UNIVERSITY OF CALIFORNIA agricultural ExperimentStation 
 
 College of agriculture e. j. wickson, acting director 
 
 BERKELEY, CALIFORNIA 
 
 CIRCULAR No. 18 
 
 (February, 1906) 
 
 CATERPILLARS ON OAKS 
 
 BY 
 
 C. W. WOODWORTH. 
 
 The live-oaks about the Bay region of California are subject from 
 time to time to the attack of immense swarms of caterpillars, which 
 often entirely defoliate them, thus rendering them temporarily un- 
 sightly and contributing in no small measure to the death of the trees. 
 These losses can be entirely avoided, however, if the proper measures 
 are taken, and this circular is prepared to call attention to the methods 
 of accomplishing this work. 
 
 There are two species concerned, which have quite different habits 
 and present a somewhat different problem of control. 
 
 1. California Oak Caterpillar. 
 
 (Phryganidia calif omica, Pack.) 
 
 The insect bearing the above scientific name might be called the 
 "California oak caterpillar," since it is strictly limited, as far as 
 known, to this tree. It is a remarkable moth in many ways ; it is not 
 found outside of California, and is the only representative of its family 
 in America. The moth is pale gray in color with an expanse of wings 
 of about an inch, and can be seen sometimes in countless numbers 
 flying about oak trees, especially in the latter part of the day. They 
 are not strong of wing, but simply flutter about, alighting now and 
 then on leaves and then again taking to wing. During the night and 
 the larger part of the day most of the individuals will be found resting 
 quietly on the leaves. The length of life in this stage of its existence 
 is somewhere in the neighborhood of two weeks, during which time it 
 may lay two or three masses of eggs, or sometimes deposit all of its 
 eggs in one place. The under sides of the leaves are usually chosen for 
 egg laying. The eggs are about the size of a radish seed, yellow 
 in color at first but become darker as they develop, and finally the 
 caterpillar emerges and begins to feed upon the foliage. The first 
 
feeding is usually on the under side of the leaves and is noticeable on 
 the upper side only as pale spots due to the drying out of the leaf over 
 the denuded portion beneath caused by their feeding. Later, however, 
 when the caterpillars get larger, the leaf is eaten through except along 
 the larger veins, and thus becomes skeletonized. The leaves so eaten 
 usually soon drop from the tree, which thus becomes entirely devoid 
 of foliage. This may sometimes occur before the larger part of the 
 caterpillars have finished feeding, and they may die of starvation. 
 Usually, however, a good proportion of them find enough to bring 
 them to maturity. They then seek a suitable spot on the bark of the 
 tree and transform into a chrysalis, which is more like that of a but- 
 terfly than the form common in moths, and is entirely naked, not being 
 protected by silken coverings. This chrysalis is strikingly ornamented 
 with black marks and is really a very beautiful object. After a short 
 time in this stage the adult moth emerges, thus completing the cycle. 
 
 The remedy for this insect is to spray the trees with paris green, 
 using a mixture of one pound of paris green to two hundred gallons 
 of water. When the moths are seen fluttering about the tree in great 
 numbers immediate arrangements should be made for spraying the 
 trees, and strict watch maintained so as to recognize the first signs of 
 injury by the young worms produced from this brood of moths. As 
 soon as these worms are noticed the application should be made at 
 once and with great thoroughness, so as to place some of the poison in 
 reach of every caterpillar. If this is done the insects will be killed 
 before serious injury is occasioned and a single application will control 
 the difficulty. This has been demonstrated many times in many places, 
 so that there is no doubt of the efficiency of the treatment. In most 
 cases in the past, however, the mistake has been made of allowing the 
 caterpillar to become large, so that considerable damage is done to the 
 trees before any steps are taken toward controlling it. There should 
 be no difficulty, however, in following the directions here given, be- 
 cause the presence of the moth, which everybody recognizes, indicates 
 the approach of the injury and gives ample time for the preparations 
 for the work. 
 
 In spraying for this insect the only difficulty met with is that de- 
 pendent upon the size of the trees affected. It will usually be neces- 
 sary, in order to effectively spray, to provide ladders and send the 
 man using the nozzle into the highest parts of the tree, and to provide 
 him with a long extension rod enabling him to reach to every part, 
 since thorough work can be done in this way only. One should use a 
 spray nozzle giving a fine mist, and never attempt to spray a tree with 
 a nozzle which throws a stream, for thorough spraying cannot be ac- 
 complished in that way. All good spray nozzles are short-distance 
 nozzles and must be placed close to the parts of the tree when they are 
 being sprayed. Furthermore, in spraying these insects the trees should 
 never be allowed to drip, because after the leaves have been thoroughly 
 wetted with a fine mist any further application simply washes off the 
 poison which has already been placed on them, and a much less satis- 
 factory distribution of the poison results. 
 
