144 GNATS OR MOSQUITOES — CHAPTER VII be will find it difficult to find them away from the neighbourhood of habitations.
These larvae may almost be said to be in a sort of resting condition, or in other words, they are not growing, and, as a rule, no pupae will be found, though the occurrence of a day or two of warmer weather, will lead to their appearance, especially in the case of the Culices. Towards the middle of February, these two hardy species commence to renew breeding operations in a leisurable way, but as far as I can make out, it is only C. fatigans that dares to brave the fierce heat of the dry season, C. impellens retiring into obscurity in March, until the advent of the rain makes climatic conditions more tolerable, alike for Mosquitoes and men. At the end of March, C. fatigans was absolutely the only species I could find, but it made up for the want of its kindred by its enormous numbers, as the small, constantly replenished tanks in the gardens, which afforded the only possible nurseries for Mosquitoes of any sort, were well-nigh solid with their larvae and pupae, and they so swarmed in the bungalows, as to make the evening and night intolerable. In the open, or anywhere away from houses, it is needless to remark that no Mosquitoes of any kind were to be found, and they continued to be the only species present in at all noticeable numbers, until the break of the rains, in the end of June, or beginning of July. In the middle of April, however, the Anopheles larvae that have tided through the winter, pupate, and give birth to a spring brood of adults, but as the climatic conditions are unfavourable at this time to its breeding operations, on account, I fancy, of the available collections of water being too hot for the taste of the larvae ; which will swarm in the very same situations a couple of months later, and hence no fresh broods appear, and the imagines that made a short appearance on the scene hide themselves for the rest of the dry season : as none of my correspondents make any mention of having met with them in our part of the country at this time of the year. With the advent of the rains, however, a renewed period of activity commences. Anopheles larvae make their appearance in
LIFE HISTORY AND SEASONAL PREVALENCE 145 every available pool, and soon strange Culiciform larvae, with short breathing tubes will be found in the pools of fairly clean rain water that form in every depression of the ground. Before long G. fa tig a ns, though still taking a considerable share in the business of rendering human existence less endurable, is thrown into the shade by numbers of small Mosquitoes " brindled " with intensely contrasted black and white, while the unobtrusive Anopheles, though really present in large numbers are less importunate in their attentions, and will not so readily be found by the unpractised searcher. On this account, and because they are more purely nocturnal than the Ciilices, those who do not know where and when to look for them may be led to report them as scarce or absent, though in reality they may be present in large numbers. I suspect too that the elevation of an upper storey affords a more secure haven from their attacks than is the case with Culex. Mr. Aitken, in the paper already quoted, remarks : — "As regards the mature Anopheles, the most remarka,ble fact in my notes is that I have not seen one during these last twelve months, excepting those that I reared. This fact will give the best idea of what an insidious ■enemy we have to deal with. I lived most of the year at the Bombay Club, within a stone's throw of the Frere Fountain, in which Anopheles was being produced by the thousand, but I never saw one, though I was often tormented by Culex, the larvae of which were comparatively scarce. Anopheles is a small, sHm Mosquito, of a pale, ashy-grey colour, difficult to see at any time, and it appears to fly only by night, so it is rarely seen. Add to this that its bite appears to be almost painless, and you will see that one may have malaria injected into him night after night while he is sleeping without curtains, under the belief that there are no Mosquitoes. I say that its bite is almost painless on the authority of my own experiments only. I kept mine in a bottle with thin muslin tied over the mouth, and if I laid my arm on the muslin the females attacked me at once and did not leave off till they were bloated with blood. I sometimes felt a slight prick at the moment when they 10
146 GNATS OR MOSQUITOES — CHAPTER VII punctured the skin, but there was Httle or no irritation afterwards and no swelhng. Of course, others might have been affected differently. The males never attempted to suck my blood, but they fed freely, as did the females also, on a slice of apple, fig, mango, or any juicy fruit. In default of fruit I gave them jam, or even sugar and water. After a meal of blood they seemed to feel heavy and indisposed for active exercise, but were quite ready again in twentyfour hours. It has been stated that Anopheles is mute. This is certainly a mistake. It has a very shrill pipe." The brindled Mosquitoes above alluded to are Stegomijice, but, in addition to these, Tmiiorhynchus ager, Mihi, Mucidus scatapliagoides, Mihi, and a number of Culices, such as C. concolor, E. Desv., which are entirely absent to all appearance at other times of the year, may be found in greater or less numbers. In October, I took at Shahjahanpur, a solitary specimen of C. mimeticus, Noe, but I suspect that this is rarely found during the rains in the plains, as it was not included in any of the collections sent me for identification from this part of India. I also took at this period, the single specimen from which Corethra Asiatica, sp. n. is described, but this species is so small and inconspicuous that it is easily overlooked, and it is probable that the example I captured was a late specimen of a species that may be common enough during the rainy season. With the drying up of the rains, these species, peculiar to that season of the year, cease to be seen, and retire into a seclusion that cannot fall far short of seven or eight months; but the Anopheletes linger longer, and may be found, though in rapidly diminishing numbers, till late in November. Towards the end of the period An. sinensis, previously the less common, is far more often met with than An. Bossii, but the very last specimen I was able to find during the year was one of the latter species (on November 22nd). In a note dated two days previously, I find that a male sinensis was so sluggish m the early morning (temperature 56' F.) that he refused to fly, though he revived somewhat during the day, when taken into the sunny verandah to pose for his photograph. After this.
