it has been found that " arthrobotrys oligospora", a net-building species of fungus, can detect the presence of nematodes nearby in the soil and only builds its snares when they are present. this is presumably because building the net is a highly energy-consuming process; the fungus is alerted to the presence of the nematode by detecting the pheromones, such as ascarosides, with which the worms communicate. the fungus takes active steps to attract its prey by producing olfactory cues that mimic those used by the worm to find food and attract mates. "arthrobotrys dactyloides " is a species that employs a loop of hypha to catch nematodes; when one tries to pass through the ring, the loop constricts with great rapidity, trapping the prey.