Charles Robertson.
Flower Visits of Insects II.
Psyche 31:93-111, 1924.

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19241 Flower Visits of Insects 11 93
FLOWER VISITS OF INSECTS 11.1
Carlinville, Illinois.
HYMENOPTERA (ex. bees).
The lower Hymenoptera, 26 per cent of the visitors observed, make only 16.8 per cent of the visits. Of the 437 insect flowers observed, they occur on only 43 per cent, while the bees occur on 95.4 per cent. The only respect in which they resemble the bees and show more efficiency than the flies and Lepidoptera is in the thick proboscides composed of several appendages, so that on many flowers they are more apt to transfer pollen. The flowers showing the greatest numbers of these insects are Cicuta maculata 145, Sium cicutoefoliurn 95, and Pastinaca sativa 91, with exposed nectar, and Pycnanthemum flexuosum 89, and Solidago canadensis 81, with concealed nectar. Of the visits of the lower Hymenoptera, 95.5 per cent are to social flowers, usually with epigynous nectaries. It is held here that these insects have produced no special flowers. They
resort to highly specialized social flowers which have been mod- ified by bees. They may have had some influence in further modifying these, especially in the case of fig flowers. The ecology of lower Hymenoptera is associated with insects on which they are parasitic or with which they provision their nests. They are therefore most abundant in summer when all except Tenthredinidae reach their maxima. They have no The first number was published in Psyche 30: 158-69, 1923. In the
table on page 158 the local flora should be 560, with percentages as follows: Ma 27.5, Mi 28.9, Mas 17.3, Mis 21.4, Pol 4.8, Red 29.4, White 39.8, Yellow 30.7. Of the 493 indigenous flowers the percentages are: Ma 25.9, Mi 29.6, Mas 17.0, Mis 22.7, Pol 4.6, Red 29.0, White 40.3, Yellow 30.6. On page 1.59, line 4, for "41.6" read "about 48". In line 32 "ruby-throated" came from an abortive attempt to shorten "ruby-throated humming-bird" to "ruby- throat."
On page 167, line 24, for "seventy" read "seventy-three." Besides
the tables mentioned there, each one of the 1288 visitors has its visits dis- tributed under the classes and colors as shown in 3, 173. Pu&f 31:93-111 t l!XU). hqxYipsyche mtclub ore/31i31-093 hlml



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94 Psyche [April
relation to flowers except to visit those which suit them and are in bloom when they fly. They make fewer non-pollinating visits than any other of the general groups. Bembicidoe.-Of 99 visits of 10 species to 49 flowers, 39.3 per cent are to Mis, 32.3 to Mas, 28.2 to Pol, 52.5 to white, 34.5 to yellow, 37.3 to Compositse, 20.2 to Labiatse and 13.1 to Um- belliferse.
All visits are to social flowers.
Sphecidm-Of 377 visits of 16 species to 110 flowers, 43.2 per cent are to Mis, 27.8 to Mas, 27.3 to Pol, 53.3 to white, 33.4 to Compositse, 14.8 to Labiatse and 13.5 to Umbelliferae. Pol. shows 15.4 per cent of the flowers visited. Sco1iidce.-Of 133 visits of 7 species to 69 flowers, 45.8 per cent are to Mis, 29.3 to Pol, 20.3 to Mas, 61.6 to white, 31.5 to Compositse, 15.7 to Labiatse and 12.7 to Umbelliferae. This and the two preceding are the only families of wasps showing more than 18.7 per cent of visits under Mas. Eumenidoe.-Of 461 visits of 31 species to 109 flowers, 62.9 per cent are to Mis, 21.0 to Pol, 60.0 to white, 32.7 to yellow, 33.1 to Compositse and 22.3 to Umbelliferse. Philanthidoe (including Cerceridse) .-Of 182 visits of 16 species to 63 flowers, 54.9 per cent are to Mis, 34.0 to Pol, 67.5 to white, 30.2 to Compositse, 16.4 to Umbelliferse and 12.6 to Labiatse.
Pol is 23.8 per cent of flowers visited. Crabronida-Of 253 visits of 27 species to 69 flowers, 49.4 per cent are to Mis, 44. 2 to Pol, 68.3 to white, 39.9 to Um- belliferse and 26.8 to Compositse. Pol shows 21.7 per cent of the flowers visited.
Vespidce.-Of 182 visits of 8 species to 82 flowers, 56 per cent are to Mis, 26.3 to Pol, 59.3 to white, 39.5 to Compositse and 13.7 to Umbelliferse.
Chrysididoe.-Of 64 visits of 17 species to 35 flowers, 50 per cent are to Mis, 46.8 to Pol, 81.2 to white, 45.3 to Umbelliferse and 25.0 to Compositse. Of flowers visited, Mis shows 65.7 and Pol 31 .4 per cent.