LIFE HISTORY AND SEASONAL PREVALENCE 147 no others than the two species mentioned as still present in January could be found, and it is again not until April that any were observed by my friend, Mr. Royle, who then found them again in evidence in Shahjahanpur. Such is roughly the seasonal prevalence of the family in the Province to which my own observations have been almost confined, but those who are not familiar with the wide range of chmatic conditions found within the peninsula must not be misled into supposing that the account can be accepted for the entire country, or that it is even typical of any large proportion of its area. In illustration of this, I quote a further extract from Mr. Aitken's paper and a few of the replies published in the Indian Medical Gazette, in response to a circular of queries issued by Major Buchanan, I.M.S., the editor of that journal. Mr. Aitken says : " In the first place, you will note that I have found Anopheles larvae in every month of the year, except February, when I did not look for them. But I had plenty in captivity during that month, which I had brought home in January. So it appears that, in a place with a moist climate, in which there is always some water to be found, Mosquitoes can survive without hybernation and may be found at all seasons. But as with other insects generally in this Presidency, the time when they are most abundant is the close of the rains."
Captain Giffard, I.M.S., notes that on the Coromandel coast the malaria-bearing Mosquitoes were extraordinarily prevalent, even at the end of the cold season, and existed in thousands in every pool, well, and casuarina pool examined.
Captain Cornwall, I.M.S., states that in Madras, Mosquitoes are never entirely absent, but they are most common, when a sufficiency of water is lying about, i.e., in January, February and March, after the rains. They decrease in the hot weather and increase again in the showery months of July, August and September. In the last three months of the year, when the heavy rains have swamped the breeding places, the Mosquitoes, both adult and larval, are most difficult to find.
148 GNATS OR MOSQUITOES— CHAPTER VII Captain C. J. Fearnside, I.M.S., writes that in Rajalimundri, Mosquitoes seem to exist all the year round, and that he finds that Anopheles breeds anywhere, in a beaker of water as well as in a puddle. He has also seen Anopheles feed greedily in the daytime. With regard to the evolution of the malarial parasite, Captain Fearnside notes that in some species of Anopheles crescents and spring tertian parasites will not develop at all, the crescents may be " old and impotent " (Grassi), but this will not explain the nondevelopment of the spring tertians. He also noted that he had frequently found crescents in cases known to have suffered from only mild attacks of fever.
Major J, Smyth, I. M.S., writes from Bangalore that Mosquitoes are present throughout the year, but in diminished numbers in January and December. Last year Anopheles were present in certain localities in large numbers, especially in July. The following note is of special interest : last year at Bangalore some new plots of land were opened out for the extension of the town, and one of the new extensions became so malarious that it had to be abandoned, all the children suffered from ague, and most of them developed enlarged spleens. In this part of the extensions Major Smyth found Anopheles larvae very prevalent in some low-lying pools ; in two other extensions no malaria prevailed and no Anopheles larvae could be found. This observation at Bangalore is very interesting in connection with the much discussed question of malarial outbreaks among men employed in engineering and building operations.
From Berhampur, Bengal, Major J. H. T. Walsh, I. M.S., writes that Anopheles is present in small numbers all the year, but only a few in the dry hot months. They appear in large numbers during breaks in the rains, and after the heavy floods of last September none were seen for several days. Though Berhampur is a very " malarious " district, very few cases of true "ague" were seen in the jail and asylum. Anopheles larvae seem to breed everywhere he says, in tanks, or even in a bathroom. Major C. R. M. Green, I.M.S., F.KC.S., writes from
LIFE HISTORY AND SEASONAL PEEVALENCE 149 Mozufferpore that Mosquitoes are present all the year, but most common in September, October and November. The adult Anopheles is most easily found in October and November.
