Fig. 306.—Presumed larva of Nemoptera (Necrophilus arenarius). After Roux. Pyramids of Egypt.
The Nemopterides are a small group of delicate, graceful Insects. About thirty species are known. Knowledge of the group is still very imperfect. A larva has been found of a most remarkable nature that probably belongs to it; it was described under the name of Necrophilus arenarius, and considered to be a fully-developed Insect. This larva occurs in the tombs and pyramids of Egypt where sand has accumulated. The perfect Insects of the genus Nemoptera are, however, found in open places amongst bushes, and flit about in a very graceful manner. Several species are found in Southern Europe and the Mediterranean region (Fig. 305, N. ledereri), but none come so far north as Central Europe. Formerly the genus Nemoptera was considered to be allied to Panorpa on account of the beak-like front of the head. The parts of the mouth are, however, different from those of Panorpa, and it seems more probable that if the Nemopterides have to be merged in any of the divisions of Hemerobiidae, they will be placed in Chrysopides or Osmylides. The species of the sub-family were for a long time believed to be peculiar to the continental regions of the Old World, but a species has recently been discovered in Northern Chili.[[393]]
Sub-Fam. 4. Mantispides.—Prothorax elongate; the raptorial front legs inserted at its anterior part.
The members of this small group are readily recognised by the peculiar structure of the front legs; these organs resembling those of the Orthopterous family Mantidae, so that the earlier systematic entomologists, deceived by this resemblance, placed the Mantispides in the Order referred to.
Fig. 307.—Mantispa areolaris. Brazil. (After Westwood.)
The Mantispides possess four membranous wings, either sub-equal in size or the posterior pair smaller than the front pair and not folded; the veins of these wings are rather numerous, as are also the cells they form; there is considerable difference amongst the species in this latter respect, owing to the transverse veinlets differing in their abundance. The antennae are short, not in the least thickened at the tip. The head is not produced into a beak. The anterior legs, placed quite at the front part of the thorax, have the coxae very long; the femur is somewhat incrassate, and is armed on one side with spines; the tibia is shaped and articulated so as to fold closely on to the spines, and to thus constitute a formidable and perfect prehensile organ, the tarsus being merely a small appendage.
Fig. 308.—Mantispa styriaca. A, Larva newly hatched, or first form; B, mature larva. (After Brauer.)
Only a few species of Mantispa are found in Southern Europe; but the group has representatives in most of the warmer regions of the world, and will probably prove to be rather numerous in species. The front legs are used for the capture of prey in the same way as the somewhat similar front legs of the Mantidae. The transformations have been observed by Brauer[[394]] in the case of one of the European species, M. styriaca. The eggs are numerous but very small, and are deposited in such a manner that each is borne by a long slender stalk, as in the lacewing flies. The larvae are hatched in autumn; they then hibernate and go for about seven months before they take any food. In the spring, when the spiders of the genus Lycosa have formed their bags of eggs, the minute Mantispa larvae (Fig. 308, A) find them out, tear a hole in the bag, and enter among the eggs; here they wait until the eggs have attained a fitting stage of development before they commence to feed. Brauer found that they ate the spiders when these were quite young, and then changed their skin for the second time, the first moult having taken place when they were hatched from the egg. At this second moult the larva undergoes a considerable change of form; it becomes unfit for locomotion, and the head loses the comparatively large size and high development it previously possessed. The Mantispa larva—only one of which flourishes in one egg-bag of a spider—undergoes this change in the midst of a mass of dead young spiders it has gathered together in a peculiar manner. It undergoes no further change of skin, and is full fed in a few days; after which it spins a cocoon in the interior of the egg-bag of the spider, and changes to a nymph inside its larva-skin. Finally the nymph breaks through the barriers—larva-skin, cocoon, and egg-bag of the spider—by which it is enclosed, and after creeping about for a little, appears in its final form as a perfect Mantispa. Thus in this Insect hypermetamorphosis occurs; the larval life consisting of two different instars, one of which is specially adapted for obtaining access to the creature it is to prey on. It should be noticed that though this Insect is so destructive to the young spiders, the mother spider shows no hostility to it, but allows the destroying larva to enter her bag of eggs without any opposition; she appears, indeed, to be so unconscious of the havoc that is going on amongst her young that in one case she continued to watch over and protect the egg-bag in which the destruction was taking place during the whole of the period of the larval development and half the period of pupation of the Mantispa.