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19241 Flower Visits of Insects 11 95
Larridce.-Of 105 visits of 19 species to 42 flowers, 50.4 per cent are to Pol, 45.7 to Mis, 80.9 to white, 33.3 to Umbelliferse, 20.0 to Compositse and 16.2 to Labiatse. Of the flowers visited, 57.1 per cent belong to Mis and 33.3 to Pol. Tiphiid-Of 19 visits of 4 species to 14 flowers, 52.6 per cent areto Pol, 42.1 to Mis, 64.4 to white, 31.5 to yellow, 78.9 to Umbelliferse and 15.7 to Compositse. Of flowers visited, 50 per cent belong to Mis, 42.8 to Pol and 42.8 to yellow. Pompi1idce.-Of 188 visits of 33 species to 47 flowers, 58.5 per cent are to Pol, 36.7 to Mis, 70.7 to white, 39.3 to Um- belliferse and 19.1 to Compositse. Pol shows 36.1 per cent of the flowers and Mis 48.9
Nyssonidce, Pemphredonidce, Thynnidce, Trypoxylonidce, Be- thylidce, Myrmosidce, Formicidce male, Mutillidce male.-Of 48 visits of 22 species to 20 flowers, 75 per cent are to Pol, 79.1 to white, 65.9 to Umbelliferse and 10.6 to Compositse. Pol shows 50 per cent of the flowers and Mis 40.0. Wasps-Of 2111 visits of 210 species to 1.82 flowers, 49.5 per cent are to Mis, 34.4 to Pol, 63.5 to white, 30.0 to Com- positse, 24.8 to Umbelliferse and 10.5 to Labiatse. Of 825 visits of the Philanthidse, Eumenidse and Vespidse, 59.6 per cent are to Mis. Of 677 visits of Crabronidse and the last five groups, 51.8 per cent are to Pol. Of 574 visits before July, the wasps show 46.6 per cent to Mis, 39.3 to Pol, 54.7 to white and 37.6 to yellow, while of 1570 visits after June they show 50 per cent to Mis, 32.9 to Pol, 65.8 to white and 25.2 to yellow. The maximum shifts from A 35.1 to B' 36.7. Of the visits of Sco- liidse, Sp hecidse, Bembicidse, Philanthidse and Vespidse, 13.9; of Eumenidse, 22.3; and of Larridse, Tiphiidse, Pompilidse, Crabronidse, Nyssonidse and Chrysididse, 42.2 per cent are to Umbelliferse. Of the visits of Scoliidse, Sphecidse, Bembicidse, Philanthidse and Larridse, 15.2 per cent are to Labiatse. Ichneumonidce.-Of 79 visits of 45 species to 35 flowers, 53.1 per cent are to Pol, 37.9 to Mis, 50.6 to yellow, 49.3 to white, 51.8 to Umbelliferse and 30.3 to Compositse. Of the flowers, 54.2 per cent are Mis, 28.5 Pol, 54.2 white and 45.7 yellow.



