. The Cambridge natural history. Zoology. 26 HYMENOPTERA CHAP. in colonies. Great difficulties attend their study on account of several points in their economy, such as, that the sexes are different, and frequently not found together; also that there may be two generations of a species in one year, these being more or less different from one another. Another considerable difficulty arises from the fact that these bees are subject to the attacks of the parasite Sti/lops, by which their form is more or less altered. 1 i/ -L ' v These Insects feed in the body of the bee in such a way as to affect
. The Cambridge natural history. Zoology. 26 HYMENOPTERA CHAP. in colonies. Great difficulties attend their study on account of several points in their economy, such as, that the sexes are different, and frequently not found together; also that there may be two generations of a species in one year, these being more or less different from one another. Another considerable difficulty arises from the fact that these bees are subject to the attacks of the parasite Sti/lops, by which their form is more or less altered. 1 i/ -L ' v These Insects feed in the body of the bee in such a way as to affect its nutrition without destroying its life ; hence they offer a means of making experiments that may throw valuable light on obscure physiological questions. Among the effects they produce in the condition of the imago bee we may mention the enfeeble- ment of the sexual distinction, so that a stylopised male bee becomes less different than it usually is from the female, and a stylopised female may be ill developed and less different than usual from the male. The colours and hair are sometimes altered, and distortion of portions of the abdominal region of the bee are very common. Further particulars as to these parasites will be found at the end of our account of Coleoptera (p. 298). We may here remark that these Stylops are not the only parasitic Insects that live in the bodies of Andrenidae without killing their hosts, or even interrupting their metamorphoses. Mr. E. C. L. Perkins recently captured a specimen of Halictus rul)icundus,fcom which he, judging from the appearance of the example, anticipated that a Stylops would emerge ; but instead of this a Dipterous Insect of the family Chloropidae appeared. Dufour in 1837 called attention to a remarkable relation existing between Andrena aterrimaand a parasitic Dipterous larva. The larva takes up a position in the interior of the bee's body so as to be partly included in one of the great tracheal FIG. 13.—Parasitic Dipterous v
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