This fly, belonging to the genus Phora (Fig. 32, Phora incrassata; a, larva; b, puparium; c, another species from Mammoth Cave), is a small insect about a line and a half long, and found in Europe during the summer and autumn flying slowly about flowers and windows, and in the vicinity of beehives. Its white, transparent larva is cylindrical, a little pointed before, but broader behind. The head is small and rounded, with short, three-jointed antennæ, and at the posterior end of the body are several slender spines. The puparium, or pupa case, inclosing the delicate chrysalis, is oval, consisting of eight segments, flattened above, with two large spines near the head, and four on the extremity of the body.
When impelled by instinct to provide for the continuance of its species, the Phora enters the beehive and gains admission to a cell, when it bores with its ovipositor through the skin of the bee larva, laying its long oval egg in a horizontal position just under the skin. The embryo of the Phora is already well developed, so that in three hours after the egg is inserted in the body of its unsuspecting and helpless host, the embryo is nearly ready to hatch. In about two hours more it actually breaks off the larger end of the egg-shell and at once begins to eat the fatty tissues of its victim, its posterior half still remaining in the shell. In an hour more, it leaves the egg entirely and buries itself completely in the fatty portion of the young bee.
The maggot moults three times. In twelve hours after the last moult it turns around with its head towards the posterior end of the body of its host, and in another twelve hours, having become full-fed, it bores through the skin of the young, eats its way through the brood-covering of the cell and falls to the bottom of the hive, where it changes to a pupa in the dust and dirt, or else creeps out of the door and transforms in the earth. Twelve days after, the fly appears.
The young bee, emaciated and enfeebled by the attacks of its ravenous parasite, dies, and its decaying body fills the bottom of the cell with a slimy, foul-smelling mass, called "foul-brood." This gives rise to a miasma which poisons the neighboring brood, until the contagion (for the disease is analogous to typhus, jail or ship-fever) spreads through the whole hive, unless promptly checked by removing the cause and thoroughly cleansing the hive.
Foul-brood sometimes attacks our American hives, and, though the cause may not be known, yet from the hints given above we hope to have the history of our species of Phora cleared up, should our disease be found to be sometimes due to the attacks of such a parasitic fly.
33. Bee Louse and Larva.
We figure the Bee louse of Europe (Fig. 33 b, Braula cæca), which is a singular wingless spider-like fly, allied to the wingless Sheep tick (Melophagus), the wingless Bat tick (Nycteribia) and the winged Horse fly (Hippobosca). The head is very large, without eyes or ocelli (simple eyes), while the ovate hind-body consists of five segments, and is covered with stiff hairs. It is one-half to two-thirds of a line long. This spider fly is "pupiparous," that is, the young, of which only a very few are produced, is not born until it has assumed the pupa state or is just about to do so. The larva (Fig. 33 a) is oval, eleven-jointed, and white in color. The very day it is hatched, it sheds its skin and changes to an oval puparium of a dark brown color.
34. Hive Trichodes.