Cuap, VII. AN INSECT PEST. 171 
comes forth only by day, relieving the mosquito at sunrise with the 
greatest punctuality, and occurs only near the muddy shores of the 
stream, not one ever being found in the shade of the forest. In places 
where it is abundant, it accompanies canoes in such dense swarms as 
to resemble thin clouds of smoke. It made its appearance in this way 
the first day after we crossed the river. Before I was aware of the 
presence of flies I felt a slight itching on my neck, wrist, and ankles, 
and on looking for the cause saw a number of tiny objects, having a 
disgusting resemblance to lice, adhering to the skin. This was my 
introduction to the much-talked-of Piim. On close examination they 
are seen to be minute two-winged insects, with dark-coloured body and 
pale legs and wings, the latter closed lengthwise over the back. They 
alight imperceptibly, and squatting close, fall at once to work, stretching 
forward their long front legs, which are in constant motion and seem to 
act as feelers, and then applying their short, broad snouts to the skin. 
Their abdomens soon become distended and red with blood, and then, 
their thirst satisfied, they slowly move off, sometimes so stupefied with 
their potations that they can scarcely fly. No pain is felt whilst they 
are at work, but they each leave a small circular raised spot on the skin 
and a disagreeable irritation. The latter may be avoided in great 
measure by pressing out the blood which remains in the spot; but this 
is a troublesome task, when one has several hundred punctures in the 
course of a day. I took the trouble to dissect specimens to ascertain 
the way in which the little pests operate. The mouth consists of a pair 
of thick fleshy lips, and two triangular horny lancets, answering to the 
upper lip and tongue of other insects. This is applied closely to the 
skin, a puncture is made with the lancets, and the blood then sucked 
through between these into the cesophagus, the circular spot which 
results coinciding with the shape of the lips. In the course of a few 
days the red spots dry up, and the skin in time becomes blackened 
with the endless number of discoloured punctures that are crowded 
together. The irritation they produce is more acutely felt by some 
persons than others. I once travelled with a middle-aged Portuguese, 
who was laid up for three weeks from the attacks of Pitim, his legs 
being swelled to an enormous size, and the punctures aggravated into 
spreading sores.* 
A brisk wind from the east sprang up early in the morning of the 
22nd ; we then hoisted all sail, and made for the mouth of the Rio Negro. 
This noble stream at its junction with the Amazons seems, from its 
position, to be a direct continuation of the main river, whilst the 
Solimoens, which joins at an angle, and is somewhat narrower than its 
tributary, appears to be a branch instead of the main trunk of the vast 
water-system. One sees therefore at once how the early explorers 
came to give a separate name to this upper part of the Amazons. The 
Brazilians have lately taken to applying the convenient term Alto 
Amazonas (High or Upper Amazons) to the Solimoens, and it is 
* The Piim belongs probably tc the same species as the Mosquito of the Orinoco, 
described by Humboldt, and which he referred to the genus Simulium, several kinds 
of which inhabit Europe. Our insect is nearly allied to Simulium, but differs from 
the genus in several points, chiefly in the nervures of the wings. 