Captain Maddox writes from Chapra that August, September and October are the worst months for Mosquitoes. He has found Ajiopheles larvae in small pools and ditches near habitations.
Writing from Benguela, in Portuguese West Africa, Dr. A. Yale Massey says that the hot, wet season lasts from October to April, and that Mosquitoes appear in November. There is comparatively little fever before December, and cases occur as late as June, but January and February are the worst months.
Speaking generally then, it may be safely asserted that, for any given locality, the seasonal prevalence of Mosquitoes may be accurately predicated from an inspection of its tables of rainfall and temperature ; and that, provided Anopheletes be included in its fauna, malaria will make its appearance, in all warm climates, within a few weeks of the breaking of the rains.
It only remains to add a few words on the natural enemies of Mosquitoes in their various stages. Unfortunately, as Celli remarks, these are not numerous, and are rarely sufficiently numerous to perceptibly diminish the numbers of so prolific a family of insects. In the adult stage, birds, reptiles, frogs and certain insects devour them whenever they have the chance, and are not tempted by the superior attractions of larger game. The bright little gecko lizard, which is so commonly found in our Indian bungalows, should be always treated as an honoured guest for his services in this direction, especially as he does not strike work and go to sleep just when he is most wanted, as most birds do. Each of these quaint, half-tame little beasts may be looked upon as at least equal, in Mosquito-destroying efficiency to a fly-paper of the largest size, and their company should be encouraged accordingly. In the larval stage there can be no doubt of the efficiency of certain species of fish, and the apparent contradictions that appear
150 GNATS OR MOSQUITOES — CHAPTER VII in the communications one reads from various parts are simply due to the fact that the tastes of different species of fish as to their food differ Hke those of other orders of animals. That fish and Mosquitoes are constantly found in company in the Madras rice swamps simply shows that the species found there do not happen to be larvivorous, and in no way discredits the accuracy of other observers, who find that gnat larvae are unable to exist in water that contains fish of probably entirely different sorts. Per- .sonuUy I have never found fish in the same pool with larvae Fig. 32. —Caudal extremity of Anopheles Rosii infested by a parasitic stalked infusorian.
though, like Mr. Aitken, I find that they and tadpoles, and I may add frogs, seem to be able to live together as excellent friends. Mr. Aitken says : " From my experience I should say that, of all larvicides, the most effectual, in the case of Anopheles, is little fishes. I have never found larvae and fishes in the same pool. Once I put a large number of larvae into two glass vessels and introduced a few gold fish into each. Next morning there was not one larva in either. They have many insect enemies; too, especially
LIFE HISTORY AND SEASONAL PREVALENCE 151 the larvae of dragonflies, but one fish will do more than a hundred of these. Tadpoles do not eat them." On the other hand, there is a general concensus of evidence that the larvae of dragonflies are most efficient in this respect, and I believe that their universal presence in all collections of v^^ater of any size in upper India is the explanation of the fact that we so rarely find gnat larvae in such situations. The only parasite I have ever met with infesting the larvae is the small stalked infusorian represented in the accompanying illustration. I have repeatedly found every larva in a pool simply covered by these parasites, which lie crowded together in enormous numbers, attaching themselves especially to the softer parts of the integments, such as the angles between the anal tubercles, and the soft membranes between the segments. Larvae affected in this way have a peculiar, slimy appearance, and seldom appear healthy, though it is difficult to see how these ecto-parasites can be harmful, unless it may be that being, at the ver}^ least, greedy mess-mates, they may appropriate to themselves an undue share of the food that would otherwise fall to the share of their hosts. Nevertheless, I strongly suspect that they may be the cause of the inexplicable disappearance of larvae, already alluded to, from situations where they were just before present in abundance.
Since the above went to press, I have received from Dr. J. Cropper, of Chepstow, a slide containing some immature Acari which he found upon An. maculipennis, in Palestine. They are of cordate outline, nearly as wide as they are long, and are provided with a formidable suctorial mouth. From their comparatively large size, they must be formidable parasites to so small an insect, but only three specimens were observed to be infested in this way. They much resemble the hexapod larvae of certain bird-ticks.