FERTILIZATION OF SPRING FLOWERS ON THE YORKSHIRE COAST. 95 



Throughout this paper I shall arrange the groups and the 

 species wilhiu the groups in a sequence which is more or less in 

 accordance with their efficiency. Firstly, in the Hymenoptera : — 

 the humhle-hees, with their regular liabits and long tongues 

 (Bombus hortorum, ^ 14-lG, ? 19-21 mm. ; B. agrorum, ^ 12-13, 

 ? 13-15 ; B. lapidarius, ^ 10-12, 2 12-14 ; and B. terrestris, 

 ^ 8-9, 2 9-11), and also the hive-bee (Apis melHfica, ^ 6 mm.), 

 are the best of Hower-fertilizers; next come tlie diligent Andrenidae 

 with tongues of mid-length, and less efficient, because they visit 

 only to feed themselves, and not to feed their young, the cuckoo- 

 bees, c.(j. Nomada; the short-tongued wasp, in spite of its diHgence, 

 is of considerably less use to plants ; and the lounging Ichneumons* 

 and creeping ants of scarcely any use. The second group of insects, 

 the Lepidoptera — often extremely long-tongued, but inconstant in 

 their attentions — are of considerable service to plants, though scarcely 

 to the spring flora. Proceeding to the flies, we have among them the 

 hover-tiies or Syrphidae, which in length of tongue and suitability 

 for flower-fertiUzation rank next to the Andrenidte ; the Empida?, 

 which follow them, scarcely aflect the early spring flora ; not far 

 behind come the busy gadding Muscid^e, among which the blue- 

 bottles (Calliphora) and little green Lucilia are particularly noticeable. 

 The remainder of the spring flies are of lower specialization as far 

 as a floral diet is concerned. Of other insects, Hemiptera live on 

 the juices of plants which they probe, and at times probe the 

 nectaries in the flowers ; some Coleoptera are regular flower-visitors, 

 but all are very simply organized in their mouth parts. Thysanoptera 

 are flower-loungers, just like the Ichneumons mentioned above, and 

 are more likely to eft'ect self- than cross-fertilization. Lastly, a few 

 Collembola visit flowers, apparently for the sake of the honey, and 

 certain crab-spiders, not for any part of the flower, but because 

 of the flies which they are able to catch. I liave several times 

 witnessed a struggle take place on the capitulum of a coltsfoot 

 between Xysticus and a Lucilia wliich had fallen into the open 

 claws of the spider. Krytluina is fertilized not by the flies which 

 visit it, but by the sun-birds which come to feed on the flies ; so, 

 too, ThssHcujo may now and then be fertilized through the agency of 

 this spider. For this reason — they are more efficient than Thrips — 

 I prefei- to include them as flower-visitors. 



Two things are necessary to the flower : firstly, efficiency in the 

 habits of the visitors, and, secondly, efficiency in their numbers. 

 The most desirable species of visitors are those which beyt combine 

 these two desiderata. In point of habit, Apis, Bombus, Andreija, 

 Lepidoptera, Syrphidic, Lmpida?, and perhaps Muscid;e are de- 

 sirable ; in point of numbers. Table I. shows that the Empidfe and 

 Lepidoptera must be excluded, and to some extent also Apis and 

 Bombus. 



Ahhreviations. — Hi., Hm., Hs. =-- long-, mid-, and short- 

 tongued Hymenoptera ; L. = Lepidoptera ; Dm. and Ds. = mid- 



* Throughout this paper I shall use the word Ichneumon to denote any of 

 the Terebrantia, and not the one genus of that name. 



