What type of animal is black and string-like and can twist into strange shapes?
It’s an adult horsehair worm, sometimes known as a Gordian worm, because it can twist itself into shapes reminiscent of the Gordian knot in Greek mythology. Sometimes the worms are found clustered together in tangles of hundreds or even thousands. They’re members of the strange and wonderful phylum Nematomorpha, a group of parasites whose life cycle is still not entirely understood among scientists.
What is known is that nematomorphs reproduce sexually, laying millions of eggs in long, gelatinous strings around aquatic vegetation near the shores of ponds, streams, and lakes. Once hatched, the larvae embark on an amazing journey. Ingested by another larva (such as that of a mosquito or midge), the worm larva forms a cyst that can survive through the host’s metamorphosis into an adult insect. When the insect host is finally eaten by, say, a cricket or grasshopper, the cyst dissolves and the horsehair worm larva matures into an adult worm. A clever manipulator, the adult then uses chemicals to make its current host feel “thirsty” and go towards water – whereupon the worm emerges through the host’s body and becomes a free swimmer. (Surprisingly, the host insect often survives.) Adult horsehair worms don’t feed; their sole purpose is to find a mate and start the cycle all over again.