FLY-FLOWERS 



this locality, and that the twinflower is an Empis flower. The 

 males of the dance-flies live wholly on flowers, but the females 

 are partly predaceous. 



The milkweeds are pinch-trap flowers, which in their remark- 

 able pollinating mechanism rival the orchids. The pollen 

 coheres in waxy masses called poUinia, which by means of an 

 ingenious clip-mechanism are clamped to the legs, tongues, and 

 antennae of flies and many other insects. When the insect flies 

 to another flower the pollinia come in contact with the stigma, 

 to which they adhere so firmly that it can only obtain its 

 liberty by snapping the connecting bands. Only a part of the 

 species of Asclepias are pollinated by flies, others are pollinated 

 by bees and butterflies. It is not uncommon in examining 

 specimens of bees to find one or more of these clips, which are 

 a useless burden and interfere with their work, on their legs and 

 antennae. Gibson states that an English bee-keeper lost thou- 

 sands of his bees from the effects of strings of these clips, which 

 it was at first thought were a fungous growth. (Fig. 86.) 



If an insect caught in one of these pinch-traps is not strong 

 enough to pull away the pollinia or break the bands, it is held 

 a prisoner and dies a lingering death, although probably a 

 nearly painless one. In New Zealand the flowers of Araugia 

 alhens, a plant introduced from the Cape of Good Hope, which 

 are normally pollinated by bumblebees, catch in a single 

 night hundreds of moths. It was once seriously proposed by 

 an economic entomologist to employ this plant in the extermi- 

 nation of the codling-moth, so injurious to apples; but unfortu- 

 nately the co-operation of the codling-moth could not be ob- 

 tained, for it persistently refused to visit the flowers of Araugia 

 — another illustration that the well-laid schemes of mice and 

 men — 



" Gang aft a-gley." 

 177 



