The hairworm is a long, thread-like parasite that sits bundled up inside the body of its host.
It grows so large that it takes up most of the room inside the host’s body, waiting for the right moment to come bursting out. But that is not the scariest thing about the parasite, because it can also survive a deep freeze (at -70°C) and go on to infect its favourite hosts, some insects and crustaceans.
The adult hairworm (in the phylum Nematomorpha) is aquatic but in many species the worm develops inside land-loving insects. To ensure it does not dry up when it escapes from the innards of its host, it uses its first trick to manipulate the host. When the time has come for it to make an exit, the hairworm is able to tamper with the brain of its host (usually a cricket) and persuade it to seek out water, where the adult worm can escape and reproduce.
But the hairworm has a complex life cycle and the cricket is not the only host that it infects throughout its life. Before it gets into a cricket, this parasite starts out as an egg that hatches into a free-swimming larva, which then needs to infect an aquatic invertebrate, such as a snail or mosquito larva, to reach its next stage of development as a cyst. It then needs to be eaten by its final host - the cricket - where it matures into a long, thin worm, many times longer than the length of its host.
This process of getting into each of those hosts and waiting to encounter the next one may end up being dragged out over the course of an entire year. For hairworms that live in temperate regions of the world, the parasite is faced with a dilemma - there is a good chance that before it is able to end up in a cricket and develop into an adult worm, winter will arrive and everything will start freezing over.
But the hairworm Paragordius varius is not at all bothered by snow, ice and freezing conditions - it simply shrugs it all off and waits it out. In fact, arecent study showed that it can tolerate being frozen at -30°C or even -70°C for weeks. When it thaws out, it is still fully capable of infecting the next host.