8 NATURAL SCIENCE [July 
_A Srupy IN PARASITISM 
BuuuetIn No. 5 (Technical Series) of the same department con- 
tains an exhaustive account by Mr L. D. Howard of the insect- 
enemies of the white-marked tussock moth (Orgyia leucostigma), 
The hairy caterpillars of this moth have become, during recent 
years, highly injurious to foliage trees in the cities of the northern 
States. It appears that the vast multiplication of these caterpillars 
began with the introduction of the European sparrow. This bird 
has well-nigh exterminated other caterpillars which used to compete 
with the ‘ tussocks’ for a livelihood on the trees; it will not touch 
the hair-protected ‘tussocks’ itself, but it has largely driven out 
the native birds which used to feed on them. Fortunately, how- 
ever, an army of insect-parasites keep the caterpillars from increas- 
ing beyond all bounds. Fifteen species of Hymenoptera and six of 
Diptera are described as laying their eggs in either larva or pupa of 
the Orgyia. These parasites are in their turn subject to attack by 
thirteen species of minute Hymenoptera. An alarming increase of 
the ‘tussocks’ at Washington during the summer of 1895 was 
accompanied by a corresponding increase in the parasites, so that 
the vast majority of the caterpillars were destroyed. The next year, 
however, owing to the work of the secondary parasites, the ‘ tussock’ 
recovered its ground to a considerable extent. Two species of tiny 
hymenoptera were. proved to be ‘tertiary’ parasites, their grubs 
devouring those of the secondaries. Finally, eleven species of 
Diptera act as scavengers, their grubs feeding on the dead pupae and 
cocoon-masses of the contending insect-armies. 
A StupY IN COMMENSALISM 
Ir is cheering to turn from this summary of conflict and slaughter 
to another side of insect-life lately investigated by Mr C. Janet. 
In a little work of 62 pages (“ Sur le Lasius mixtus, Y Antennophorus 
uhlmanni, &c.”: Limoges, 1897) he describes the relations which 
subsist between social ants (Zasivs) and certain gamasid mites and 
other arthropods which are found in their nests. The mites of the 
species Antennophorus uhlmanni are carried about by the worker 
ants ; in their penultimate and adult stages they seem unable to 
make their own way about the nest, and wait feeling with their long 
front legs for an ant to which they can attach themselves. An ant 
normally carries three of the mites—one under the head and one on 
either side of the abdomen; these positions are the least incon- 
venient possible to the ant. The mites feed entirely on liquid dis- 
gorged by their hosts. An individual under an ant’s head naturally 
