How insects behave 



regardless of their own efforts. This has been particularly observed in 

 locusts. 



Some insects, notably bees, ants and beetles, have been shown to be 

 able to steer a course by the sun, the so-called ' hght-compass reaction'. 

 The Robinson Light Trap is based upon a similar reaction in moths and 

 other night-flying insects. The insect tries to keep the point of hght 

 on the same facets of the eye all the time. If the source of light is far 

 away, e.g. the sun or the moon, then the insect continues in a straight 

 line, keeping a constant angle to the beam of Hght. When the hght 

 comes from a lamp not far away, the only way to keep a constant angle 

 to the beam is to turn steadily towards the lamp in a spiral path, v/hich 

 eventually brings the insect into the trap. 



Difficulties arise when this theory is applied to migrating insects, 

 which continue in the same direction for days, or even weeks. Williams 

 points out that they would have to make a continuous correction for the 

 apparent movement of the sun through the day, and moreover they are 

 able to carry on just the same on a dull day, or a moonless night, or 

 after they have been interrupted by bad weather. 



Certain insects, notably migratory aphids, seem to need a period of 

 active flight before they can settle down and reproduce, but in general 

 *we know neither the external cause nor the internal mechanism' of the 



Fig. 60. A solitary wasp, Order Hymenoptera-Aculeata 



91 



