Nematoda is a speciose phylum occupying most environmental habitats, from alpine grasslands to marine sediment, as well as colonising plants and animals, including 43 945 known vertebrate hosts. Some 23 000 nematode species have been described but it is estimated that the phylum comprises up to 1 million species .The best known species is Caenorhabditis elegans, a free-living nematode, the first animal to have its whole genome sequenced, and an extensively used model organism .A notable feature of the phylum is parasitism, which has arisen independently across the various phylogenetic clades and has resulted in the average mammalian or avian host harbouring at least three parasitic nematode species .Infections cause an enormous impact on human, animal, and plant health, with gross medical, social, and economic repercussions; for instance, annual crop production losses are estimated to be between 8.8% and 14.6%, and it has been estimated that approximately 1.45 billion people are infected with at least one soil-transmitted helminth (STH)
Despite the high prevalence of nematodes in the environment, and as parasites, it is perhaps surprising that we have such incomplete knowledge on how nematode eggs hatch. From our review of the existing literature, the huge diversity of requirements and triggers for the complex regulated process of hatching across the phylum Nematoda is clear. It is also evident that there are still many gaps in knowledge of this important aspect of nematode biology, particularly with regard to animal parasites key to human and livestock health. New technological advances offer some help in completing the picture of the genetic and molecular basis of the hatching cascade. An example of this can be seen in research on G. rostochiensis, where detailed past observations combined with new data from high-throughput techniques are informing not only fundamental knowledge but also new control approaches, such as suicidal hatching and hatching inhibitors. The extent to which these control strategies can be adapted to other parasites, such as the STHs, remains to be seen but is an exciting possibility .In the quest for inducers and mechanisms of hatching, advanced models recapitulating the parasite niche in greater detail such as gnotobiotic animals and organoids could prove instrumental. To really capitalise on those models, advances in tools to generate mutant worms will enable the study of the function of genes of interest identified in genomic studies of parasites. Understanding hatching promises to be both fascinating and invaluable, presenting an opportunity to investigate how specificities in hatching requirements relate to parasitic nematode evolutionary survival strategies, and how manipulating the hatching process can control the impact of parasites to human and agricultural health.