Among those saw-flies whose larvae feed throughout life in a concealed situation, we find an interesting transition between the caterpillar and the legless grub.  For example, the giant saw-flies (so called ‘Wood-wasps’) have larvae that burrow in timber, and these larvae possess relatively large heads, somewhat flattened bodies with pointed tail-end, and very greatly reduced legs.  The feeble legless grub, characteristic of the remaining families of the Hymenoptera, is provided for in a well-nigh endless variety of ways.  The female imago among these insects is furnished with an elaborate and beautifully formed ovipositor, and the act of egg-laying is usually in itself a provision for the offspring.  Gall-flies pierce plant-tissues within which their grubs find shelter and food, the plant responding to the irritation due to the presence of the larva by forming a characteristic growth, the gall, pathological but often regular and shapely, in whose hollow chamber the grub lives and eats.  Ichneumon-flies and their allies pierce the skin of caterpillars and other insect-larvae, laying their eggs within the victims’ bodies, which their grubs proceed to devour internally.  Some very small members of these families are content to lay their eggs within the eggs of larger insects, thus obtaining rich food-supply and effective protection for their tiny larvae.  In Platygaster and other genera of the family Proctotrypidae, M. Ganin (1869) showed the occurrence of hypermetamorphosis somewhat like that already described as occurring among the Oil-beetles (Meloidae).  The larva of Platygaster is at first rather like a small Copepod crustacean, with prominent spiny tail-processes; after a moult this form changes into the legless grub characteristic of the Hymenoptera, among which larvae even approaching the campodeiform type are very exceptional.  The species of Platygaster pass their larval stages within the larvae of gall-midges.

Wasps, bees and ants, have the ovipositor of the female modified into a sting, which is often used for the purpose of providing food for the helpless grubs.  Thus the digging wasps (Sphegidae and Pompilidae) hunt for caterpillars, spiders, and other creatures which they can paralyse with their stings, and bury them alongside their eggs to furnish a food-supply for the newly-hatched young.  The social wasps and many ants sting and kill flies and other insects, which they break up so as to feed their grubs within the nest.  It is well known that the labour of tending the larvae in these insect societies is performed for the most part not by the mother (’Queen’) but by the modified infertile females or ‘workers.’  Other ants and the bees feed their grubs (fig. 18), also sheltered in well-constructed nests, on honey elaborated from nectar within their own digestive canals.  In all cases we see that the helplessness of the grub is associated with some kind of parental care.

[Illustration:  Fig. 19.  Larva of Gall-midge (Contarinia nasturtii), ventral view showing anchor process (a), and spiracles projecting at sides.  Magnified 30 times.  From Carpenter, Journ.  Econ.  Biol, vol.  VI.]