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True Bees — Part 13

The so-called solitary ants, of the family Mutillidae, are very common in portions of the United States. Most of them are clothed with hair, which is frequently bright-colored--in some of them being bright red--and on account of the velvety appearance which this hair gives them they are sometimes called velvet ants. In this group there is admirable opportunity for the study of life histories, since comparatively little is known about the way these insects live. They are no doubt parasitic in the nests of bees, and in Europe one species is known to live in the larval state feeding upon the larvae of a bumblebee. Schwarz, in this country, reared one of them from the cells of a burrowing bee, Riley another from the cells of another burrowing bee, and Davidson from an anthophorid bee.

Many strikingly beautiful insects belong to the family Chrysidiae. They are called cuckoo flies by the English writers, and goldwespen, or gold wasps, by the Germans. The colors are usually brilliant metallic green or blue, and the abdomen is frequently tipped with red. The larger species reach the length of half an inch or more, but the commoner forms in the United States are small insects, seldom reaching three-eights of an inch in length. They are rather stout-bodied insects, and are readily distinguished from the slender wasps of the preceding groups.

Careful studies of the economy of any of our North American species are greatly needed. Walsh reared Chrysis coerulans from the cells of one of the potter wasps (Eumenes fraterna), and Ashmead has seen one of them entering the burrows of a Trypoxylon, while he reared two species from the cells of a mud-dauber and one from the cells of an Odynerus. They are, therefore, either parasites or guests in the nests of wild bees and wasps, and are probably parasites rather than inquilines. In Europe some species of the genus Cleptes are true parasites on saw-fly larvae. There is a curious confusion sometimes in an Odynerus cell, for a Trypoxylon will enter one carrying its own store of food with it, and closing the entrance against the return of the female Odynerus; then comes along a Chrysis and lays an egg, from which hatches a larva which devours the stores of the Trypoxylon. The larva of the cuckoo fly is said to transform without cocoon to a pupa, and in this state to pass the winter.

The parasitic family Bethylidae, which Ashmead has transferred from the Proctotrypoidea to the Vespoidea, is a group of small insects. The family Trigonalidae, now placed here, but formerly placed near the Ichneumon flies, is also parasitic; they live parasitically in the nests of Polistes and Vespa, agreeing in habits with the Sapygidae.

The Bethylids are all, so far as we at present know, parasitic upon caterpillars and upon beetle larvae, usually upon very small larvae. Haliday, the Irish entomologist, many years ago, wrote an interesting account of the parasitism of some little Tineid larvae by a species of Bethylus; but in this case the parasite was observed to drag its little caterpillar victim into a hole in a reed. Possibly this fact had much to do with the original suggestion, which came from Haliday, that the Bethylidae should be placed nearer the wasps than with the true parasitic Hymenoptera. In the typical life history which follows, however, we will see that members of this family are true parasites.

Typical Life History

As has just been shown, the habits of the insects of this great group are so diverse that no one life history could be considered as in any way typical of the whole group. As a matter of fact, the proper and complete study of no one American species has as yet been made. Many of these insects are everywhere to be found, and life histories of surpassing interest and of much novelty await the first careful person who will care to devote the necessary time to this study. Of course a great deal is known about the general economy of our social wasps and interesting studies have been made by the Peckhams and others on some of the solitary wasps which belong to this super-family, as well as to the Sphecoidea; but it is the parasitic forms, especially of the Scoliidae, Myzinidae and Tiphiidae, which offer great opportunities. So do especially the Mutillidae and the Chrysididae. Of one of the Bethylidae, I am fortunately able to give some account, since it has been studied with care in my laboratory by Mr. August Busck, from whose unpublished notes the following interesting story is drawn.

Life History of a Parasitic Wasp

(Loelius trogodermatis Ashm.)