1924 ] 
Biological Notes on Lethocerus americanus 
179 
20 mm.; width of abdomen across base of second segment, a 
fraction more than 20 mm. 
That this nymph was of the last instar there can be no doubt 
as it was practically as large as some of the smaller adult Letho- 
cerus in my collection. A comparison of the size and shape of 
the wing pads with those of a fifth instar Belostoma flumineuin 
Say strengthens the opinion that such is the case. In the fol- 
lowing discussion the next to the. last and the last nymphal 
stages will be referred to as the fourth and fifth respectively, but 
for reasons to be giVen below, this may not be the proper desig- 
nation. 
The shape of the fourth and fifth instar nymphs is noticeably 
different. The widest measurement of the thorax in the fourth 
stage is the width through the hind ahgles of the metanotum 
(tips of rudimentary wing pads)^ which flare out slightly, while 
the greatest thoracic width of the fifth stage nymph is across the 
mesothoracic wing pads at a distance of about three millimeters 
before their tips. In the fourth stage the greatest abdominal 
width is two millimeters more than the greatest thoracic width. 
The mesothoracic wing pads lack about 1 mm. extending to the 
hind angles of the metanotum. These angles are not yet dif- 
ferentiated into wing pads. In the fifth instar nymph the greatest 
abdominal width is equal to the width across the tips of the meso- 
thoracic wing pads, which now extend slightly beyond the hind 
angles of the metanotum. In this stage the hind angles of the 
metanotum are clearly differentiated into wing pads. The 
greatest width of the bug is now across the thorax instead of 
the abdomen. Our attention has been called to the disappearance 
of one of the anterior tarsal claws during the last molt. Another 
difference between nymph and adult is that the nymph has a 
dense growth of hair on the ventral side of the abdomen, while 
the same region in the adult is glabrous and devoid of hair. 
Weed (1897) figures the ^'Last stage of nymph.’’ This 
undoubtedly is a drawing of a fourth stage nymph. It does not 
agree with the specimen before the writer, in that the shape of 
the wing pads is different. However, it could not possibly be a 
last nymphal stage. 
Since Belostoma has five nymphal stages it would be ex- 
