A species which very commonly attacks man is _Conorhinus sanguisugus_, the so-called "big bed-bug" of the south and southern United States. It is frequently found in houses and is known to inflict an exceedingly painful bite. As in the case of a number of other predaceous Hemiptera, the salivary glands of these forms are highly developed. The effect of the bite on their prey and, as Marlatt has pointed out, the constant and uniform character of the symptoms in nearly all cases of bites in man, clearly indicate that their saliva contains a specific substance. No satisfactory studies of the secretions have been made. On the other hand, Dr. Howard is doubtless right in maintaining that the very serious results which sometimes follow the bite are due to the introduction of extraneous poison germs. This is borne out by the symptoms of most of the cases cited in literature and also by the fact that treatment with corrosive sublimate, locally applied to the wound, has yielded favorable results. OTHER HEMIPTERA REPORTED AS POISONOUS TO MAN--A large number of other Hemiptera have been reported as attacking man. Of these, there are several species of Lygæidæ, Coreidæ, and Capsidæ. Of the latter, _Lygus pratensis_, the tarnished plant-bug, is reported by Professor Crosby as sucking blood. _Orthotylus flavosparsus_ is another Capsid which has been implicated. _Empoasca mali_ and _Platymetopius acutus_ of the Jassidæ have also been reported as having similar habits. Whenever the periodical cicada or "seventeen-year locust" becomes abundant, the newspapers contain accounts of serious results from its bites. The senior author has made scores of attempts to induce this species to bite and only once successfully. At that time the bite was in no wise more severe than a pin-prick. A student in our department reports a similar experience. There is no case on record which bears evidence of being worthy of any credence, whatsoever. Under the heading of poisonous Hemiptera we might consider the bed-bugs and the lice. These will be discussed later, as parasites and as carriers of disease, and therefore need only be mentioned here. DIPTERA Several species of blood-sucking Diptera undoubtedly secrete a saliva possessing poisonous properties. Chief among these are the Culicidæ, or mosquitoes, and the Simuliidæ, or black-flies. As we shall consider these forms in detail under the heading of parasitic species and insects transmitting disease, we shall discuss here only the poison of the mosquitoes.