Knowledge. 



With which is incorporated Hardwicke's Science Gossip, and the Illustrated Scientific News. 



A Monthly Record of Science. 



Conducted by Wilfred Mark Webb, F.L.S., and E. S. Grew, M.A. 



MAY, 1913. 



THE RED-TAILED HUMBLE BEE. 



A STUDY IN MIMICRY. 



By G. W. BULMAN, M.A., B.Sc. 



Among our seventeen native species there is none 

 more easily recognised than the Red-Tailed Humble 

 Bee, the Bombits lapidarius of science. Its large 

 size, black body and red tail, are sufficient to enable 

 even those who take little notice of such things to 

 know it when they meet it in the fields. Even in 

 Shakespeare's time it would appear to have been 

 differentiated from the other species. For when 

 Bottom, in " A Midsummer Night's Dream," wished 

 for a sip of honey, his command to Cobweb was, 

 " Kill me a red-hipped humble bee on the top of 

 a thistle." 



And yet there is another bee so like it that it 

 requires some practice in diagnosis to detect the 

 difference. It is of the same size, and has also a 

 black body with a red tail. Yet there are points of 

 difference which enable the expert to detect the 

 mimic at once. It does not, far example, go busily 

 from flower to flower gathering honey to take home 

 to the nest. It only wants an occasional sip for its 

 own sustenance, and its idleness is quite apparent. 

 The wings are darker than in the Bombus, there are 

 no little baskets on the hind legs for collecting pollen, 

 and there is a curious shining, almost bald patch on 

 the upper surface of the abdomen. Had Monsieur 

 Cobweb killed it in mistake for the red-hipped humble 

 bee, he would have found no bag of honey. This bee 

 belongs to a group very near the true humble bees, 

 and sometimes known as parasitic humble bees. 



different group and 

 Noting the striking 



They have been placed in a 

 named Apathus, or Psithyrus. 

 resemblance we say, in the language of modern 

 zoology, here is a remarkable case of mimicry. And 

 when we learn that the mimic is a parasite on the 

 red-tailed humble bee, then, if we are believers in 

 the theory, we sav, " This resemblance enables the 

 parasite to enter the nest of the host more readily. 

 It has been acquired because those which possessed 

 it in the highest degree succeeded best in deceiving 

 the host, and so getting their young reared at its 

 expense." Shuckard, in his work on " British Bees," 

 writes of these parasites thus : — 



" Both sexes appear to have free in- and egress to, 

 the nests of those Bombi which they infest, without 

 any let or hindrance on the part of the latter, with 

 whom they seem to dwell in perfect amity." 



The resemblance of the parasite in the case of the 

 Red-tailed Humble Bee is certainly _ striking, and 

 according to the above, perfectly succeeds in its 

 purpose of deception. Yet one asks, Why should 

 such a perfect resemblance fail in more than one 

 important point ? Why should this bald patch, and 

 these dusky wings, betray it even to a somewhat 

 casual observer ? A little difference in the way of 

 greater hairiness, or lighter colour in the wings, 

 would have been so easy, and likely to occur as 

 chance variations ! And then it has, as Mr. Sladen 

 says, "a distinctly lower-pitched and softer hum." 



161 



