In the absence of man these mosquitos will suck blood from other animals, and in confinement they are generally fed on rats or canaries, and they will even suck up a drop of blood presented on a piece of cotton-wool.
If the female mosquito has been fertilised before the sucking of blood she will commence egg-laying two or three days later, and two or three days later again the larva will emerge. The larval stage lasts from nine to twelve days, and the pupa stage three to four, so that the whole metamorphosis takes from sixteen to twenty-two days. Hence, during warm weather, many generations succeed each other, but one must have a temperature of at least 20° to 27° C. Below that temperature the processes tend to slow down, and under a temperature near freezing-point the regular development is definitely interrupted. But the interruption is only a suspense, and living activities are resumed should the temperature rise again.
It is a disputed point whether these mosquitos must have a meal of blood before they can lay eggs, and on this point the evidence is not yet sufficient to make a dogmatic statement. These mosquitos are very indifferent where their eggs are laid. The smallest collection of water in an empty sardine-tin, a broken tumbler, a puddle in the street, a gutter-pipe, is good enough for Stegomyia calopus. She will even lay her eggs on moist cotton-wool.
Although Stegomyia bites freely during the day-time, it, as a rule, avoids the light and seeks some dark shelter. Contrary to the habits of Anopheles, it prefers a light ground to rest upon. The larvae live on algae, vegetable-matter, or plant-detritus, or, in captivity, on white bread or Indian corn. They can remain for a considerable time without food, and this without materially diminishing the rate of their development. Stegomyia breeds well in ships, and is occasionally found in one part only of the ship—such as the engine-room or cook’s galley, where the conditions seem to be most favourable to its development. Thus it comes about that at times certain quarters of a ship provide the greatest percentage of yellow-fever cases.
CHAPTER X
THE BISCUIT-‘WEEVIL’[12] (Anobium paniceum)
‘Let us be merry,’ said Mr. Pecksniff. Here he took a captain’s biscuit. ‘It is a poor heart that never rejoices; your hearts are not poor. No!’—(Dickens, Martin Chuzzlewit.)
The first things to notice about the biscuit-‘weevil,’ so familiar to readers of Marryat’s novels, is that it is not a weevil at all, and that it attacks a great many other comestibles besides biscuits. The so-called biscuit-‘weevil’ is in truth an Anobium—Anobium paniceum—a member of the family Ptinidae and is closely allied to A. striatum, which makes the little round holes in worm-eaten furniture, so cleverly imitated by the second-hand furniture-dealers. Another species of Anobium (recently re-christened Xestobium tessellatum), a somewhat larger insect, is destructive in churches, libraries, and old houses. Their mysterious tappings (which are really efforts to attract the other sex—mere flirtations) are the cause of much superstitious dread in the nervous, and this species is known as the ‘greater death-watch.’
Fig. 30.—Biscuit-‘weevil,’ Anobium paniceum. (From David Sharp, The Cambridge Natural History, vol. vi.)
But to return to the biscuit-‘weevil.’ The mature insect is about a quarter of an inch long, and lives at large; it is the larva which burrows into and attacks the dried biscuit—the ‘hard-tack’ of the Navy. Less of a woodborer than its allies, it nevertheless attacks almost any vegetable substance; and Butler tells us that ‘rhubarb-root, ginger, wafers, and even so unlikely a substance as Cayenne pepper have been greedily devoured by it.’ Several generations have been known to flourish on a diet of opium, and it has been found in tablets of compressed meat. Vegetable matter, even in an altered state—such as paper—affords it an ample meal; and in one case the larva of an Anobium paniceum bored steadily in a straight line through twenty-seven folio volumes in a public library, and so straight was the tunnel that a string could be passed through it from end to end. In one of our libraries at Cambridge some Arabic manuscripts were almost entirely destroyed by the larvae, which do not hesitate to browse on drawings and paintings and the dried paper of herbaria.