[Illustration: FIG. 88--Top-minnow (_Mollienisia latipinna_). (From Bull., 47 U.S. Fish Com.)] [Illustration: FIG. 89--Dragon-flies. (From Kellogg's Amer. Insects.)] On account of the various habits of both the larvæ and adults it will never be possible for any natural enemy or group of natural enemies effectively to control the mosquitoes of any region, but as certain of them are important as helpers they deserve to be mentioned. ENEMIES OF THE ADULTS Birds devour a few mosquitoes, the night-flying forms being particularly serviceable, but the number thus destroyed is probably so small as to be of little practical importance. The dragon-flies (Figs. 89, 90, 91) or mosquito hawks have long been known as great enemies of mosquitoes, and they certainly do destroy many of them as they are hawking about places where mosquitoes abound. Dr. J.B. Smith of New Jersey very much doubts their efficiency, but observations made by other scientific men would seem to indicate that they often devour large numbers of mosquitoes during the course of the day and evening. Spiders and toads destroy a few mosquitoes each night. Certain external and internal parasites destroy a few more, but the sum total of all of these agencies is probably not very considerable, for while the adults may have several natural enemies they are not of sufficient importance to have any appreciable effect on the number of mosquitoes in a badly infested region. ENEMIES OF THE LARVÆ AND PUPÆ The larvæ and pupæ on the other hand have many important enemies. Indeed under favorable conditions these may keep small ponds or lakes quite free from the pests. The predaceous aquatic larvæ of many insects feed freely on wrigglers. The larvæ of the diving beetles which are known as water-tigers are particularly ferocious and will soon destroy all the wrigglers in ponds where they are present (Fig. 92). Dragon-fly larvæ also feed freely on mosquito larvæ. Whirligig beetles are said to be particularly destructive to _Anopheles_ larvæ and many other insects such as water-boatmen, back-swimmers, etc., feed on the larvæ of various species. A few of these introduced into a breeding-jar with _Anopheles_ larvæ will soon destroy all of them, even the very young bugs attacking larvæ much larger than themselves. It is interesting to note that the larvæ of some mosquitoes are themselves predaceous and feed freely on the other wrigglers that may chance to be in the same locality. [Illustration: FIG. 90--The young (nymph) of a dragon-fly. (From Kellogg's Amer. Insects.)] [Illustration: FIG. 91--The cast skin (exuvæ) of a dragon-fly nymph.] [Illustration: FIG. 92--Diving-beetles and back-swimmers. (From Kellogg's Amer. Insects.)]