105 
but before these seeds ripened it was found that every head 
normally containing them had been eaten into and emptied of 
them. This good work was performed by the caterpillars of 
the above moth. They were so thoroughly well protected by 
their color and position that it was almost impossible to detect 
them, and only by beating the plants could they be obtained in 
large numbers. Those caterpillars that rested upon the 
greener portion of the plant possessed acorresponding green 
color, while those that rested upon the browner parts were 
brown. ‘They were also much more spotted and almost spiny, 
so that they blended well with the spiny appearance of this 
composite plant. Like the tassel-worm they entered the ground 
and appeared as moths between Oct. 10 and 15. The moth re- 
sembles that of the tassel-worm, but has darker markings. 
This species was also found flying during a bright sunny after- 
noon on June l. Since the disappearance of the rosin-weed the 
insect has not been found again. The moth is illustrated in 
Fig. 54, Plate 11 (the darker one). 
The above case is an instance where an injurious insect may 
become beneficial, and a number of other cases were discovered 
here, where otherwise injurious insects became our friends. 
The native cabbage-butterfly, which is decidedly a noxious -in- 
sect, utilized the Russian thistle as a food plant, and immense 
numbers of their caterpillars could be found upon this danger- 
ous weed. 
An european weed, which has recently found its way to our 
state, the stork-bill (Hrodium cicutarvum 8S. Her.), has been 
almost entirely killed off by the caterpillar of a nocturnal in- 
sect (Pyrrhia angulata Grt.) which is, however, the european 
Pyrrhia umbra of Hbn. 
Our common bull-thistle, which at one time almost entirely 
covered some waste places near the farm, has almost disap- 
peared. This was owing to the good work of asmall moth be- 
longing to the family of Pterophoride. Many other cases 
could be given, where noxious insects have done good by eat- 
ing weeds. 