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96 Psyche [April
Braconid@.-Of 58 visits of 33 species to 23 flowers, 51.7 per cent are to Pol, 32.7 to Mis, 58.8 to white, 41.3 to yellow, 53.3 to Umbelliferse and 32.7 to Compositse. Chalcidoidea, Figitidce, Evaniidce.-Of 85 visits of 33 species to 25 flowers, 76.4 per cent are to Pol, 75.2 to white and 78.8 to Umbelliferse.
Tenthredinid@.-Of 27 visits of 14 species to 15 flowers, 59.2 per cent are to Mis, 33.3 to Pol, 70.3 to yellow, 40.7 to SaUx and 11.1 to Umbelliferse.
Non-aculeata.-Of 249 visits of 125 species to 62 flowers, 58.6 per cent are to Pol, 33.3 to Mis, 61.7 to white, 37.8 to yellow, 57.2 to Umbelliferse and 20.8 to Compositse. Before July 59.8 per cent of the visits are to yellow and 40.1 to white; after June 76.1 are to white and 23.0. to yellow. The maxima remain under A and Pol, but shift from yellow to white. The preference is for flowers with exposed nectar and most of the visits are to them in spite of the dominance of other classes. So that exposed nectar as a determining condition, is limited to a few visits of the most insignificant of hymenopterous pollinators. Even then it fails except when the flowers are social. Many visitors should probably be left out, being so minute as to be of doubtful value, even if all other guests were excluded. Lower Hymenoptera.-Of 2360 visits of 335 species to 188 flowers, 47.8 per cent are to Mis, 37.0 to Pol, 62.9 to white, 95.5 to social flowers, 29.0 to Compositse and 28.2 to Umbelli- ferse.
Pol shows 11.1 per cent of the flowers visited. Of 28 non-pollinating visits 19 are to Mas and 22 to red. Visits to red are 7.5 per cent compared with 18.8 for the Alps. Ten prefer Mas, 112 Mis, 206 Pol, 240 white and 89 yellow. After June the maximum changes from A 40.6 to B' 36.7. Yellow changes from 41.5 to 25.0.
Midaid@.-Two species prefer Pol and white. Nemestrinidas.-The single species prefers Mas and red.



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19241 Flower Visits of Insect 11 97
Bornbyliidce.-Of 370 visits of 28 species to 160 flowers, 45.6 per cent are to Mas, 31.6 to Mis, 38.3 to yellow and 50.8 to Compositse. Of the flowers visited, 35.0 belong to Mas and 28.1 to yellow. Visits to red are 23.7 compared with 75.0 in the Alps. After June the maxima change from fib 27.7 to B' 66.0, Mis 31.9 to Mas 58 .O, white 52.9 to yellow 43.5. Conopidce.-Of 238 visits of 15 species to 115 flowers, 47 per cent are to Mis, 25.6 to Mas, 20.1 to Pol, 56.3 to white, 10.9 to Labiatse, 14.2 to Umbelliferae and 32.3 to Compositse. Red shows 13.8 compared with 44.4 in the Alps. After June the maximum shifts from AB 29.9 to B' 43.6. Mas changes from 14.7 to 35.9, yellow from 35.2 to 25.3 and red from 9.8 to 19.0. Syrphida-Of 1165 visits of 86 species to 203 flowers, 51.5 per cent are to Mis, 20.0 to Pol, 58.8 to white, 33.9 to yellow, 24.4 to Composites and 17.8 to Umbellifer&. Red shows 7.2, in the Alps 29.3. After June the maximum changes from AB 37.8 to B' 47.5. Mi changes from 22.2 to 7.8, Mas from 2.1 to 22.9, yellow from 39.2 to 29.0.
The importance of these flies as pollinators has been greatly exaggerated. The general habit of pollen-eating is shown from the fact that the proboscis is never modified so as to prevent it. In 104 visits of Syrphidse to diclinous flowers 31.7 per cent were to pistillate, and 68.2 to staminate, flowers. This shows pretty decisively their preference for pollen. They make more non- pollinating visits than are made by all other flies together. Of 145 visits of this kind 50.3 per cent are to Ma and 42.7 to red. The flowers showing the greatest number of Syrphidse are Sassafras variifolium 19, Salix cordata 22, Solidago canadensis 22, Pastinaca sativa 26, Aster ericoides villosus 30, Heracleum lanatum 32.
Empidid&.-Of 162 visits of 24 species to 87 flowers, 48.1 per cent are to Mis, 25.3 to Pol, 60.4 to white, 31.4 to yellow, 12.3 to Roascese, 15.4 to Compositse and 16.0 to Umbelliferse. Pol shows 12.6 per cent of the flowers visited. Red shows 8 per
cent of the visits, in the Alps 30.1. After June the maximum changes from A 38.5 to B' 57.5. The siphonate proboscis was



