312 



THE AGEICULTURAL XEWS. 



Septembee 26, 1914. 



INSECT NOTES. 



INSECTS AND PAIN. 



The aeconipaiiying article fiititled Insect.s and 

 Pain, by Mr. H. B. Weiss, is taken from the Canadian 

 Entomologist for August 1914: — 



This article is of interest as a diseussion of the 

 extent to which insects expei-ience pain as understood 

 by the hmiian animal, but the author is not able to 



• arrive at a definite ccnclusion in the matter. It wotdd 

 seeni that while insects have well developed nervous 

 systems, the human intelligence has no means of 



. accurately gauging the kind of sensation which is felt 

 by the insect, under conditions which in us would pro- 



•duce pain in v:irious degrees (^f intensity, shading off to 

 slight irritation, inconvenience or annoyance: — 



In VHiious liiioks on entomology one often conies acro.ss 

 the statement that insects do not suiter acute sensations of 

 pain as do the higher animals. I )itferent facts are cited to 

 prove this, the most familiar l>eing the case of a buttertly 

 that was pinned alive, escaped and retiu'iied to its feeding 

 among flowers with ajjparently no inconvenience. Kirl)V 

 and S]3enee c]note the action of a bee eating honey though 



• deprived of its abdomen. Dr. John B. Smith found that if 

 he cut off the abdomen of a fly it would live for twenty-four 

 liours after with jjractically no digestive system, very little 

 nervous system and most of its heart gone, and when the 

 head was removed it lived for the same length of time. The 

 interesting feature was that no apparent sym|)tom of pain 

 was developed. 



It is alsfi said that if a dragonfly lie cairtured, held 

 loosely by the wing and the tip nf its abdomen jaesented to 

 it-s raoutli, it will proceed to eat it at once as far as it 

 can reach. 



Itcfcning to the human system, many experiences com- 

 in<inly called painful are only unpleasant or disagreeable. 

 This 1-1 infusion is due to the fact that painful things are 

 -.ilways unpleasant. Painfulness however is ipiite distinct 

 fmrn unplea.santness. The same stimuli wliieh result in 

 Sensations of pressure, warmth and cold may alsci bring abnut 

 painfulness if they are long continued ur repeated ciften 

 enough. 



There are varinus tlienries accounting fur pain sensations, 

 the oldest one teaching that there was no specitic pain organs 

 but that sensations of ]jain were brought about Ijy continued 



•or excessive reactions of other end-organs, especially those of 

 pressure. This theory was disproveil by the discovery that 



■certain anaesthetics destroyed pain sensations independently 



■of pressure sensations. For instance, if one's tooth is treated 

 witli cocaine, no pain is felt upon its removal but one is con- 

 •scioiis <if the pressure of the dentist's instrument. 



, Anotlier theory is that pain is produced only by the 



■excitation of distinct end-organs of pain. This theory is 

 ba.sed on the discovery of pain spots on the skin. However, 

 the spots which are sensitive to pain and not to pressure have 

 been found to occur oidy on the elbow joints and membranous 



■coverings of the eye. This lack of sjjots is explained Viy 

 •ussumiiig that nifire stimulation is reipiired to excite pain 



■end-organs than pressure end-oigans. 



\ third theory is that pain end-organs are not distinct 

 •from pressure end-organs but are exposed pressure organs 

 situated under unusually thin parts of the epidermis and that 

 .pain is not due to any activity of these end-organs but to 

 ■'a. transformation in the grey matter of the spinal cord of 



nerve excitations conveyed from tliese exposed pressure 

 end-organs.' 



Returning to insects we find that they have well devel- 

 <iped nervous systems anH that their organs are well supplied 

 with nerve endings. Moreover many insects give signs of 

 discomfort when handled or nuitilated. There is no doubt 

 but that they are highly susceptible to pressure stimuli. In 

 fact end organs of touch such as hairs and bristles are dis- 

 tributed over the entire integument. 



Pain sensations however are hard to distinguish in 

 insects from those of touch. One argues that the mutilated 

 insects heretofore referred to, experienced no pain simply 

 because they exhibited no signs of suft'ering. What then 

 constitutes a symptom of pain in in.sects? Who is qualified to 

 judge? !Mauy i)ain racked persons go about their duties with- 

 out exhibiting any signs of pain other than changes in facial 

 expression. Of course, extreme mutilation of the human body 

 results in almost inunediate death, while in the ca.se of insects 

 death is not inunediate. All pain, however, is an exhausting 

 experience and injiuious to the organism. With insects flnal 

 exhaustion is simply deferred. 



In the case of the dragonfly eating its own body, it is 

 hard to find a human parallel unless we cite mentally un- 

 balanced jjcrsons w ho inflict serious injuries tipou their person. 

 One might argue that they woidd not do this if it were pain- 

 ful and yet we are jjositive such actions are painful. 



The character of the insect nervous sy.stem is ludike our 

 own. and the surface of their bodies is usually rigid and hard 

 and probably mit sensitive to pressure ami pain in the same 

 way as our own Iiodies, so that we have no reliable guides as 

 to their sensations of pain. Man judges most things liy him- 

 self and when this guide fails he is at a loss to explain certain 

 haiipenings in a satisfactory way. It seems therefore, that the 

 e\idence for assuming that in.sects do not suffer acute 

 sensations of jiain is not b\- any means complete. We simply 

 do not know and have.no rclialile means at present of tiniling 

 oiu. 



According to the Jievieif of Apjilied Entomolo'iy for 

 June 1914, the fioverinnent Veterinary .Surgeon in t'eyhm 

 reports that serious trouble has l>een cau.sed in Ceylon by 

 Stoiao.iys valcitranf, which was found to l>e swarming in one 

 of the towns and a cau.se of .serious irritation to cattle and 

 horses. The eggs, which are usually laid in ma.sses in straw, 

 hatch in from one to three days. The larva completes its 

 growth in about eknien days, and six days later the adult 

 emerges from the puparium. Green in Ceylon has bred 

 .S. calcitrans from decayed pumpkins and S. plurinotata from 

 decayed shoots of the giant liamboo. It will be rcniemliered 

 that S. calcitrans occurs in the West Indies and South 

 America and is supjjo.sed to be the transmitter, or one of the 

 transmitters of Mai de Caderas. 



An inijxatant point in connexion with water culture 

 experiments is referred to in the Monthli/ Bulletin of Afjri- 

 cultural Intellitience and Plant Diseases for .June 1914. 

 Culture experiments with Afjiernillus niijer in Kaulin's solu- 

 tion with and without zinc showed ditt'erent results according 

 to the nature of the vessel employeil. In a .solution of hjdro- 

 chloric acid ei|uivalent in acidity to that of Kaulin's solution, 

 the writer found O'Oo milligrannne of zinc per 1"2.tc.c. h\ 

 these experiments lioheniian glass, Jena glass and ijuartz 

 gla.ss were used, and there was a liig variation, as shown liy 

 the flgures in the .solution with zinc ami the .solution without, 

 zinc. 



