2i8 INJURIOUS AND USEFUL INSECTS 



The larvae are hairy and dark-coloured, so that they resemble 

 small caterpillars ; they devour fur, hides, carpets, horse-hair, 

 food-stores of many kinds, and dried animal substances. 

 Some {Dermestes lardarius, D. vulpinus, Attagenus pellio, 

 Anthrenus ?nuseorum) are common plagues in collections of 

 stuffed animals. 



Sub-order IV. — Serricomia (serricorn beetles) 



Tarsus five-jointed in all the legs (with some exceptions). 

 Antennae often serrate or pectinate — i.e. with each joint pro- 

 jecting more or less inwards at its further end. An unsatis- 

 factory division. 



Family Ptinidse. Small, rounded beetles, with slender 

 antennae and s-jointed tarsus. 



The larvae of some species of Anobium drill holes in furni- 

 ture; another is the "weevil" of sailors, which devours, ship- 

 biscuits. Ptinus fur is often very destructive in museums. 

 Some make a ticking noise as a signal to their mates, and 

 are on this account (like Psocidse) called death-watches. 



Family Elateridse (click-beetles). Antennse variable, often 

 serrate. Prothorax movable on mesothorax. Can leap when 

 placed on their backs (see Lesson 7). 



Family Lampsrridae (glow - worms). Antennae variable. 

 Many emit light from the hinder part of the abdomen. In 

 some the female beetle has the wings short or absent. 



The females, which alone emit a bright light, are wingless, 

 and resemble larvae. The males are winged, and are gifted 

 with much larger eyes than the females. It is probable, 

 therefore, that one chief purpose of the light is to allure the 

 males. The males, however, and even the eggs, are slightly 

 luminous. The glow-worm is concealed by day, but makes 

 herself more evident at night by climbing upon stalks or low 

 shrubs. The light is intermittent, being given out in the form 

 of flashes, which succeed one another with great rapidity. 

 When alarmed or disturbed, the glow-worm can extinguish its 

 light. Close examination shows that the glow proceeds from 

 a fatty substance which shines through the transparent parts 

 of the skin on the hinder segments of the abdomen. The 

 luminous substance contains no phosphorus, and it is believed 

 that the light is caused by the slow oxidation of oily matter. 



