744 



HORTICULTURE 



May 27. 1916 



THE RED SPIDER 



(An Address by Parker Thayer Barnes before the Florists' Club of 



PhiLidelphin. M.iy 2. 1916 i 



The red spider is a pesky pest with 

 which every person who grows plants 

 under gloss has a tussle sooner or 

 later, usually sooner. It also gives 

 much trouble at times to shade and 

 even fruit trees. There really seems 

 to be no limit to which its ramifica- 

 tions extend. 



The red spiders are mites. They 

 belong to the great class of Arachnida 

 (A-rach'ni-da) to which spiders, scor- 

 pions and the daddy-long-legs belong. 

 They bear to the more highly devel- 

 oped and complex insects, such as the 

 moths and flies, a position somewhat 

 similar to that of the ferns to flow- 

 ering plants, although this is rather a 

 poor simile. 



The red spider Is not a new insect 

 in any way one may look at it. New- 

 species are being found from time to 

 time but that is because but few spe- 

 cialists have worked on this branch 

 of the animal kingdom, and they are 

 so much alike that it is really hard to 

 distinguish them. They have four 

 pairs of legs, only three when born, 

 but the other pair develops while they 

 are young. 



They winter over outside under 

 stones and in leaves and other rubbish 

 and when warm weather returns — 

 about the time the leaves appear — 

 climb the trees or other plants and 

 start laying eggs. Each female can 

 lay from five to ten eggs a day for a 

 period of eight to twelve days. In five 

 days they become adults. Brood 

 after brood is produced all summer — 

 but wet weather sometimes interferes. 



Much the same conditions exist in 

 the greenhouse except that the 

 spiders do not hibernate because it is 

 warm there the year around. 



The mites do not travel fast except 

 when disturbed; ordinarily they move 

 slowly, and for a greater portion of 

 the time they are stationary, sucking 

 the sap from the leaf on which they 

 are resting. The removal of the sap 

 from the cell causes the cell to dry 

 out and die which gives it that pe- 

 culiar look always associated with a 

 severe attack. A similar appearance 

 is caused in the fruit trees sometimes 

 by a little leafhopper. 



The genus of mites which contains 

 the common red spider is Tetranychus 

 and all the members of this genus 

 spin a very fine thread. In severe at- 

 tacks these threads are so abundant 

 as to form a web, either upon the up- 

 per or lower surfaces of the leaves or 

 covering the branch or a number of 

 leaves. I have seen this occur in 

 greenhouses where things were al- 

 lowed to run in a haphazard way. The 

 use of this web nobody seems to un- 

 derstand. It alTords no protection to 

 the mites. Dr. Baules suggests that 

 its chief use is to hold the eggs while 



another scicnlisi sii^Ki^'sl.'^ that it 

 keeps them from fulling olT the plant 

 while they are molting. Experi- 

 ments have proven that it does not in 

 any way serve to aid their progress. 



The spinning organs which produe- 

 this web are supposed to be situated 

 in the head, the threads coming out 

 tlirough the palpi or feelers, but some 

 very delicate dissection work under a 

 high-powered microscope is still neces- 

 sary to locate the red spider's si>ln- 

 ning. 



The common species of the green- 

 houses is T. bimaculatus. It is sup- 

 posed to be red in color but any one 

 who has ever examined them under 

 a hand lens knows that some of them 

 have a washed out color, much like 

 tlie crushed strawberry colored shirt 

 that has gone through the laundry. 

 Hut the color does not vary in a col- 

 ony; all of one colony are the same 

 shade of color. 



This species is by no means con- 

 fined to greenhouses as I have already 

 intimated nor to our northern climate. 

 It is common in the south, at first on 

 violets but it has now spread from 

 this humble plant to the cotton plant. 

 On this it works such damage that it 

 has been necessary for the Federal 

 Bureau of Entomology to detail men 

 to learn how it ran be easily and 

 cheaply combated. In California it 

 has threatened the hops crop and 

 again the government has come to the 

 aid of the beer drinkers and saved 

 the backbone of their staple beverage. 

 FYoin this you can see that the grower 

 of plants under glass is not the only 

 sufferer from the mites or red spider. 



The orange groves of Florida and 

 California are infested with a couple 

 of species. It was a serious pest as 

 far back as 1889. for the Report of the 

 Entomologist of the U. S. Department 

 of Agriculture of that year reports it 

 as a menace to the crop. 



A pale greenish species. T. praten- 

 sis. is abundant in the west on afalfa 

 and other crops. A bright red species 

 T. opuntiae plays hide-and-seek on the 

 prickly pears of Texas. A very short- 

 legged short-haired European species 

 is found on the spruce tree of Canada. 

 Another snecies is common on the 

 leaves of the oak and chestnut, and a 

 comparatively newcomer from Europe 

 is T. pelouse which much prefers the 

 fruit trees of our orchards. The Euro- 

 pean plum seems to be the favorite 

 food plant of this species. 



•The array of species is no doubt un- 

 interesting and to the average person 

 a red spider is a red spider and just 

 as much of a pest as Elias Butler 

 Parker's guinea pigs of "Pigs is Pigs" 

 fame. 



How are we to get rid of them? 

 That's the question and I suppose It 

 was upon this point that our friend 

 Watson hung the word explosion — "A 

 Red Spider Explosion." He thought 

 that maybe I would blast all your pre- 

 conceived ideas about the subject of 

 red spiders. 



The first thing I learned about red 

 spider while serving my novitiate in 



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the greenhouse was that as the cold 

 of winter begins to strengthen mak- 

 ing hard firing necessary, with the re- 

 sulting drier air the red spider com- 

 menced to flourish and so we all 

 believed that an arid condition was 

 congenial to the red spider. 1 suppose 

 U is in a measure, but it is not ab- 

 solutely necessary. Last summer was 

 far from being a dry summer, there 

 were no long droughts in it, and yet 1 

 found red spider infesting shade trees 

 in the vicinity of llarrisburg to such 

 an extent that the trees had lost their 

 green color, and had taken on a grey- 

 ish or brownish color which gave 

 them the appearance of much road 

 dust having settled upon their sur- 

 faces. 



We were taught that water was the 

 only specific. It will wash them off, 

 but do they have time tcf drown before 

 the water has drained away from the 

 soil where they fell under the plant, 

 and so are they or are they not ready 

 to crawl back on the plant. I do not 

 know. I have not had suflieient time 

 to watch them to find out. 



Sulphur is the one best bet with 

 which to fight the pest. You can blow 

 it on by means of a blow gun; you 

 can use lime-sulphur wash such as is 

 used to kill the San Jos4 scale on the 

 fruit trees, but of course, very much 

 weaker, or you can use potassi\im sul- 

 phite (Liver of sulphur) one-half ounce 

 to the gallon of water. This last you 

 will all probably recognize as a stand- 

 ard remedy for mildew on roses. 



Instead of blowing the sulphur on 

 you can spray it on. One pound of 

 sulphur mixed in three gallons of 

 water and just enough soap to make 

 it stick is a standard remedy on fruit 

 trees as a summer spray, but in the 

 greenhouse I would use it much weak- 

 er at first to make sure of not burning 

 the foliage. 



Prof. S. T. Maynard reports having 

 successfully killed the red spider in a 

 house of grapes by boiling the sulphur 

 but this is a rather dangerous and 

 tedious method. 



If I was called upon today to fight 

 a case of red spider in a greenhouse or 

 on fruit trees, T would do one of two 

 things. The first thing would be to 

 spray the plants with a flour paste. 

 That sounds like a very reckless 



