LIFE-HISTORY. 157 



are : The longicorn beetle, Gracilia pygmaea, Fabr., which came 

 to Germany in the hoops of casks made of willows or oak. 

 Species of Li/ctus were imported in Australian wood. The 

 destructive Colorado beetle (Doryphora deccmlincata) came 

 from America with a cargo of potatoes. The phylloxera 

 {P. vastatrix, Planch) on American vines. 



3. Mobility. 



The mode and degree of rapidity with which insects move 

 may be usually inferred from the structure of their organs of 

 locomotion. Some insects have legs for running, as ground- 

 beetles ; for jumping, as fleas ; for digging, as crickets ; for 

 swimming, as water-beetles. 



The imagos run or fly ; their course being rapid {Carahns), 

 or slow {Ceramhyx) ; their flight is either fast (Bomhus), slow 

 {Mdolonth<i), irresolute (Papilio), or hovering (Syiplius) ; ex- 

 tended {Sphyux pinastri, L.), or short {Gryllns). The flight 

 of the ? * is heavier than that of the 3 , especially when she 

 is laden with eggs. 



The mobility of the larvae depends largely on the number of 

 their legs (6, 8, 10, 16, 18, 22), all but six of which are soft 

 and fleshy prolegs. Many lepidopterous caterpillars assist 

 their movements by spinning threads, such as those of many 

 Bombyces, Geometers and Tortrices {e.g. Tortrix viridana, L.) 



4. Food. 



Metabolic insects feed only as larvaB and imagos, and chiefly 

 in the former state. Thus, the food of butterflies and moths 

 is limited to the nectar of flowers. Some beetles, however, 

 are destructive as imagos only {Ilylohius ahietis, L., etc.). 

 Ametabolic insects also feed in the pupal stage. The appetite 

 of larvae in both groups is enormous, and there are larvae 

 which eat daily more than their own weight of food. 



Insects may be termed caniicorous ox phytophagous, according 

 as their diet is animal or vegetable. Most insects useful to 

 the forester belong to the former category, whilst plant-feeders 

 are all more or less injurious. 



* The symbol ? denotes the female, ^ the male, and >? the worker, or 

 imperfect female. 



