Handbook of Medical Entomology Part 5

[Ill.u.s.tration: 28. The poison apparatus of Formica. Wheeler, after Forel.]

OTHER STINGING FORMS--Of the five thousand, or more, species of bees, most possess a sting and poison apparatus and some of the larger forms are capable of inflicting a much more painful sting than that of the common honey-bee. In fact, some, like the b.u.mble bees, possess the advantage that they do not lose the sting from once using it, but are capable of driving it in repeatedly. In the tropics there are found many species of stingless bees but these are noted for their united efforts to drive away intruders by biting. Certain species possess a very irritating saliva which they inject into the wounds.

The ants are not ordinarily regarded as worthy of consideration under the heading of "stinging insects" but as a matter of fact, most of them possess well developed stings and some of them, especially in the tropics, are very justly feared. Even those which lack the sting possess well-developed poison glands and the parts of the entire stinging apparatus, in so far as it is developed in the various species, may readily be h.o.m.ologized with those of the honey-bee.

The ants lacking a sting are those of the subfamily CAMPONOTINae, which includes the largest of our local species. It is an interesting fact that some of these species possess the largest poison glands and reservoir (fig. 28) and it is found that when they attack an enemy they bring the tip of the abdomen forward and spray the poison in such a way that it is introduced into the wound made by the powerful mandibles.

[Ill.u.s.tration: 29. A harmless, but much feared larva, the "tomato worm."

Natural size. Photograph by M. V. S.]

More feared than any of the other Hymenoptera are the hornets and wasps.

Of these there are many species, some of which attain a large size and are truly formidable. Phisalix (1897), has made a study of the venom of the common hornet and finds that, like the poison of the honey-bee, it is neither an alb.u.minoid nor an alkaloid. Its toxic properties are destroyed at 120 C. Phisalix also says that the venom is soluble in alcohol. If this be true, it differs in this respect from that of the bee. An interesting phase of the work of Phisalix is that several of her experiments go to show that the venom of hornets acts as a vaccine against that of vipers.

NETTLING INSECTS

So far, we have considered insects which possess poison glands connected with the mouth-parts or a special sting and which actively inject their poison into man. There remain to be considered those insects which possess poisonous hairs or body fluids which, under favorable circ.u.mstances, may act as poisons. To the first of these belong primarily the larvae of certain Lepidoptera.

LEPIDOPTERA

[Ill.u.s.tration: 30. Another innocent but much maligned caterpillar, the larva of the Regal moth. Photograph by M. V. S.]

When we consider the reputedly poisonous larvae of moths and b.u.t.terflies, one of the first things to impress us is that we cannot judge by mere appearance. Various species of Sphingid, or hawk-moth larvae, bear at the end of the body a chitinous horn, which is often referred to as a "sting" and regarded as capable of inflicting dangerous wounds. It would seem unnecessary to refer to this absurd belief if it were not that each summer the newspapers contain supposed accounts of injury from the "tomato worm" (fig. 29) and others of this group. The grotesque, spiny larva (fig. 30) of one of our largest moths, _Citheronia regalis_ is much feared though perfectly harmless, and similar instances could be multiplied.

[Ill.u.s.tration: 31. The flannel moth (Lagoa crispata). (_a_) Poisonous larva.]

[Ill.u.s.tration: 31. (_b_) Adult. Enlarged. Photographs by M. V. S.]

But if the larvae are often misjudged on account of their ferocious appearance, the reverse may be true. A group of most innocent looking and attractive caterpillars is that of the flannel-moth larvae, of which _Lagoa crispata_ may be taken as an example. Its larva (fig. 31) has a very short and thick body, which is fleshy and completely covered and hidden by long silken hairs of a tawny or brown color, giving a convex form to the upper side. Interspersed among these long hairs are numerous short spines connected with underlying hypodermal poison glands. These hairs are capable of producing a marked nettling effect when they come in contact with the skin. This species is found in our Atlantic and Southern States. Satisfactory studies of its poisonous hairs and their glands have not yet been made.

[Ill.u.s.tration: 32 The poisonous saddle back caterpillar. Empretia (Sibine) stimulea. Photograph by M. V. S.]

[Ill.u.s.tration: 33_a_. Io moth larvae on willow. Photograph by M. V. S.]

_Sibine stimulea (Empretia stimulea)_, or the saddle-back caterpillar (fig. 32), is another which possesses nettling hairs. This species belongs to the group of Eucleidae, or slug caterpillars. It can be readily recognized by its flattened form, lateral, bristling spines and by the large green patch on the back resembling a saddle-cloth, while the saddle is represented by an oval, purplish-brown spot. The small spines are venomous and affect some persons very painfully. The larva feeds on the leaves of a large variety of forest trees and also on cherry, plum, and even corn leaves. It is to be found throughout the Eastern and Southern United States.