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98 Psyche [April
evidently developed as a predaceous organ, but is also used for sucking nectar. Parempis clausa is evidently exclusively an- thophilous. It flies 113 days after all of the other species have disappeared. Being 4 per cent of the species, it makes 27 per cent of the visits.
Stratiomyidce.-Of 53 visits of 13 species to 36 flowers, 45.2 per cent are to Mis, 43.3 to Pol, 60.3 to white, 35.8 to yellow and 41.5 to Umbelliferse. Red shows 3.7, in the Alps 40.0. Tachinida-Of 842 visits of 108 species to 158 flowers, 53.4 per cent are to Mis, 29.8 to Pol, 66.5 to white, 25.2 to Umbelliferse and 33.9 to Compositse. After June the maximum shifts from A 37.5 to B' 46.3.
White changes from 59.3 to
70.1 and yellow from 37.5 to 26.0.
Other Ca1yptratce.-Of 692 visits of 50 species to 140 flowers, 48.2 per cent are to Mis, 29.6 to Pol and 64.5 to white. Of total Calyptratse visits, 23 per cent are to Umbelliferse and 25.5 to Compositse.
Aca1yptratce.-Of 178 visits of 53 species to 59 flowers, 47.1 per cent are to Pol, 43.8 to Mis, 55.0 to white, 43.8 to yellow, 58.4 to Umbelliferse and 12.3 to Compositse. Muscoidea.-Of 1712 visits of 211 species to 191 flowers, 50.3 per cent are to Mis, 31.6 to Pol, 64.3 to white, 31.7 to yellow, 26.6 to Umbelliferse and 28.3 to Compositse. Pol is 12 per cent of flowers visited. Red shows 3.9 per cent of the visits, to 14.1 in the Alps. They are probably more important to flowers than the Syrphidse, since they are usually aftel* nectar. Of the total fly visits 45.3 per cent are made by Muscoidea and 30.8 by Syrphidz.
Tabanidce, Scenopinidce, Pipunculidoe, Leptidce, Phoridoe.- Of 18 visits of 9 species to 13 flowers, 77.7 per cent are to Pol. 72.2 to white and 72.2 to Umbelliferge.
Nematocera.-Of 44 visits of 15 species to 24 flowers, 50 per cent are to Pol, 56.8 to white, 43.1 to yellow and 50.0 to Umbelliferse. These flies are usually associated with more



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19241 Flower Visits of Insects II 99
efficient pollinators and often are so small that they can get the nectar without much probability of touching the anthers and stigmas.
Diptera-Of 3775 visits of 403 species to 266 flowers, 48 per cent are to Mis, 25.4 to Pol, 59.3 to white, 32.9 to yellow, 21.8 to Umbelliferse and 28.2 to Compositse. Mis shows 31.9 per cent of the flowers, Pol 8.6 and white 46.9. One prefers Ma, six prefer Mi, 21 Mas, 158 Pol, 192 Mis, 9 red, 133 yellow, 253 white. Visits to red are 7.7, Alps 22.2, Low Germany 24.2. Berlin Garden 33.1. After June the maximum changes from A 35.4 to B' 48.1. Yellow changes from 37.7 to 28.3. Of 256
non-pollinatingvisits, 32.8 are to Ma, 21.0 to Mas, 17.0 to Pol and 38.6 to red.
Next to bees, flies visit more species of flowers andmake more visits than any other anthophilous insects. Being 31.2 per cent of the species, they make 27 per cent of the visits, 36.8 per cent of the total visits to Pol. The total number of flowers visited is less than that for Bombidse or Halictidse. The flowers visited by 62 or more flies are Solidago canadensis 62, Zizia aurea 63, Sium cicutcejolium 71, Cicuta maculata 82, Pastinaca saliva 113, Heracleum lanatum 121, Aster ericoides villosus 12 1.. The flowers showing the greatest number of siphonate flies are Solidago canadensis 16, Boltonia asteroides 18, Bidens aristosa 21, Pycmnthemum flexuosum 22, Eryngium yuccifolium 23 and Aster ericoides villosus 31.
The importance of flies as pollinators is greatly exaggerated. They are apt to show as the exclusive visitors in unfavorable weather, or in localities where the flora and insect fauna have been greatly disturbed. The proboscis is usually rather thick SO that the pollen readily touches and adheres to it, but the more highly specialized for probing flowers it becomes, the less likely it is to extract the pollen. In the lists have been admitted flies which should probably be excluded on account of their small size, or ability to extract nectar or eat pollen without effecting pollination.




