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BEETLES – The popular name for members of the order Coleoptra – the largest of all the insect groups. (Two out of every 5 insects discovered and named are beetles.) They usually have hardened outer skins or shells. The front pair of wings is veinless and thickened, forming two convex shields (called elytra) which, when the insect is at rest, meet in a straight line down the back, covering the folded, membranous, veined, hind wings, with which the creature flies. In flight, the elytra stand out stiffly sidewise like the wings of a monoplane. The mouth parts are of the typical chewing type, except in one group, the snout beetles, in which they are greatly reduced in size and placed at the end of a slender trunk-like snout.

Beetles, in growing, go through a “complete metamorphosis”. The larvae are worm-like grubs, usually with six true legs (like the adult), though the snout beetle maggot is legless. The head of the grub is always distinct from the body and is usually dark in color. The pupa or resting stage is a brown shiny oval object with a slight but peculiar squirming or wiggling ability. These pupae are not enclosed in dense silky cocoons like those of most butterflies and moths, but may be found unprotected in the soil or in burrows in infested trees or plants.

Since both larvae and adults have chewing mouth-parts, beetles are commonly injurious in both stages, but in a few cases one stage is injurious while the other is beneficial. Adult blister beetles, for instance, feed on foliage and flowers but the grubs are helpful because they eat the grasshopper eggs in the soil. Lady beetles and ground beetles (which see) are highly beneficial since, both are larvae and as adults, they devour other insects that are injurious to the garden.

Since beetles are chewing insects the general recommendation for control is the use of a stomach poison, such as arsenate of lead, calcium, or magnesium. There are, however, many cases when this rule should not be followed. Foliage can usually be protected with lead arsenate, but spraying flowers with this material is often undesirable or inadvisable. Hence flower-loving beetles, such as the Japanese beetle, the blister beetle and the rose chafer, are best destroyed by hand picking, or by knocking them off into a pail of water with a layer of kerosene on top.

Grubs of the Japanese and Asiatic beetles, as well as white-grubs (which see), can be poisoned by applying lead arsenate to the soil or killed by injecting carbon bisulphide into it. The elm leaf beetle is readily kept from defoliating trees by spraying them with a stomach poison, but beans in the vegetable garden cannot be protected from the Mexican bean beetle in this way except while the plants are small because of the danger of arsenical residue on the beans. In this case contact insecticides are resorted to for the later sprayings.

Small active beetles such as flea beetles are often warded off by a repellent such as bordeaux mixture or may be sprayed with a contact insecticide. Bark beetles or borers can be destroyed only by mechanical means or by fumigation.