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This paper reports general information obtained concerning the daily fluctuation of spider populations found in the cabbage fields in Fukuoka and Takanabe districts, the feeding of these on injurious crop insects, and the effect of Misumena tricuspidata (Fabricius) on them. The experiments or observations were carried out from September 3 to October 31 at Fukuoka and from November 10 to February 20, 1960, at Takanabe. A list of the species of spiders found to occur in the experimental cabbage fields is as follows : District of Fukuoka 1. Misumena tricuspidata (Fabricius). 2. Neoscona doenitzi (Boe. et Strand). 3. Lycosa t-insignita Biis. et Strand. 4. Agelena opulenta L. Koch. 5. Oxyopes sertatus L. Koch. 6. Lycosa sp. 7. Chiracanthium kompiricola Di.in. et Strand. 8. Theridiosoma eperioides Bos. et Strand. 9. Dolomedes herculus Bos. et Strand. 10. Plexippus crassipes Karsch. 11. Leucauge subblanda Bos. et Strand. 12. Hahnia cortcicola Bi.s. et Strand. District of Takanabe 1. Misumena tricuspidata (Fabricius). 2. Neoscona doenitzi (Bos. et Strand). 3. Lycosa 1-insignita Bcs. et Strand. 4. Leucauge subblanda Bos. et Strand. 5. Lycosa coelestis L. Koch. 6. Oxyopes sertatus L. Koch. 7. Plexippus paykulli (Audouin). 8. Tihellus tenellus (L. Koch). A list of the speci e s of insects caught by the spiders is as follows : a. Injurious insects of direct importance District of Fukuoka 1. Mamestra brassica Linne. 2. Agrotis fucosa Butler. 3. Agrotis ipsilon Hufnagel. 4. Prodenia litura Fabricius. 5. Mesographe forticalis Linne. 6. Udea testacea Butler. 7. Oebia undalis Fabricius. 8. Plusia jessica Butler. 9. Pieris rapae crucivora Boisduval. 10. Phytomyza atricornis Meigen. 11. Brevicoryne brassica Linne. 12. Nysius plebejus Distant. 13. Gryllulus mitratus Saussure. District of Takanabe 1. Phaedon brassica 13aly. 2. Phyllotre t a striolata Fabricius. 3. Oebia undalis Fabricius. 4. Plutella maculipennis Curtis. 5. Pieris rapae crucivora Boisduval. 6. Phytonryza atricornis Meigen. 7. Hylemyla platura Meigen. b. Injurious insects of indirect importance District of Fukuoka 1. Cnaphalocrocis medinalis Guenee. 2. Scopula modicaria Leech. 3. Adoxophyes orana Fis. von Ros. 4. Hymenia recurvalis Fabricius. 5. Nephotettix bipunctatus cincticeps Uhler. 6. Niraparvata lugens Linne. 7. Chlorita flavescens Fabricius. 8. Eutettix disciguttis Walker. 9. Cicadella viridis (Linne). 10. Musca domestica Linne. 11. Stomoxys calcitrans Linne. 12. Lucilia caesar Linne. 13. Paratettix histricus Stal. District of Takanabe 1. Acrolepia manganeutis Meyrik. 2. Illiberis pruni Dyar. 3. Erythroneura apicalis Nawa. 4. Empoasca onukii Matsuda. The present observations revealed that the effects of spiders on the cabbage pests were not neglizible. Especially Misumena tricuspidata was not only very effective but also very easy to make mass production in the laboratory. Thus Misumena tricuspidata may be regarded as a promising spider in the control of crop pests. Out of 140 individals of Misumena tricuspidata liberated 32 per cent were established in the cabbage field at Fukuoka, while out of 100 spiders liberated 60 per cent were established at Takanabe. This higher percentage of establishment seemed to be caused by the less active season of the spiders (at the end of November and throughout December), when the spiders became more sluggish before overwintering. During the course of experiments there was found no evidence that the spiders attacked the beneficial insects in the cabbage fields.