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Some flies have taken possession of some non-social flowers which have become adapted to flesh-flies or minute flies. The
flowers which the Diptera prefer, however, are highly specialized social flowers, usually with epigynous nectaries, 86.3 per cent of the visits being to social flowers.
Sphingidm-Of 22 visits of 7 species to 15 flowers, 54.5 per cent are to Ma, 40.9 to Mas, 63.6 to red, 45.4 to Polemoniales and 13.6 to Labiatse. In the Alps visits to red are 63.2. Other Heterocera-Of 106 visits of 21 species to 68 flowers, 47.1 per cent tire to Mid, 31.1 to Mas, 10.3 to Pol, 48.1 to white, 34.9 to yellow and 57.5 to Compositse. Red shows 16.9, in the Alps 58.6.
Rhopa1ocera.-Of 1065 visits of 67 species to 203 flowers, $3.6 per cent are to Mas, 24.3 to Mis, 38.3 to red, 11.0 to Labiatse and 36.3 to Compositse. In the Alps red shows 55.2. Lepidoptera.-Of 1193 visits of 95 species to 211 flowers, 42.4 per cent are to Mas, 25.9 to Mis, 39.3 to white, 36.8 to red. In the Alps red shows 56.1, Berlin Garden 64.0, Low Germany 70.2. One prefers Mi, 7 Ma, 12 Pol, 22 Mis, 51 Mas, 46 red, 33 white, 16 yellow. Of 175 non-pollinating visits, 52.5 per cent are to Ma, 34.2 to Mas and 57.1 to red. Before July they prefer Mas and red; after June, Mas, Mis, Pol, white and red.
The maximum changes from Hb 32.6 to B' 50.1. Visits to non-social flowers change from 48.2 to 7.2. The structure of the proboscis seems to indicate that the butterflies not only had little, or nothing, to do with the origin of insect flowers but that they did not come into existence until after the highly specialized bee flowers had been developed. The moths are important visitors of few flowers and have in- fluenced the development of few, except in the case of the Sphingidse. Butterflies are large and correspond little with the variable sizes of flowers. Their proboscides average long, so that they are usually able to reach the nectar of the deepest bee flowers. Their relations to flowers are often that of nectar



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19241 Flower Visits .of Insects II 101
thieves. The proboscis is exceedingly slender, smooth and dry so that it often does not touch the pollen, or does not readily hold it. On flowers with exserted anthers and stigmas the butter- flies are probably the most useful. But even in such cases they often insert their tongues into flowers whose anthers and stigmas they do not touch with their bodies. It is a regular thing for them to visit personate and papilionaceous flowers without any likelihood of touching the anthers. In slender tubed flowers with included anthers they may touch the anthers, but even here there is doubt about much pollen sticking to their tongues. There are probably no slender-tubed butterfly flowers from which bees are excluded and in which bees are not likely to be more useful. A bee's proboscis has from five to seven appen- dages wet with nectar or honey, and which get so covered with pollen that in mounting it is often necessary to wash the pollen out.
In the percentage of visits, 8.5, over species, 7.3, the Lep- idoptera show a slight gain, but in 41 flowers whose visitors were taken as they came they lost in percentage of individuals. Co1eoptera.-Of 438 visits of 137 species to 113 flowers, 42.4 per cent are to Mis, 40.8 to Pol, 64.8 to white, 15.2 to Com- posits and 39.4 to Umbelliferse. One prefers Mas, 48 Mis, 81 Pol, 46 yellow and 88 white. Visits to red are 5.2, in the Berlin Garden 16.9, Low Germany 18.3, Alps 23.2. Of 123 non- pollinating visits, 34.9 per cent are to Mis, 30.0 to Mas and 40.6 to yellow. After June the maximum changes from A 50.9 to B7 46.2.
The flowers showing the greatest number of beetles are Pastinam sativa 42, Aruncus sylvester 33, Cryptotcenia canadensis 19, sum, cicutwfolium 19.
Beetles seem to have developed anthophilous habits as a secondary matter, and were probably few on primitive flowers. Some have structures fitting them for obtaining nectar, as



