Fig. 366.—Bracon palpebrator, female. Europe. (After Ratzeburg.)
Fig. 367.—Diagram of wing of Ichneumonid (A) and of Braconid (B). 1, 2, 3, 4, series of cells extending across the wing; a, b, divided cell of the Ichneumonid wing, corresponding with a, the undivided cell of the Braconid wing.
The Braconidae are the Ichneumones, or Ichneumonides, adsciti of the older Hymenopterists. They are extremely similar to the Ichneumonidae, but the hind body has a much less degree of mobility of its segments, and there are some constant distinctions in the wings. Although there is a great deal of difference in the various forms of each of the two families, yet there are two points of distinction easily appreciated; the series of cells running across the wing (Fig. 367) being only three in the Ichneumonides (Fig. 367, A), but four in the Braconids (Fig. 367, B); besides this the space a of the Braconid wing is divided into two (a, b) in the Ichneumonid wing. A glance at these characters enables us at once to separate correctly the thousands of species of the two families.
The habits of the Braconidae are similar to those of Ichneumonidae, it being believed that all are parasites. Usually they attack larvae, but they are bred in great numbers from pupae, and even from imagos of other Insects. Elasmosoma is one of the few parasites known to attack ants. As many as 1200 specimens of Microgaster have been reared from a single Lepidopterous larva. Although such parasitism raises a feeling of repulsion, yet there is reason for supposing that there may be little or no cruelty or acute suffering connected with this mode of life. The victim attacked is not eaten, the parasites in the interior taking in the lymph of the caterpillar either by the mouth or by endosmosis, but not biting their host. The latter displays no sign of sickness, but eats voraciously, so that it serves merely as a sort of intermediary between the juices of the plant and the larvae inside itself. It is only when the metamorphosis is at hand that the host sickens, but this does not always happen: parasitised larvae frequently change to pupae, and they may occasionally even become perfect Insects. Cases are known in which imagos have appeared with some of the small parasites embedded in some of the outer parts of their bodies. These cases are, however, very rare; in the enormous majority of instances the host is destroyed either when it is in the larval stage or before the pupa has advanced to any great extent on its metamorphosis to an imago. Particulars as to various species will be found in the valuable work of Ratzeburg we have already referred to.[[477]] Reference may also be made to Goureau's account of Microgaster globatus,[[478]] this latter including some suggestions by Dr. Boisduval on some of the difficult physiological questions involved in the lives of these parasites.
Fig. 368.—Stalked cocoon of Apanteles formosus. (After Marshall.)
The metamorphosis of Microgaster fulvipes has been studied by Ratzeburg, and an epitome of his observations is given by Marshall.[[479]] The larva goes through a series of changes somewhat similar to those we have already sketched in Anomalon circumflexum. Usually these Insects after emerging from the body of their host spin a mass of cocoons more or less loosely connected together. A most curious case has, however, been recorded by Marshall[[479]] of a stalked cocoon (Fig. 368) being formed as an exceptional act by Apanteles formosus. Mr. Marshall has recently received other specimens of this cocoon as well as the Insects reared therefrom in France, and inclines to the opinion that the stalked cocoon may be the usual form, and is sometimes departed from by the Insect for unknown reasons.
This family is of enormous extent; we have several hundred species of it in Britain,[[480]] and there are no doubt many thousands of undescribed exotic forms. To Apanteles glomeratus we are indebted for keeping our cabbages and kindred vegetables from destruction by the caterpillars of the white butterflies. The larvae of the various species of Pieris, as well as those of other Lepidoptera, are attacked by this little Insect, the masses of whose cocoons may frequently be found in numbers in and near cabbage gardens. The tropical species of Braconidae are greatly neglected, but many large and remarkable forms—some of brilliant colours—have been brought from there, so that we are justified in believing that Insects of this family will prove to be very numerous. There are but few apterous Braconidae. Both sexes of Chasmodon apterus are destitute of wings; the females of one species of Spathius, and also those of Pambolus and Chasmodon are apterous; in a small number of species of various genera the wings are so minute as to be incapable of serving as organs of flight. In the genus Alloea the wings of the male are shorter than those of the female.
