Chapter 15: Fungi Exploiting Microscopic Animals

The chapter presents at least eleven distinct predatory mechanisms that fungi have evolved, each representing a specialized approach to overcoming prey defenses and establishing parasitic infections. Motile strategies employ chemotactic swimming spores in chytrids and oomycetes that navigate toward host organisms before encysting and breaching the host cuticle. Projectile-based mechanisms include pressurized gun cells in genera like Haptoglossa that instantaneously inject needle-like penetration tubes through host tissues using hydraulic force. Adhesive capture employs sticky conidia and hyphal structures that physically attach to passing prey, as demonstrated in Verticillium, Meristacrum, and related genera. Ingestion-based predation involves curved spores that lodge within host digestive structures, establishing infections from within the esophagus or intestinal tract. Trap-forming fungi represent perhaps the most sophisticated predatory innovations, featuring adhesive three-dimensional hyphal nets that function analogously to spider webs, nonconstricting rings that detach and adhere to prey, and constricting rings capable of closing within milliseconds through rapid hydraulic expansion to strangle captured nematodes. Chemical attraction enhances predatory success, with fungi releasing volatile compounds such as ammonia and carbon dioxide that draw prey toward traps. The chapter extends beyond nematode parasitism to examine fungal exploitation of eggs, amoebae, rotifers featuring specialized structures termed lethal lollipops, tardigrades, and arthropods including springtails and collembola. Additional predatory mechanisms involve the secretion of paralytic toxins, exemplified by oyster mushrooms that immobilize nematodes while acquiring nitrogen from invertebrate tissues. The chapter concludes by addressing practical applications of nematode-trapping fungi in biological control of plant-parasitic nematodes in agricultural systems and gastrointestinal parasites in livestock, where chlamydospores survive digestive passage and function within fecal environments, establishing these fungi as naturally occurring control agents in terrestrial ecosystems.