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102 Psyche [April
Chauliognathus pennsylvanicus, which has maxillary lobes ex- tensile by 4 or 5 mm, and makes more visits than any other beetle.
Beetles probably have produced no special flowers. They
principally resort to social flowers with epigynous nectaries. Hemiptera.-Of 113 visits of 21 species to 64 flowers, 47.7 per cent are to Mis, 30.9 to Pol, 52.2 to white, 38.0 to yellow, 34.5 to Compositse and 30.9 to Umbelliferse. Ten prefer Mis,
eight Pol, 11 white and ten yellow. After June yellow changes from 47.1 to 29.0. The maximum shifts from B 39.6 to B' 50.0. The proboscis, though not developed for flower visits, is sometimes used to extract nectar.
The Hemiptera and Coleoptera form 12.2 per cent of the visitors observed, but make only 3.9 per cent of the visits. Newoptera.-Chrysopa plorabunda, found on some Um- belliferse with exposed nectar, is not included in the tables. Birds.-Of 29
visits made by the rubythroat, 82.7 per
cent are to Ma, 55.1 to red, 17.2 to Personales, 13.7 to Labiatse, 13.7 to Leguminosse, 10.3 to Polemoniales. It picks out the most highly modified and brightest colored of the long-tongued bee flowers. The bird flowers belong to melittophilous groups and have been appropriated by the humming-birds. Total Visitors-Of 13971 visits made by 1288 visitors to 437 flowers, 39.8 per cent are to Mis, 20.4 to Mas, 18.7 to Pol, 51.3 to white, 31.7 to yellow, 28.9 to Compositse and 15.9 to Umbelliferse. Thirty-six pefer Mi, 44 Ma, 176 Mas, 471 Pol, 511 Mis, 126 red, 390 yellow and 755 white. After June visits to Mas change from 8.3 to 32.7, to yellow from 34.2 to 29.9, and the maximum changes from AB 26.8 to B' 44.6. Visits to red are 16.8 per cent, in the Alps 41 .6.
Loew's Groups.-If the flower classes A, AB and Po are designated as allotropic, B and B^ as hemitropic, and Hb, I? and 0 as eutropic, and the insects are classed according to the kinds



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19241 Flower Visits of Insects 103
of flowers which they visit, it will be found that those which before July are eutropic, hemitropic or allotropic, are hemitropic after June. Really the highest specialized and latest developed flowers and insects are hemitropic.
Specialization for obtaining Nectar.-The rubythroat, the Lepidoptera, long-tongued bees and some siphonate flies can visit a great many flowers from which short-tongued bees are excluded. They are at some disadvantage on flowers with shallow nectar.
Muller (3,58) states that A pis and Bombus play by far the most important part in the fertilization of German indigenous flowers. Knuth (2,154) says : "Just as the pollen-collecting apparatus has reached its highest degree of development in Apis and Bombus, so also has the mouth of the bees become '
best adapted for rifling the nectar of flowers. It is therefore
intelligible that bees belonging to these two genera play a far more important part than any other insects in the pollination of our indigenous flowers." When these bees are compared with other bees having a similar flight, the importance of the special- ization of the proboscis and scopa is not so obvious. When 40 species of Halictidse make nearly as many visits as 133 species of long-tongued bees, it is not on account of a more highly special- ized tongue or scopa. The Halictidoe visit 14 more flowers and make 1123 more visits than the Bombinse, 927 more than Bom- bin% and Apis together. When Apis and Bombus make only 13.3 per cent of the visits recorded in Muller's Fertilisation of flowers, it is not easy to understand these statements regarding their importance in pollination.
Dependence on a Floral Diet.-The food of bees is almost ex- clusively from flowers. The fig chalcids and Pronuba are about the only insects which can compare with them. The importance to flowers of the nest-provisioning habit is shown by the fact that the nest-making bees average 23.4 visits, while the in- quilines average 10.7. The females of the nest-makers average 20.6 visits, while the males average 10.3. The females of the inquilines average 8.8 and the males 8.0.



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104 Psyche [April
Numb.er of Species.-On account of having more species, and in spite of a lower average number of visits, the flies and lower Hymenoptera surpass the Lepidoptera; the Halictidse and Megachilidse surpass the Bombidse; the Andrenidse surpass the Euceridse; the Muscoidea surpass the Syrphidse; the Syrphidse and Bombyliidse surpass the Conopidse; the Eumenidse surpass the Sphecidse, Vespidse and Scoliidse; the Crabronidse and Pom- pilidse surpass the Vespidse, Philanthidse, Scoliidse and Bembicidse. Average Number of Visits.-In spite of the fewer species, the bees surpass the flies in average number of visits. The Bombinse surpass the Euceridse, Megachilini, Nomadidse, Osmiini or Epeolidse which have more species. The Halictidse make 1366 more visits than the Andrenidse, although they have only five more species.
Length of Flight.-The high average for Apis rnellifera, Bombinse, Ceratinidse, Halictidse and Vespidse is associated with the long flight, the most important condition determining