An arthropod believed to be indigenous to Heshtok. It nests beneath the skin of other animals, and produces highly adaptive toxins that can have powerful but temporary effects on a range of alien body chemistries, driving hosts to engage in high-risk or aggressive activities as a means of finding new hosts. Combined with their potential to produce many larvae over their three-week lifecycle, they can spread quickly through densely populated settlements. A mature Skindiver can reach up to 2.5 centimetres in length.

Several years after the Reaper War, colonies of the parasite were reported throughout the Crescent Nebula, in the wake of increased relay traffic from the Nemean Abyss, originating in the newly reopened Shrike Abyssal.

Said Dr. Nen Burtan of Felis General Hospital's Exobiological Assessment Wing:

"It was inevitable that the increase in traffic from these areas - areas where living conditions have deteriorated, and medical supply has been greatly substandard - would lead to increased risk. We have been working to prepare for eventualities just like this. The creatures are moderately dangerous, but only in large numbers. This is cause for caution and diligence, not alarm....The creature is quite adaptable. It seems to prefer salarians, but we've found them in asari, humans, batarians, elcor and - of course - vorcha. This isn't Clan of the Hollow; the personality changes are minor and higher functioning isn't impaired. But we must act to contain this. Given the adaptability of Heshtokian life, it would be wise to monitor the situation closely and be on guard for mutations".

Over 450 infestations were reported within three weeks, on nine planets.

Eventually, at least one case reached the Citadel, in the form of an infected duct dweller.