Early Dutch contributions to the knowledge of Ephemeroptera or Mayflies In the first half of the seventeenth century three Dutchmen studied a remarkable insect, the day-fly. They were the apothecary Joannes Dortman (? - ca. 1625), the physician Outgert Cluyt (1577-1636), and the minister Johannes de Mey (1617-1678). Dortman is the first to identify the legendary ‘ephemeron’ of .Aristotle with a concrete living insect that he also called 'ephemerum’. In a few words he describes its appearance and behaviour, and points out that it originates from a ‘worm’ (larva). He illustrates the insect in a woodcut. Dortman's account is published by Outgert Cluyt, who inherited his papers, together with the results of his own investigations, after he had tried to get. both from books and from nature, a deeper understanding of the animal he preferred to call ‘hemerobius’. His observations from nature he obtained, for the greater part, from reliable ‘men on the spot’, anglers and fishermen, by means of a questionnaire. In this way he manages to add considerably to the knowledge of the animal’s appearance and structure, its behaviour, and above all its origin from a larva. Its life-cycle he considers. wrongly, to be identical with that of the much better known silkmoth. Though not perfect, his illustrations are much better than those of Dortman. In an appendix to Goedaert’s entomological studies, Johannes de Mey mentions a species of Ephemeroptera he observed near Dordrecht, adding nothing substantial to the information already gathered by Cluyt. Yet, he is important as an advocate of the hitherto neglected studt of ‘the smallest and least regarded creatures of God’, that of entomology. Characteristic of the three Dutchmen is that they do not longer accept the authority of the written records alone, bul consciously use their experience to emend and augment booklearning. It is for this reason that the unpretentious booklet by Cluyt (De hemerohio, 1634) may be the earliest scientific monograph dedicated to a single insect. In a ...