“No; nor do any damage if it did. The luna is as harmless as it is lovely. In this case the moths weren’t active agents. They were important only as clues—and bait. Their enormous size showed Professor Moseley’s line of work; the selective breeding of certain forms of life to two or three times the normal proportions. Very well; I had to ascertain some creature which, if magnified several times, would be deadly, and which would still be capable of entering a large keyhole. Having determined that—” “You found what it was?” cried Dorr. “One moment. Having determined that, I had still to get in touch with Professor Moseley’s mysterious New York correspondent. I figured that he must be interested in Professor Moseley’s particular branch of research or he never could have devised his murderous scheme. So I constructed the luna moth advertisement to draw him, and when I got a reply from Mr. Ross, who is a fellow-tenant of Mr. Dorr’s, the chain was complete. Now, you see where the luna moths were useful. If I had advertised, instead of them, the _lathrodectus_, he might have suspected and refrained from answering.” “What’s the _lathrodectus?_” demanded both the hearers at once. For answer Average Jones took a letter from his pocket and read: BUREAU OF ENTOMOLOGY, U. S. DEPARTMENT OF AGRICULTURE, WASHINGTON, D. C., April 7 MR. A. V. R. JONES, Astor Court Temple, New York City. DEAR Sir, Replying to your letter of inquiry, the only insect answering your specifications is a small spider _Lathrodectus mactans_, sometimes popularly called the Red Dot, from a bright red mark upon the back. Rare cases are known where death has been caused by the bite of this insect. Fortunately its fangs are so weak that they can penetrate only very tender skin, otherwise death from its bite would be more common, as the venom, drop for drop, is perhaps the most virulent known to science. This Bureau knows nothing of any experiments in breeding the _Lathrodectus_ for size. Your surmise that specimens of two or three times the normal size would be dangerous to life is undoubtedly correct, and selected breeding to that end should be conducted only under adequate scientific safeguards. A _Lathrodectus mactans_ with fangs large enough to penetrate the skin of the hand, and a double or triple supply of venom, would be, perhaps, more deadly than a cobra. The symptoms of poisoning by this species are spasms, similar to those of trismus, and agonizing general pains. There are no local symptoms, except, in some cases, a circle of small pustules about the bitten spot. Commercially, the _Lathrodectus_ has value, in that the poison is used in certain affections of the heart. For details, I would refer you to the Denny Laboratories of St. Louis, Mo., which are purchasers of the venom. The species is very susceptible to cold, and would hardly survive a severe frost. It frequents woodpiles and outhouses. Yours truly, L. O. HOWARD, Chief of Bureau.