534 Dn Dipt era as Spreaders of Disease, [September, 
intrude into our dwellings, hover around us in our walks, 
and harass us with noise and constant attempts to bite, or 
at least to crawl upon us. Even the ants, except in a few 
tropical districts, rarely a Ct upon the offensive. The He- 
miptera contain one semi-parasitic species which has attained 
a “world-wide circulation,” and one degraded, purely para- 
sitic group. But the Diptera, among which the fleas are 
now generally included as a degenerated type, comprise more 
forms personally annoying to man than all the remaining 
insert orders put together. These hostile species are, fur- 
ther, incalculably numerous, and occur in every part of the 
globe. Mosquitoes swarm not merely in the swampy forests 
of the Orinoco or the Irrawaddy, but in the Tundras of 
Siberia, on the storm-beaten rocks of the Loffodens, and are 
even encountered by voyagers in quest of the North Pole. 
The common house-fly was probably at one time peculiar to 
the Eastern Continent, but it followed the footsteps of the 
Pilgrim Fathers, and is now as great a nuisance in the 
United States and the Dominion as in any part of Europe. 
It is curious, but distressing, to note the tendency of evils to 
become international. We have communicated to America 
the house-fly and the Hessian fly, the “ cabbage-white,” the 
small-pox, and the cholera. She, in return, has given us the 
Phylloxera, a few visitations of yellow fever, the Blatta gi - 
gantea, and, climate allowing, may perhaps throw in the 
Colorado beetle as a make-weight. In this department, at 
least, free trade reigns undisputed. It is a singular thing 
that no beautiful, useful, or even harmless species of bird or 
inseCt seems capable of acclimatising itself as do those cha- 
racterised by ugliness and noisomeness. 
But, returning from this digression, we find in the Diptera 
the habit of obtrusion and intrusion, of coming in aCtual 
contadt with our food and our persons, combined with 
another propensity — that of feeding upon carrion, excrement, 
blood, pus, and morbid matter of all kinds. This is a com- 
bination far more serious than is generally imagined. If the 
fly — which may at any moment settle upon our lips, our eyes, 
or upon an abraded part of our skin — were cleanly in its 
habits, we need feel little annoyance at its visits. Or if it 
were the most eager carrion devourer, but did not, after 
having dined, think it necessary to seek our company, we 
might hold it, as is done too hastily by some naturalists, a 
valuable scavenger. I fear, however, that I have already 
made too great a concession. So long as very many persons 
are suffering from disease, — so long as many diseases are 
capable of being transmitted from the sick to the healthy,— 
