, and others will guard them during the process. Guardian megarhyssae usually stand in a high stance with their tails and ovipositors either raised straight up or curled under their bodies, ready to attack — and often charged with venom — in either case.

Megarhyssae, both standard and tauric, are space pirates who board starcraft and return them to their territory, thence to use the crew for incubation, as their original prey species are long extinct. Their own starcraft are notable for massive interior spaces and control surfaces meant to be manipulated by their mouthparts and/or ovipositors. Tauric megarhyssae are often leaders of their bands. Some bands are known to board ships and engage in superfluous courtship displays for the sole purpose of entrancing safìr with their pheromones and leading them back to their own craft.