Amongst _Orthoptera_ we find many noxious insects, notably the locusts, which travel in vast cloud-like armies, clearing the whole country before them of all vegetable life. The most destructive locust is the migratory locust (_Locusta migratoria_), which causes wholesale destruction in the East. Large pits are dug across the line of advance of these great insect armies to stop them when in the larval or wingless stage, and even huge bonfires are lighted to check their flight when adult. So dense are these "locust clouds" that they sometimes quite darken the air. The commonest and most widely distributed migratory locust is _Pachytylus cinerascens_. The mole cricket (_Gryllotalpa vulgaris_) and various cockroaches (_Blattidae_) are also amongst the pests found in this order. Of _Neuroptera_ there are but few injurious species, and many, such as the lace wing flies (_Hemerobiidae_), are beneficial. _The Treatment of Insect Pests._--One of the most important ways of keeping insect pests in check is by "spraying" or "washing." This method has made great advances in recent years. All the pioneer work has been done in America; in fact, until the South-Eastern Agricultural College undertook the elucidation of this subject, little was known of it in England except by a few growers. The results and history of this essential method of treatment are embodied in Professor Lodemann's work on the _Spraying of Plants_, 1896. In this treatment we have to bear in mind what the entomologist teaches us, that is, the nature, habits and structure of the pest.