National Geographic : 1929 Jul
INSECT RIVALS OF THE RAINBOW paralyzes it and then builds a crude cell around it, after attaching an egg to the grub. The larva of the wasp, hatching out, consumes the grub and then spins a cocoon in which it de velops. The species reproduced is: South American Burrowing Wasp (Campsomeris ephippium Say. Plate XI, figure 8), found in South and Central America. Horn-tail Family (Siricidae). This fam ily consists of about Ioo species, about one third found in America. Its members are mostly rather large, brightly marked, and well built. The adult female has an ovipositor con sisting of five pieces, the two outside ones forming a sheath, and two of the others being furnished at the tip with a series of fine, hard, transverse ridges arranged like the teeth of a file. With this she is able to match the work of a gimlet or auger in human hands, and can drill innumerable holes in the solid wood of a tree. In each of these she places an egg. The best-known of the horn-tails is the pigeon tremex, which is about one and one-half inches long, with a rusty head and thorax, and a black abdomen with yellow bands and spots. The female bores a hole half an inch deep into elms, oaks, sycamores, and maple trees. The larvae, hatching from the eggs laid therein, bur row into the heart wood where they grow into cylindrical, blunt-ended, whitish grubs, measur ing about an inch and a half in length. When ready to transform into an adult in sect, the grub makes a cocoon of silk and chips, and then goes to sleep. On awakening as a full-fledged pigeon tremex it bores out at right angles to the gallery dug by the grub, instinctively knowing that in such direction lies the shortest way to liberty. The European grain cephus, whose larvae bore into the stems of wheat and cause the straw to break about harvest time, belongs to the horn-tail tribe. About the time the head of the wheat begins to form, the fly bores a small hole in the straw. When the larva hatches from the inserted egg, it tunnels down the stem, and by wheat-cutting time has passed below the level of the cutter bar. In this way it remains in the stubble, where it makes a silken cocoon and hibernates. The species reproduced is: Common Horn tail (Trmecx columba Linn. Plate XI, figure I ), found all over North America. Cimbicid Family (Cimbicidae). The most familiar species of the group is the American Saw-fly. Its eggs are laid in June in crescent shaped slits made in leaves. The food plants are elm, birch, linden, and willow. When dis turbed the larva spurts a fluid from glands just above the spiracles. When it is full-grown it burrows in the ground, makes an oval, brown ish cocoon, and spends the winter there, not changing to a pupa until spring. It emerges in May or June. The species reproduced is: American Saw fly (Cimbex americana Leach. Plate XI, fig ure 12), habitat North America. Halictus Bee Family (Halictidac). Some of these bees are larger than a fair-sized wasp and some are smaller than a house-fly. Every halictus carries what has been called a clearly written certificate of her guild. It is a smooth, shiny line, or groove, on the last segment of the abdomen that acts as a guide for the sting. Some species build wonderful cells for their babies. The burrows in which these are located may be rough, but the cradles must be perfect. Leading from the burrow, the cells are ex cavated so as to resemble water bottles laid on the side. No human plasterer ever did a finer job than these bees. First there is a coating of clay, its surface roughened like the outside of a thimble. On this is laid a smooth coat, mixed with saliva and carefully troweled with the tongue-a glazing that is exquisite in its per fection, and both damp- and waterproof. A small fly which the ordinary observer dis misses as nothing but a gnat, makes it her busi ness to lay her eggs in the halictus's cells. Un der the microscope she is revealed as a red eyed, white-faced, gray-corseleted, black-legged marauder. One species of this family studied by Fabre, the zebra halictus, possesses a quality rarely ob served in the insect world-interest in grand children. The mother bee, of the spring gen eration, having passed the winter in some frost proof retreat, gives the mansion she has built so laboriously to her daughters. Each daugh ter builds a small addition to the burrow and makes a group of cells of her own, but all use the main burrow in common. The grandmother of the brood in the cells stands guard at the doorway, to.keep out all but the rightful entrants-her daughters. Her velvet dress, so clean and handsome when she was a youthful matron, is now threadbare and dingy. Gone is the nap, all but lost are the beautiful stripes of red and brown. But she has a grandmother's pride in the newly hatched grubs, and woe betide any crea ture who cannot show the yellow foot of the halictus folk when seeking to reach those grub chambers! A drubbing the marauder never will forget will be his certain portion. At the door, all day long, sits poor, bald-headed grand mother, a ghost of her former self, in a little sentry box at the mouth of the burrow, step ping aside to all those who can give the coun tersign, but wild as a witch in her anger to ward any would-be intruder. Mayhap her re markable guard over her grandchildren comes from the knowledge that some of them will be males. Denied the privilege of having sons, by that strange quirk of Nature which makes all the children of the spring generation fe males, she must look to her grandchildren for her male progeny. And each of those grand children is hatched into the world without a father. With no males produced from the eggs of the spring mother, and no males having survived the winter, they perforce are born under that strange departure from the orthodox laws of reproduction known as parthenogenesis.