264 THE FRIENDS AND ASSOCIATES 



The cause of this friendship and association is not 

 far to seek, for a slight observation of the action of 

 the ants will show that they have a reason for their 

 devotion to the caterpillars. They tend these as 

 they tend plant lice, because each of them has the 

 power of exuding, from special glands near the ex- 

 tremity of the body, a droplet of fluid having a 

 saccharine character, and thus attractive to ants, 

 whose fondness for sweet things is well known to 

 every housekeeper. In the butterfly caterpillars, 

 as may be found in any description of these 

 forms, this gland is situated in the middle of the 

 body on the seventh abdominal segment, and now 

 and then, at the solicitation of the ants, by the 

 stroking of their antennae, is evaginated and a 

 droplet of fluid exposed, which the ants greedily 

 lap up. 



Now, although the only caterpillars attended ])y 

 ants belong to the blue butterflies, the gland which 

 secretes the sugary fluid is not confined to the 

 caterpillars of these butterflies, but is also found 

 in many of their immediate allies, namely, in most 

 of the Hair-streaks or Theclini, and in one at least 

 of the Coppers, Tomares ballus of Europe. Two 

 explanations readily offer themselves : one, that in 

 caterpillars so little known as are these, it may 



