The red spider is not correctly speaking an insect, though it is commonly spoken of as such, neither is it a spider, as its name would imply, but an acarus or mite. Whether its name is correct or not, it is a most destructive and troublesome pest wherever it makes its presence felt, it by no means confines itself to one or only a few kinds of plants, as many insects do, but it is very indiscriminate in its choice of food, and it attacks both plants grown under glass and those in the open air. When these pests are present in large numbers, the leaves on which they feed soon present a sickly yellow or scorched appearance, for the supply of sap is drawn off by myriads of these little mites, which congregate on the under sides of the leaves, where they live in a very delicate web, which they spin, and multiply very rapidly; this web and the excrement of the red spider soon choke up the pores of the leaves, which, deprived of their proper amount of sap, and unable to procure the carbon from the atmosphere which they so much need, are soon in a sorry plight.
However promiscuous these mites may be in their choice of food plants - melons, cucumbers, kidney beans, hops, vines, apple, pear, plum, peach trees, limes, roses, laurustinus, cactuses, clover, ferns, orchids, and various stove and greenhouse plants being their particular favorites - they are by no means insensible to the difference between dryness and moisture. To the latter they have a most decided objection, and it is only in warm and dry situations that they give much trouble, and it is nearly always in dry seasons that plants, etc., out of doors suffer most from these pests. Fruit trees grown against walls are particularly liable to be attacked, since from their position the air round them is generally warm and dry, and the cracks and boles in the walls are favorite places for the red spider to shelter in, so that extra care should be taken to prevent them from being infested, this may best be effected by syringing the trees well night and morning with plain water, directing the water particularly to the under sides of the leaves, so as, if possible, to wash off the spiders and their webs.
If the trees be already attacked, adding soft soap and sulphur to the water will destroy them.
FIG. 1 - Red Spider (magnified). A 1. Ditto (natural size). 2. Underside of head. 3. Foot. 4. Spinneret.
Sulphur is one of the most efficient agents known for killing them, but it will not, however, mix properly with water in its ordinary form, but should be teated according to the following recipe:
Boil together in four gallons of water 1 lb. of flowers of sulphur and 2 lb. of fresh lime, and add 1½ lb. of soft soap, and, before using, 3 gallons more of water, or mix 4 oz of sulphate of lime with half that weight of soft soap, and, when well mixed, add 1 gallon of hot water. Use when cool enough to bear your hand in it. Any insecticide containing sulphur is useful. The walls should be well washed with some insecticide of this kind. Old walls in which the pointing is bad and the bricks full of nail holes, etc., are very difficult to keep free from red spider. They should be painted over with a strong solution of soot water mixed with clay to form a paint. To a gallon of this paint add 1 lb. of flowers of sulphur and 2 oz of soft soap.
This mixture should be thoroughly rubbed with a brush into every crack and crevice of the walls, and if applied regularly every year would probably prevent the trees from being badly attacked. As the red spider passes the winter under some shelter, frequently choosing stones, rubbish, etc., near the roots of the trees, keeping the ground near the trees clean and well cultivated will tend greatly to diminish their numbers. In vineries one of the best ways of destroying these creatures is to paint the hot water pipes with one part of fresh lime and two parts of flowers of sulphur mixed into a paint. If a flue is painted in this way, great care should be taken that the sulphur does not burn, or much damage may be done, as the flues may become much hotter than hot water pipes. During the earlier stages of growth keep the atmosphere moist and impregnated with ammonia by a layer of fresh stable litter, or by painting the hot water pipes with guano made into a paint, as long as the air in the house is kept moist there is not much danger of a bad attack. As soon as the leaves are off, the canes should be dressed with the recipe already given for painting the walls, and two inches or so of the surface soil removed and replaced with fresh and all the wood and iron work of the house well scrubbed.
If carnations are attacked, tying up some flowers of sulphur in a muslin bag and sulphuring the plants liberally, and washing them well in three days' time has been recommended.
Tobacco water and tobacco smoke will also kill these pests, but as neither tobacco nor sulphuring the hot water pipes can always be resorted to with safety in houses, by far the better way is to keep a sharp look out for this pest, and as soon as a plant is found to be attacked to at once clean it with an insecticide which it is known the plant will bear, and by this means prevent other plants from being infested. These little mites breed with astonishing rapidity, so that great care should be exercised in at once stopping an attack. A lady friend of mine had some castor oil plants growing in pots in a window which were badly attacked, and found that some lady-birds soon made short work of the mites and cleared the plants. The red spider lays its eggs among the threads of the web which it weaves over the under sides of the leaves; the eggs are round and white; the young spiders are hatched in about a week, and they very much resemble their parents in general appearance, but they have only three pairs of legs instead of four at first, and they do not acquire the fourth pair until they have changed their skins several times; they are, of course, much smaller in size, but are, however, in proportion just as destructive as the older ones.
They obtain the juices of the leaves by eating through the skin with their mandibles, and then thrusting in their probosces or suckers (Fig. 2), through which they draw out the juices. These little creatures are so transparent, that it is very difficult to make out all the details of their mouths accurately. The females are very fertile, and breed with great rapidity under favorable circumstances all the year round.
The red spiders, as I have already stated, are not real spiders, but belong to the family Acarina or mites, a family included in the same class (the arachnida) as the true spiders, from which they may be easily distinguished by the want of any apparent division between the head and thorax and body; in the true spiders the head and thorax are united together and form one piece, to which the body is joined by a slender waist. The arachnidae are followed by the myriapoda (centipedes, etc.), and these by the insectiae or true insects. The red spiders belong to the kind of mites called spinning mites, to distinguish them from those which do not form a web of any kind. It is not quite certain at present whether there is only one or more species of red spider; but this is immaterial to the horticulturist, as their habits and the means for their destruction are the same. The red spider (Tetranychus telarius - Fig. 1) is very minute, not measuring more than the sixtieth of an inch in length when full grown; their color is very variable, some individuals being nearly white, others greenish, or various shades of orange, and red. This variation in color probably depends somewhat on their age or food - the red ones are generally supposed to be the most mature.
The head is furnished with a pair of pointed mandibles, between which is a pointed beak or sucker (Fig. 2). The legs are eight in number; the two front pairs project forward and the other two backward; they are covered with long stiff hairs; the extremities of the feet are provided with long bent hairs, which are each terminated by a knob. The legs and feet appear to be only used in drawing out the threads and weaving the web. The thread is secreted by a nipple or spinneret (Fig. 4) situated near the apex of the body on the under side. The upper surface of the body is sparingly covered with long stiff hairs. - G.S.S., in The Garden.