ROSS: HOW TO COLLECT AND PRESERVE INSECTS 



31 



Thysanura Wingless, flat insects that run rapidly. They 



Silverfish have long antennae and three long tails. Ter- 



restrial ; commonly found in dwellings. Fig. 

 18 shows one of the common silverfish, Thermobia domestica 

 Packard ; its habit of eating book bindings and other starchy 

 materials is well known to most apartment dwellers. 



Fig. 18. — Thysanura. Thermobia domestica, a common silverfish. Actual 

 length about 0.3 inch. 



Some out-of-door forms inhabit wooded dells, where they hide 

 under logs and stones and, when disturbed, run with remark- 

 able speed. Others live in the soil itself and are rarely collected. 



Collembola Small wingless insects that jump and crawl 



Springtails when disturbed. They have short antennae 



and usually a springing foot on the underside 



near the posterior end of the body. They live in moist places and 



are abundant under leaf mold and similar material. Illustrated 



in fig. 19 is Achorutes armatus (Nicolet), which 



often becomes a major pest in mushroom cellars 



and greenhouses. 



About a hundred different species of Collembola 



occur in Illinois ; they include some of our smallest 



insects. A few never grow longer than 0.007 inch ; 



the largest approach half an inch in length. These 



hardy animals are active all year and surprisingly 



resistant to cold. Certain species occur on snow in 



winter. In Illinois a small 



bluish-gray species, Podura 



aquatica (Linnaeus), is 



found on the surface of still 



water at the margins of 



ponds and small streams. 



Achorutes armatus, a 

 small springtail found 

 in greenhouses and 

 mushroom cellars. Ac- 

 tual length less than 0.1 

 inch. 



