FOSSOKIAL HYMENOPTEEA 
449 
still — namely, the case of the Mutillidce, which, as has been 
said, lay their eggs in the nests of other Hymenoptera, including 
Eossors ; and, lastly, several Fossors have become thieves, and, 
instead of hunting for themselves, dart down at a favourable 
moment and lay their eggs on the prey which a more honest 
relative is about to store up for her own. The pirate larva 
develops more quickly, and hence the food is eaten before 
the rightful owner is full grown ; hence it dies of starvation. 
Thus the pirate may, by destroying the destroyer of a harmful 
insect, range itself against man. And so the balance of nature 
swings, up and down, and man can only look on and marvel 
at the intricacy of it. 
Having now broached the subject of the natural enemies 
of Fossors, I propose to make a diversion and discuss that 
point and its relation to the colours of these insects. The 
absorbing study of the colouration of insects has only been 
made intelligible by the Darwin- Wallace hypothesis of Natural 
Selection. 
On this hypothesis, certain insects are rendered relatively 
inedible to mammals and birds by the possession of a dis- 
agreeable taste, a sting, extreme hardness, spines or hairs, &c. 
I may say, in passing, that this has now been abundantly 
proved by experiment with insectivorous animals and birds. 
It has been to the advantage of such insects that these qualities 
should be made known as efficiently as possible ; for a mere 
experimental peck or bite or taste by an inquisitive enemy 
may destroy an insect as much as eating it, or at least render 
it incapable of reproducing its kind. 
Hence natural selection has brought it about that such 
‘ protected ’ insects have conspicuous, easily recognised, 
gaudy colours in simple patterns — such as the alternating rings 
of yellow and black exhibited by many stinging Hymenojptera, 
or the bright red and black of many Acrcea butterflies. An 
insectivorous bird or animal, having in its youth learnt the 
disagreeable taste of such brightly coloured insects, for the 
future disregards them in favour of more edible food, so long 
as this is to be had, knowing that a conspicuously coloured 
insect is likely to be offensive. Hence such colours are known 
as ‘ aposematic ’ — a term which literally means ‘ warning oft’.’ 
