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Golden-eyed Lace-winged Flies — Part 1

(Family Chrysopidae.)

These little insects are known as the golden-eyed lace-winged flies. They are generally green in color, and their eyes, while appearing brown in some lights, have a distinct yellowish, almost phosphorescent or metallic glint in other lights, which accounts for the name golden-eyed. They are sometimes appropriately called stink flies. The uncautious observer, attracted by their beauty, on handling them is at once conscious of a disagreeable and very strong odor which is with difficulty removed from the fingers by soap and water.

The eggs of these little flies are very curious. Each is placed at the extremity of a long slender stalk, which is a most necessary method of egg-placing, on account of the voracity and omnivorous habits of the newly hatched larvae. If they were laid on the surface of a leaf side by side, as is the case with so many other insects, the first larva which hatched would eat up all of the other eggs, but, issuing as it does from the egg on the top of this long inedible stalk, finding himself on the leaf there is nothing for him to eat unless he searches for plant-lice, of which there is generally an abundance nearby. The eggs are usually deposited on leaves or twigs, and, with wise foresight, customarily in the middle of a colony of plant-lice, and the young larvae after hatching begin immediately to feed upon the nearest prey. They are most voracious, and insert their long, pointed, sickle-shaped jaws (like those of the Hemerobiids) into the body of the nearest soft-bodied insect. It should be stated first, however, that on hatching, the upper end of the egg is cut off by the larval jaws.

The young larva has an extremely large head, and the sides of its body are armed with immense curved hairs, which give it a very ferocious appearance. It crawls down the egg stalk until it reaches the object upon which it is placed. On reaching a young plant-louse it grasps it between its long curved jaws and rolls it one way or the other, the juicy contents being rapidly extracted. It seems always hungry and always to be feeding when it can find anything upon which to feed, and its rapidity of growth is limited only by the abundance of the food supply. It will eat one of its own brothers as quickly as any other insect, and when nearly full grown its jaws are strong enough to pierce the skin of a human being. In Toronto, Canada, I once felt a sharp prick on the knuckle of one of my fingers, and on looking down found one of these larvae with both jaws sticking through the skin and pumping away with its body in an effort to get some nourishment. I watched it for some time under a lens with some interest, and am glad to state that it did not seem satisfied with its meal.

The insect transforms to pupa within the interior of a white spherical, silken cocoon, which is very characteristic in appearance, and the adult escapes through a circular hole to which the cap remains attached like a lid.

The golden-eyed lace-winged flies are among the most important enemies of the injurious plant-lice which swarm upon many valuable plants especially in the early part of the summer. The mother fly lays her eggs where possible in the midst of colonies of plant-lice, and these are rapidly swept out of existence after the eggs are hatched.

A few of these lace-winged fly larvae have the same habit which we have described as occurring with the Hemerobiids, of covering themselves with the skins of their victims. Hubbard has studied a species which feeds upon bark-lice, tearing the scales loose from the bark and devouring the soft contents, and then adding a portion of the debris to the load on its back.

Unfortunately, these beneficial lace-winged flies are subject to the attacks of certain parasitic chalcis flies which sting their cocoons. The species of the interesting genus Isodromus seem to confine their attacks exclusively to the cocoons of lace-winged flies.

Life History of a Golden-Eye

(Chrysopa oculata Say.)

This is one of the commonest species in this group, and is often mentioned in books on economic entomology as destroying plant-lice and other injurious insects. The only observer to describe its life history with any detail, however, is Marlatt, from whose observations the following statements are drawn.