Caterpillar Fungus, Or Fungoid Parasites, a name given to many species of fungi which attack various insects, especially the larva) of beetles and moths, filling out their bodies, and sending out shoots into the air, so that the animal looks as if transformed into a vegetable. They have been generally described in works on botany, the plant portion having attracted the most attention. Mr. G. R. Gray has specially described the insect portion, taking them up in the usual order of entomological systems. These parasitical plants or fungi infest insects of all orders, and in the larva, pupa, and perfect states; some, however, are from their habitats peculiarly exposed to these growths. The beetles, many of which in all their stages live in the ground, amid decaying vegetable and animal matters, are very liable to these attacks; the growth, no doubt, begins internally, as specimens have been found in which the fungus was just bursting forth from some part of the body; the most usual place for the fungus to appear is from the pectoral surface of the thoracic segments; the larva) usually lie upon that side, and are generally found dead, and either decayed or dried up; one parasite is ordinarily all that is found on one larva, but two, three, or more are occasionally found.
The diurnal lepidoptera have not been seen infested with fungi or moulds, while the nocturnal ones are very much affected; the muscardine, which destroys great numbers of the silkworm, belongs to this class of vegetable parasites. Among orthoptera, the mole cricket; among hymenoptera, ants, bees, wasps, and hornets; among hemiptera, the cicadae; and among diptera, the flies, are often seen more or less covered with a delicate mould or fungus, which bursts out between the segments of the body, and sometimes grows with great rapidity. From numerous observations, it is certain that life is not extinct when the insect becomes the basis of the parasite. Most of the insects thus affected are vegetable feeders, and it is generally admitted that the spores or seeds of the fungus are swallowed with the food, and that the seeds do not become attached to the exterior of the body .and thence penetrate to the interior; some believe that the seeds may also gain admission by the tracheae or breathing apparatus. These spores are so exceedingly minute as to appear like smoke in the air, and Fries has estimated above 10,000,000 in a single plant; their minuteness, however, is not so wonderful as that each contains the elements necessary for germination.
However admitted, the seeds begin to germinate, gradually grow if the circumstances are suitable, and till the animal completely with the thallus; the insect retains its external form, though internally its fluids are dried up by the growth of the fungus; the plant then forces its way through the skin at various places, through the articulations, and even through the hard surface of the head. It may be that the vegetable growth does not always depend on its being nourished by the fluids of the insect; but that the latter, enfeebled by the heavy rains that fall periodically in the intertropical regions, where these growths abound, receives the seed, which grows by the influence of external moisture, and by its thallus interferes mechanically with the functions of the insect, and finally destroys it. A vigorous larva might even devour the parasitic seed, which, not finding a suitable nidus, might be voided in the usual way. These growths vary in length from a mere protuberance to 10 inches, and in diameter from a fine hair to one fourth of an inch. Most of them belong to the old genus sphmria, which has been subdivided into many genera, which, with many other apparently very different forms, may be more or less immature growths of totally dissimilar described genera.