Of the fungi found on animal substances, none are more extraordinary than those species which attack insects. The white mould which in autumn proves so destructive to the common house-fly may for the present be omitted, as it is probably a condition of one of the _Saprolegniei_, which some authors include with fungi, and others with algæ. Wasps, spiders, moths, and butterflies become enveloped in a kind of mould named _Isaria_, which constitutes the conidia of _Torrubia_, a genus of club-shaped _Sphæriæ_ afterwards developed. Some species of _Isaria_ and _Torrubia_ also affect the larvæ and pupæ of moths and butterflies, converting the whole interior into a mass of mycelium, and fructifying in a clavate head. It has been subject for discussion whether in such instances the fungus commenced its development during the life of the insect, and thus hastened its death, or whether it resulted after death, and was subsequent to the commencement of decay.[H] The position in which certain large moths are found standing on leaves when infested with _Isaria_ resembles so closely that of the house-fly when succumbing to _Sporendonema Muscæ_, would lead to the conclusion that certainly in some cases the insect was attacked by the fungus whilst still living; whilst in the case of buried caterpillars, such as the New Zealand or British _Hepialus_, it is difficult to decide. Whether in life or death in these instances, it is clear that the silk-worm disease _Muscardine_ attacks the living insect, and causes death. In the case of the _Guêpes végétantes_, the wasp is said to fly about with the fungus partially developed.