Thorough spraying requires, then, first, the reaching of every part 
 of the tree ; second, the use of a spray nozzle giving a fine mist ; and, 
 third, the avoidance of drip. 
 
 The University is now experimenting with the use of especially 
 large sizes of extension rods with the hope of finding- satisfactory 
 means of handling rods that will reach the topmost parts of the tree, 
 avoid the use of ladders, and so simplify the spraying problem ; and 
 if the experiments prove successful the matter will be reported in full 
 in a bulletin of this Station, but there need be no failure to protect 
 the trees if one is sufficiently interested to give the necessary labor and 
 attention. 
 
 2. Tent Caterpillars. 
 Malacosoma, spp. 
 
 The above name applies to a series of moths, some six in number, 
 which are usually known by the term "tent caterpillar," because of 
 the peculiar habit of the young caterpillar of constructing silken tents 
 in which they live the larger part of the day, only going forth from 
 time to time to feed upon the leaves. The six species known to occur 
 in California are very similar in appearance and habits, though some 
 show such a remarkable amount of variation in color and pattern of 
 the wings of the moth, that they have received quite a number of 
 names, and a good many varieties are recognizable. 
 
 The insects are not strictly confined to the oak; indeed most, if 
 not all of them, are rather general feeders. In the Bay region the 
 live-oak leaf seems to be a favorite food, so that often they are se- 
 riously troublesome on the oak and scarcely noticeable on the other 
 trees. The moth is quite strictly a night flier and is not very com- 
 monly observed. The eggs are laid in a mass upon the small twigs, 
 usually forming a ring around the twig, though some times occurring 
 simply as a mass on one side of the branch. The eggs are somewhat 
 conical, set with the small end toward the twig and all firmly cemented, 
 so that the individual eggs are not usually easy to distinguish. These 
 insects are not at all infrequent on orchard trees all over the State, 
 and the egg masses are known to all orchardists who come across them 
 in pruning in the winter. The insects are all strictly one brooded, 
 passing the winter in the egg state. Quite early in the spring the 
 eggs hatch and the worms produced proceed at once to a crotch, usually 
 following down the twig and selecting the crotch where this twig joins 
 another, and there, all working together, build a tent of silk in which 
 they hide. This tent at first is quite small but is increased day by 
 day and serves as ample protection for the growing worms. When the 
 food is abundant the insects may spend the larger part of their life in 
 this tent, living together as a large family, going out in droves and feed- 
 ing together and returning again together to their tent ; but when food 
 is scarce the social instinct is gradually overcome and the insects may 
 be found wandering all over the trees, and leaving the tree to attack 
 other plants. In all cases when the insect is nearly full-grown this 
 wandering habit is assumed, even though the food may be ample ; and 
 
wherever they are abundant they become very conspicuous through 
 their habit of crawling over the ground, especially along paths and 
 sidewalks, and even crawling up sides of buildings. Finally they spin 
 cocoons over themselves, using the hairs that cover the body in addi- 
 tion to the silk which they spin, and then transform into the pupa 
 condition, from which somewhat later the moth emerges, and after 
 living its retiring life lays its mass of eggs and dies. 
 
 The control of this insect on smaller trees when not very abundant 
 can often be best accomplished by searching for the tents in the 
 crotches in the spring and the destruction of each colony. In the 
 Eastern States a chemist's test tube brush attached to the end of a 
 long pole is often used, by means of which the small tents can be 
 brushed out of the tree and brought down with their contents of small 
 worms. The use of a torch consisting of a rag tied in a ball at the end 
 of a pole and saturated with kerosene and set on fire has been quite 
 commonly used in California for the burning out of the tents, but is 
 no more rapid than the brush method and endangers the life of the 
 twigs. We would be rather inclined to use the pole pruning shears 
 and remove the twigs entirely, rather than to use the torch method. 
 When the insects are very abundant it will often be preferable to spray 
 the trees in the same way as for the preceding insect. The spray 
 method to be employed is exactly the same as for the Phryganidia, 
 and the timing of the spray should depend upon the observation of 
 the presence of the small tents produced by the newly hatched worms. 
 If the spraying is attended to while the tents are still small there will 
 be no appreciable damage to the trees, but if this matter is allowed to 
 go on until the insects are nearly full-grown there may not be enough 
 good accomplished in spraying to pay for the treatment. 
 
 Concluding Remarks. 
 
 The oak, which is our most beautiful native tree in central Cali- 
 fornia, should be protected from its insect enemies. This can be done 
 by spraying with paris green. Any kind of spray outfit will do, 
 though on account of the large size of the trees it would be distinctly 
 desirable to have the use of a power outfit. The maintenance of the 
 beauty of the shade trees is a community matter and it would be wise 
 for the Street Departments of cities to be provided with ample equip- 
 ment for making such applications. In villages and country places 
 the ordinary orchard spray outfit is already at hand and can be used. 
 Success will depend upon the thoroughness and the proper timing of 
 the treatments.