[Ill.u.s.tration: 33_b_. Io moth. Full grown larva. Photograph by M. V. S.]

[Ill.u.s.tration: 34. Io moth. Adult. Photograph by M. V. S.]

_Automeris io_ is the best known of the nettling caterpillars. It is the larva of the Io moth, one of the Saturniidae. The mature caterpillar, (fig. 33), which reaches a length of two and one-half inches, is of a beautiful pale green with sublateral stripes of cream and red color and a few black spines among the green ones. The green radiating spines give the body a mossy appearance. They are tipped with a slender chitinous hair whose tip is readily broken off in the skin and whose poisonous content causes great irritation. Some individuals are very susceptible to the poison, while others are able to handle the larvae freely without any discomfort. The larvae feed on a wide range of food plants. They are most commonly encountered on corn and on willow, because of the opportunities for coming in contact with them.

[Ill.u.s.tration: 35. Larva of brown-tail moth. (Natural size). Photograph by M. V. S.]

The larvae of the brown-tail moth (_Euproctis chrysorrha_) (fig. 35 and 36), where they occur in this country, are, on account of their great numbers, the most serious of all poisonous caterpillars. It is not necessary here, to go into details regarding the introduction of this species from Europe into the New England States. This is all available in the literature from the United States Bureau of Entomology and from that of the various states which are fighting the species. Suffice to say, there is every prospect that the pest will continue to spread throughout the Eastern United States and Canada and that wherever it goes it will prove a direct pest to man as well as to his plants.

Very soon after the introduction of the species there occurred in the region where it had gained a foothold, a mysterious dermat.i.tis of man.

The breaking out which usually occurred on the neck or other exposed part of the body was always accompanied by an intense itching. It was soon found that this dermat.i.tis was caused by certain short, barbed hairs of the brown-tail caterpillars and that not only the caterpillars but their coc.o.o.ns and even the adult female moths might harbor these nettling hairs and thus give rise to the irritation. In many cases the hairs were wafted to clothing on the line and when this was worn it might cause the same trouble. Still worse, it was found that very serious internal injury was often caused by breathing or swallowing the poisonous hairs.

[Ill.u.s.tration: 36. Browntail moths. One male and two females. Photograph by M. V. S.]

The earlier studies seemed to indicate that the irritation was purely mechanical in origin, the result of the minute barbed hairs working into the skin in large numbers. Subsequently, however, Dr. Tyzzer (1907) demonstrated beyond question that the trouble was due to a poison contained in the hairs. In the first place, it is only the peculiar short barbed hairs which will produce the dermat.i.tis when rubbed on the skin, although most of the other hairs are sharply barbed. Moreover, it was found that in various ways the nettling properties could be destroyed without modifying the structure of the hairs. This was accomplished by baking for one hour at 110 C, by warming to 60 C in distilled water, or by soaking in one per cent. or in one-tenth per cent. of pota.s.sium hydrate or sodium hydrate. The most significant part of his work was the demonstration of the fact that if the nettling hairs are mingled with blood, they immediately produce a change in the red corpuscles. These at once become coa.r.s.ely crenated, and the roleaux are broken up in the vicinity of the hair (fig. 37_b_). The corpuscles decrease in size, the coa.r.s.e crenations are transformed into slender spines which rapidly disappear, leaving the corpuscles in the form of spheres, the light refraction of which contrasts them sharply with the normal corpuscles. The reaction always begins at the basal sharp point of the hair. It could not be produced by purely mechanical means, such as the mingling of minute particles of gla.s.s wool, the barbed hairs of a tussock moth, or the other coa.r.s.er hairs of the brown-tail, with the blood.

[Ill.u.s.tration: 37. (_a_) Ordinary hairs and three poison hairs of subdorsal and lateral tubercles of the larva of the browntail moth.

Drawing by Miss Kephart.]

The question of the source of the poison has been studied in our laboratory by Miss Cornelia Kephart. She first confirmed Dr. Tyzzer's general results and then studied carefully fixed specimens of the larvae to determine the distribution of the hairs and their relation to the underlying tissues.

[Ill.u.s.tration: 37. (_b_) Effect of the poison on the blood corpuscles of man. After Tyzzer.]

