_Andrena_ found in the pollen the egg of a parasitic _Nomada_, it could of course easily remove the egg; but the _Andrena_ has no conception that the presence of the egg ensures the death of its own offspring and though the egg be that of an enemy to its race, why should it resent the fact? Is it not clear that the race has always maintained itself notwithstanding the enemy? Nature has brought about that both host and parasite should successfully co-exist; and each individual of each species lives, not for itself, but for the continuance of the species; that continuance is provided for by the relative fecundities of host and guest. Why then should the _Andrena_ feel alarm? If the species of _Nomada_ attack the species of _Andrena_ too much it brings about the destruction of its own species more certainly than that of the _Andrena_. [Illustration: Fig. 16.—_Melecta luctuosa_ ♀. Britain.] Such extremely friendly relations do not, however, exist between all the parasitic bees and their hosts. Friese says that, so far as he has been able to observe, the relations between the two are not in general friendly. He states that marauders of the genera _Melecta_ and _Coelioxys_ seek to get out of the way when they see the pollen-laden host coming home. But he does not appear to have noted any other evidence of mistrust between the two, and it is somewhat doubtful whether this act can properly be interpreted as indicating fear, for bees, as well as other animals, when engaged in work find it annoying to be interfered {32}with; it is the interest of the parasite to avoid annoyance and to be well-mannered in its approaches. Shuckard, however, says that battles ensue between the parasite _Melecta_ and its host _Anthophora_, when the two bees meet in the burrows of the _Anthophora_.[26]