Wasps are harmful or troublesome in three ways: (1) by gnawing the bark of trees; (2) by feeding on sweet fruits; (3) by the painful stings which they inflict. These are most dangerous in hot summer days. If a nest situated in the soil is destroyed during ploughing the alarmed insects attack both men and horses, cases being known where their stings have proved fatal. The pain is chiefly caused by the poison introduced into the wound. On this account if the sting remains sticking in the skin it must not be drawn out simply with the fingers, but carefully, by means of the nails, lest the poison-bag is pressed and thus still more poison brought into the wound. _Remedies_: Cooling substances, _e.g._ ground carrots, apples or pears, cabbage leaves, damp sand. Rubbing in ammonia. If there is acute inflammation, a compress with sugar of lead. Family: =Fossores= (_Digging Wasps_). Several species of this group resemble the wasps in their habits, as well as through their black and yellow-tinged abdomens; but they are always distinguished from these by their fore wings, which are not folded together in a state of rest, and by their eyes, which are not kidney shaped. The shanks and feet possess thorns serviceable for digging. The sting of the female has no barbs, so that it is not torn off and left behind in the wound. The digging wasps are not social. They are lively and active; in summer the female often flies busily about near the ground in order to find a place for bringing up her young. She digs a hole in the earth in which she lays an egg. Then she buries an insect to serve as food for the young when hatched. Lest the insect to be buried should decompose, while, on the other hand, a living animal would not allow itself to be buried, the wasp first brings the insect into a condition in which it cannot make any voluntary movements. For this purpose most species sting the captured prey several times in the body, and thus often injure the ventral ganglia (p. 84); by this treatment the insect is not killed, but reduced to a condition of apparent death. Most digging wasps are useful, since they chiefly bury destructive kinds of insects. The =Common Sand Wasp= (_Ammophila sabulosa_, Fig. 89), buries caterpillars; the =Path Wasp= (_Pompilius viaticus_), spiders; the =Weevil-killing Sand Wasp= (_Cerceris arenaria_) and the =Fly-killing Sand Wasp= (_Mellinus arvensis_) respectively bury weevils and flies. [Illustration: FIG. 89.—The Common Sand Wasp (_Ammophila sabulosa_); natural size. ] Family: =Formicidæ= (_Ants_).