The poison hairs (fig. 37), are found on the subdorsal and lateral tubercles (fig. 38), in bunches of from three to twelve on the minute papillae with which the tubercles are thickly covered. The underlying hypodermis is very greatly thickened, the cells being three or four times the length of the ordinary hypodermal cells and being closely crowded together. Instead of a pore ca.n.a.l through the cuticula for each individual hair, there is a single pore for each papillae on a tubercle, all the hairs of the papilla being connected with the underlying cells through the same pore ca.n.a.l, (figs. 39 and 40).

[Ill.u.s.tration: 38. Cross section of the larva of the browntail moth showing the tubercles bearing the poison hairs. Drawing by Miss Kephart.]

The hypodermis of this region is of two distinct types of cells. First, there is a group of slender fusiform cells, one for each poison hair on the papilla, which are the trichogen, or hair-formative cells. They are crowded to one side and towards the bas.e.m.e.nt membrane by a series of much larger, and more prominent cells (fig. 40), of which there is a single one for each papilla. These larger cells have a granular protoplasm with large nuclei and are obviously actively secreting. They are so characteristic in appearance as to leave no question but that they are the true poison glands.

[Ill.u.s.tration: 39. Epithelium underlying poison hairs of the larva of the browntail moth. Drawing by Miss Kephart.]

Poisonous larvae of many other species have been reported from Europe and especially from the tropics but the above-mentioned species are the more important of those occurring in the United States and will serve as types. It should be noted in this connection that through some curious misunderstanding Gldi (1913) has featured the larva of _Orgyia leucostigma_, the white-marked tussock moth, as the most important of the poisonous caterpillars of this country. Though there are occasional reports of irritation from its hairs such cases are rare and there is no evidence that there is any poison present. Indeed, subcutaneous implantation of the hairs leads to no poisoning, but merely to temporary irritation.

[Ill.u.s.tration: 40. Same as figure 39, on larger scale.]

Occasionally, the hairs of certain species of caterpillars find lodgement in the conjunctiva, cornea, or iris of the eye of man and give rise to the condition known as _opthalmia nodosa_. The essential feature of this trouble is a nodular conjunctivitis which simulates tuberculosis of the conjunctiva and hence has been called _pseudo-tubercular_. It may be distinguished microscopically by the presence of the hairs.

[Ill.u.s.tration: 41. (_a_) Nodular conjunctivitis in the eye of a child.

De Schweinitz and Shumway.]

Numerous cases of opthalmia nodosa are on record. Of those from this country, one of the most interesting is reported by de Schweinitz and Shumway (1904). It is that of a child of fifteen years whose eye had become inflamed owing to the presence of some foreign body. Downward and inward on the bulbar conjunctiva were a number of flattened, grayish-yellow nodules, between which was a marked congestion of the conjunctival and episcleral vessels (fig. 41_a_). Twenty-seven nodules could be differentiated, those directly in the center of the collection being somewhat confluent and a.s.suming a crescentic and circular appearance. The nodules were excised and, on sectioning, were found to be composed of a layer of spindle cells and round cells, outside of which the tissue was condensed into a capsule. The interior consisted of epithelioid cells, between which was a considerable intercellular substance. Directly in the center of a certain number of nodules was found the section of a hair (fig. 41_b_). The evidence indicated that the injury had resulted from playing with caterpillars of one of the Arctiid moths, _Spilosoma virginica_. Other reported cases have been caused by the hairs of larvae of _Lasiocampa rubi_, _L. pini_, _Porthetria dispar_, _Psilura monacha_ and _Cnethocampa processionea_.

[Ill.u.s.tration: 41_b_. Section through one of the nodules showing the caterpillar hair. De Schweinitz and Shumway.]

RELIEF FROM POISONING BY NETTLING LARVae--The irritation from nettling larvae is often severe and, especially in regions where the brown-tail abounds, inquiries as to treatment arise. In general, it may be said that cooling lotions afford relief, and that scratching, with the possibilities of secondary infection, should be avoided, in so far as possible.

Among the remedies usually at hand, weak solutions of ammonia, or a paste of ordinary baking soda are helpful. Castellani and Chalmers recommend cleaning away the hairs by bathing the region with an alkaline lotion, such as two per cent solution of bicarbonate of soda, and then applying an ointment of ichthyol (10%).

In the brown-tail district, there are many proprietary remedies of which the best ones are essentially the following, as recommended by Kirkland (1907):

Carbolic acid drachm.

Zinc oxide oz.

Lime water 8 oz.

Shake thoroughly and rub well into the affected parts.

In some cases, and especially where there is danger of secondary infection, the use of a weak solution of creoline (one teaspoonful to a quart of water), is to be advised.