ENTOMOLOGY IN OUTLINE— IIYMENOPTKKA. 115 



structure and habits than occurs in tliis family. This co-rehition 

 descends to the relation between the parasites and their hosts, so that 

 it is possible for an experienced person on seeing a new species of 

 Chalcid tly to tell precisely what kind of an insect it will be found to 

 be parasitic upon. For example, the species of the genus Cnjridosoma 

 are always parasitic within naked caterpillars. Those of tlie genus 

 Bothriothonix are always parasitic in small dipterous larva". The 

 economic importance of the group is great. They are the most effective 

 parasites of many of our most injurious insects. For example, in 

 a certain year in the cotton fields of northern Florida ninety-five 

 per cent of the eggs from which would have hatched the voracious 

 cotton-caterpillar were killed by the minute Chalcid parasite, Tricho- 

 gramma pietiosa.^^ 



In our own State, the different species of this family form one of the 

 most efficient checks on scale pests, usually burrowing into the scale 

 and eating it out. How exceedingly minute some of them are is indi- 

 cated by the fact that the red, yellow, and San Jose scales are all para- 

 sitized by members of this family, and, within the bodies of these 

 insects, none of which are larger than the head of a pin, these little 

 flies have ample room to live, grow, pass through all their changes, and 

 emerge as perfect insects. We have often found from three to five 

 parasites belonging to this group snugly ensconced within the body of a 

 soft brown scale, and there was ample room for all without crowding. 



Some of the Chalcids attack larger insects, and the cabbage- butterfly 

 is largely kept down by the efforts of one of them, Pieromalus puparum, 

 which lays its eggs on the caterpillar and reduces it to a state of 

 "innocuous desuetude." One branch of the family closely approaches 

 the gall-flies in structure and habits. 



The family Proetotrupidse contains the smallest members of the 

 Hymenoptera. They are all parasitic, many of them being parasitic on 

 the eggs of other insects. How small they are may be understood by 

 the statement that, in some cases, as many as half-a-dozen of them will 

 live and pass through all their changes within one minute egg of an 

 insect, moth, butterfly, or bug. Some live in the larvte of other insects, 

 some exist wholly in the nervous system, others in the digestive tract. 

 The largest of them is not over one twenty-fifth of an inch in length, 

 while the smallest {Alaptus excisus) measures between six and seven 

 one-thousandths of an inch. 



Suborder ACULEATA. 



We now come to the second branch or suborder of tlie Hymenoptera, 

 which includes the species armed with stings. Most of our readers 

 have made acquaintance with them, as the group includes the wasps, 



