8 



BULLETIN 986, IT. S. DEPARTMENT OF AGRICULTURE. 



due to chiggers, were found to be due to Hyletastes missouriensis 

 Ewing, a gamasid mite, the habits of which are not well known. 



Injury from fleas is very similar to the first-stage injury of chig- 

 gers, and since fleas soon leave their hosts and chiggers are so small 

 that they frequently are overlooked, flea injury is mistaken for 

 chigger injury. A careful examination with a hand lens will enable 

 one to see the attached chiggers and prevent confusion of flea injury 

 with an attack by chiggers. 



DO CHIGGERS PENETRATE THE SKIN? 



Both among entomologists and the public generally there is a 

 belief that chiggers burrow into the skin. C. V. Eiley (10) states 



in regard to his irritans that " This mite 

 is able to bury itself completely in the 

 flesh." In speaking of the same chigger, 

 ee^ / f^^= ^ Osborn (8, p. 252) sys : " It is brushed 



from the leaves of various plants onto the 

 hands or clothing of people and to the 

 bodies of other animals, and the mite then 

 proceeds to burrow into the skin." 



To find out whether chiggers penetrate 

 the skin or not, and also to observe their 

 injur} 7 , resort was made to experimenta- 

 tion. On July 15, 1919, the writer exposed 

 the left calf and ankle to chigger attack, 

 and after the mites had settled numbered 

 10 individuals by writing on the flesh near 

 the mite with ink. Daily observations were 

 made on these chiggers, using low and high 

 power lenses, for the next eight days. It was observed on the first 

 day that the mites attached only by their mouthparts and in no way 

 burrowed into the skin. Observations on the second day showed no 

 change ; in fact, after once attaching to the skin by their mouthparts 

 the larvae became quiescent and did not change their position until 

 they dropped off. 



By means of a razor blade several individuals were removed by 

 slicing off a small area of the epidermis around them. When this 

 " slice " of epidermis was examined under a high-power micro- 

 scope objective it showed the attachment as represented in figure 3. 

 The hooked and ventrall} 7 barbed chelicerse were thrust into the 

 epidermis only, and the palpal claws were found forced downward 

 and backward into the epidermis. After both the cheliceraB and 

 the palpi have been inserted in this fashion they hold the larva 

 locked, as it were, to the skin. This was made evident by watch - 



Fig. 3. — View showing the 

 method of attachment of a 

 chigger (northeastern spe- 

 cies) . Drawing of a part 

 of a " slice " of skin, made 

 from the underside while 

 the larva was attached. 



